ECOLOGY OF THE GULF COAST AND ISLANDS OF SONORA ...

Tide dissertation has been 

microfilmed exactly as received 66-15,247 

FELGER, Richard Stephen, 1934- 

ECOLOGY OF THE GULF COAST AND ISLANDS OF 

SONORA, MEXICO. 

University of Arizona, Ph.D., 1966 

Zoology 

University Microfilms, Inc., Ann Arbor, Michigan

© COPYRIGHTED 

BY 

RICHABD STEPHEN FELGER 

1967 

ill

ECOLOGY OP THE GULP COAST AND 

ISLANDS OP SONOBA, MEXICO 

by 

Richard Stephen Pelger 

A Dissertation Submitted to the Faoulty of the 

DEPARTMENT OP ZOOLOGY 

In Partial Pulfillaient of the Requirements 

Por the Degree of 

DOCTOR OP PHILOSOPHY 

In the Graduate College 

THE UNIVERSITY OF ARIZONA 

19 6 6

THE UNIVERSITY OF ARIZONA 

GRADUATE COLLEGE 

1 hereby recommend that this dissertation prepared under my 

direction by RICHARD STEPHEN FELGER 

entitled ECOLOGY OF THE GULF COAST AND ISLANDS OP 

SONORA. MEXICO 

be accepted as fulfilling the dissertation requirement of the 

degree of DOCTOR OF PHILOSOPHY 

Dissertation Director Date 

After inspection of the dissertation, the following members 

of the Final Examination Committee concur in its approval and 

recommend its acceptance:* 

ft 

%/UC 

f mULy /9(e(, 

*This approval and acceptance is contingent on the candidate's 

adequate performance and defense of this dissertation at the 

final oral examination. The inclusion of this sheet bound into 

the library copy of the dissertation is evidence of satisfactory 

performance at the final examination.

STATEMENT BY AUTHOH 

This dissertation has been submitted in partial 

fulfillment of requirements for an advanced degree at The 

University of Arizona and is deposited in the University 

Library to be made available to borrowers under rules of 

the Library. 

Brief quotations from this dissertation are allowable 

without special permission, provided that accurate 

acknowledgment of source is made. Bequests for permission 

for extended quotation from or reproduction of this manuscript 

in whole or in part may be granted by the copyright 

holder. 

SIGHED t 

?

ACKNOWLEDGMENTS 

I am grateful to Dr. Charles H. Loire for his 

generous guidance, assistance, and orltlolsm throughout 

this work and for introducing me to the islands in the 

Gulf of California. 

I thank Mr* Alexander Russell for generously pro 

viding transportation on numerous occasions and for his 

companionship and assistance in the field. Mr. Robin 

Thomas assisted in the quadrat studies* often under 

adverse conditions. 

Many friends have gone far out of their way to 

oolleot specimens and have aooompanled and assisted me in 

the field. In this regard I sincerely thank Mona Dayton* 

Oda Klelne, Riohard Xrizman, Jean Russell, Oscar Soule, 

Alice and Nanoy Thomas t and Paula Vreeland. 

I thank Major and Dona Vela of Guaymas, Senora 

Gavina Garcia of Bah£a Kino, and Mr. and Mrs. Ed. Moser 

of Desemboque for their generous hospitality. They have 

very graoiously allowed preparation and storage of speci 

mens and equipment in their homes. 

1 am indebted to Miss Mary Franoes Hamilton for 

spending many hourB curating speoimens upon which most of 

this work is based. 

iv

Dr. Howard K. Gloyd, Dr. Albert Mead, and Mr. 

Robert Bezy read the aanusoript and their suggestions are 

greatly appreciated. 

V

TABLE OF CONTENTS 

PAGE 

INTRODUCTION 1 

MATERIALS AND METHODS 10 

DESCRIPTION AND ANALYSIS OF COMMUNITIES Ik 

GUAYMAS REGION . 16 

Bahfa Sail Carlos 17 

Bah£a San Pedro. 63 

13LA SAN PEDRO NOLASCO 91 

LIANURAS DE SAN JUAN BAUTISTA 113 

Punta Baja ••••••••••••••••• 116 

I SLA ALCATRAZ 13^ 

I SLA SAN PEDRO MARTIR 150 

ISLA TIBUBON 158 

Southwest Coast (Ensenada Blanoa)• • • • • « 169 

East Coast (Palo Flerro and Santa Rosa). • • 183 

South-Central Region (Sauzal)* ....... 211 

Interior or Upper Central Valley •••••• 230 

North Coast (Teeomate) 251 

ISLA SAN ESTEBAN 268 

ISLA DATIL 292 

ISLA CH0LLUD0 302 

vl

TABLE OP CONTENTS—Continued 

vil 

PAGE 

INFERNILLO REGION. . 310 

Santa Rosa ......... 316 

Sargento 340 

ISLA PATOS 351 

DISCUSSION 361 

The Vegetation Continuum and Nosaio. . • • . 361 

Speoies Distribution 364 

Life-form 380 

Life-fora Speotra on Isla Tiburon and in the 

Infemillo Region. . . 400 

SUMMARY AND CONCLUSIONS **11 

APPENDIX A • • * ^14 

-APPENDIX 439 

APPENDIX 444 

LITERATURE CITED 448

LIST OF TABLES 

TABLE PAGE 

1. PLOT 1. STRAND AT NORTHWEST SIDE OF CERRO 

TETAS DE CABRA, CA. 3 M. ELEV. SAND BEACH 

CA. 10 M. INLAND~FHOM HIGH TIDE LINE, COV- 

SSAGE CA. 15%. CATTLE GRAZING. 10 NOVEMBER 

196if 22 

2. PLOT 2. ENSBNADA SAN FRANCISCO, CA. $ KMS. 

BY ROAD EAST OF BAHIA SAN CARLOS ABD CA. 

1/2 KM. INLAND (NORTH) FROM SHORE, CA7~8 M. 

ELEV. MESA-LIKE RIDGE CREST. ROCKY SOIL, 

KITCHEN MIDDENS SCATTERED ON SURFACE. COV 

ERAGE 35% CATTLE GRAZING. 12 JANUARY 1965• • • 26 

3* PLOT 3* ENSENADA SAN FRANCISCO, CA. 5 KMS. 

BY ROAD EAST OF BAHIA SAN CARLOSTJID CA. 

1/2 KM. INLAND (NORTH) FROM SHORE, CA. 5 M. 

ELEV. SWALE, FINE TEXTURED AND DEEP SblL. 

COVERAGE CA. 80*. CATTLE GRAZING. 12 JANUARY 

1965 29 

i+« PLOT J*. CA. 1 KM. SOUTHEAST OF MOUTH OF CANON 

NACAPULETiND CA. 6 KMS. NORTHEAST OF BAHIA 

SAN CARLOS, CXT 60 M. ELEV. UPPER BAJADA. 

ROCKY-LOAM SOIL WITH MUCH GRAVEL AND SAND, 

COVERAGE CA. 50%. CATTLE GRAZING. 13 JANUARY 

1965 . . 7" 37 

5. PLOT 5. SOUTH END OF PUNTA PARADONES, BAHIA 

SAN CARLOS, CA. 30 M. ELEV. RHYOLITE BEDROCK, 

VERY LITTLE SSb SHALLOW SOIL, CA. 3 TO 5 M. 

BELOW MESA RIDGE-CHEST, FACINGTAY. SLOPE 15- 

17jf, COVERAGE CA. 35%» 1^ JANUARY 1965 . . • • **3 

6. PLOT 6. CA. 1.2 KMS.NORTH OF BAHIA SAN CARLOS 

AT CA. lM M. EAST OF ROAD TO ALGADONES, CA. 

25 E7 ELEV. HILLSIDE CA. 15 M. ABOVE VALLEY, 

EAST SIDE OF VALLEY. SSCXY SOIL. EXPOSURE 

SOUTHWEST, 245°, SLOPE 35%» COVERAGE CA. 60%. 

Ik JANUARY 1965 

vlll

LIST OF TABLES—Contlrafd 

TABLE PAGE 

?. PLOT ?. CA. I KM. NORTH OF BAHIA SAM CARLOS 

AT CA. 177 KM. VEST OF ROAD TO ALGADONK3, CA. 

30 FTT SLSV. HILLSIDE AT FOOT OF ESCARPMENT 

AND CA. 25 M. ABOVE VALLEY, VEST SIDE OF 

VALUS?. DEEP ROCKY SOIL. EXPOSURE EAST, 90°, 

SLOPE yft. COVERAGE 100*. SLIGHT CATTLE 

GRAZING. 14 JANUARY 1965 1*9 

8. PLOT 8. CANON NACAPULE. CANYON BOTTOM AT CA. 

1/2 KM. VEST OF MOUTH OF CANYON, CA. 130 17 

ELEV* GRAVEL AND SAND SOIL, DEEP,"AND VITH 

MUCH HUMUS AND ROCK. CATTLE GRAZING. COVER 

AGE CA. 98*. 13 JANUARY 1965 55 

9. PLOT 9« BAHIA SAN PEDRO, BEACH AT CENTER OF 

BAY, CA. 0-1.5 M. BLEV. ABOVE HIGH TIDE LINE. 

VEST EXPOSURE, SLOPE CA. 5** BEACH SAND. COV 

ERAGE CA. 2*. 11 NOVEHEEH 196^ 69 

10. PLOT 10. BAHIA SAN PEDRO, WINDWARD SLOPE OF 

BEACH DUNE AT CENTER OF BAY, CA. 1.5-2.5 M. 

ELEV. ABOVE HIGH TIDE LINE. VE3T EXPOSURE, 

SLOPE CA. 15-20*. BEACH SAND. COVERAGE CA. 

llUbVEMBER 1965 . . . . . 70 

11. PLOT 11. BAHIA SAN PEDRO, CREST AND LEE SIDE 

OF BEACH DUNE AT CENTER OF BAY, CA. 3*5-5 M. 

ELEV. ABOVE HIGH TIDE LINE. BEAClTSAND. COV 

ERAGE £A. 33*. 11 NOVEMBER 1965 72 

12. PLOT 12. BAHIA SAN PEDRO, CA. 1/2 KM. INLAND 

(NORTHEAST) FROM SHORE AT HORTH END OF BAY, 

CA. 12-15 M. ELEV. ROCKY HILL, VOLCANIC ROCK 

AlD SHALLOW SOIL. SOUTH EXPOSURE 170-175°. 

SLOPE 46*. COVERAGE ££. 50*. 19 JANUARY 1965 • 77 

13. PLOT 13* BAHIA SAN PEDRO, CA. 1/2 KM. INLAND 

(NORTH) FROM SHORE AT NORTITEND OF BAY, CA. 

8 H. ELEV. PEDIMENT OF VOLCANIC ROCK WITH FEW 

SHALLOW POCKETS OF SOIL. NORTHWEST EXPOSURE, 

330°, SLOPE 12*. COVERAGE CA. 35*. 19 JANUARY 

1965 80 

ix

LIST OP TABLES—Continued 

TABLE PAGE 

Ik. PLOT l*f. BAHIA SAN PEDRO, CA. 1 KM* INLAND 

(EAST) FROM NORTH END OF BA?, CA. 8 M. ELEV. 

FLOODPLAIN. SANDY-LOAM SOIL Nil TRANSPORTED 

ROCK. COVERAGE CA. 80jf. 1? JANUARY 1965 .... 83 

15. PLOT 15* BAHIA SAN PEDRO, CA. 1 KM. INLAND 

(EAST) FROM SOUTH END OF BA?, CA. 30 M. ELEV. 

BOTTOM OF DEEP CANYON WITH EASIEST AXIS, 

CANYON FLOOR CA. 5 M. WIDE. GRAVEL SOIL AND 

EXPOSED VOLCAUTC BEDROCK. COVERAGE GA. 85*. 

11 NOVEMBER 1965 "T . . . . . 87 

16. PLOT 16. ISLA SAN PEDRO NOLASCO, EAST-CENTRAL 

SIDE, CA. 100 M. ELEV. NORTH EXPOSURE, 3**0- 

360°, SLOPE SOIL LOOSE, ROCKY, RELATIVELY 

DEEP, AND WITH MUCH HUMUS. COVERAGE CA. 95%t 

INCLUDING GRASSES AND FOBBS, CA. 5% EXCLUDING 

GRASSES AND FOBBS. 18 JANUARYT965 98 


SIDE, CA. 11*0 M. ELEV.EAST EXPOSURE, 95°, SLOPE 

1*8£. IZRTSE ROCK WITH SHALLOW SOIL. COVERAGE C£. 

1*0$. 18 JANUARY 1965 101 


SIDE, 270 M. ELEV. (CA. 25 M. BELOW CREST.) 

EAST EXPOSURE, 105 o ,TL0PE 57*. SHALLOW ROCKY 

SOIL. COVERAGE CA. 35*. 18 JANUARY 1965 • • • • 105 

19. PLOT 19. ISLA SAN PEDRO NOLASCO, WEST-CENTRAL 

SIDE, CA. 270 M. ELEV. (CA. 25 M. BELOW CREST.) 

SOUTHWEST EXPOSURE, 235°7"SLOPE 58£. SHALLOW 

ROCKY SOIL. COVERAGE 20£. 18 JANUARY 1965 • • • 109 

20. PLOT 20. ISLA SAN PEDRO NOLASCO, RIDGE-CREST, 

CA. 300 M. ELEV. NEARLY LEVEL TERRAIN. ROCKY 

SOIL. COVERAGE CA. 50*. 18 JANUARY 1965 .... 112 

21. PLOT 21. PUNTA BAJA, CA. 1 KM. NORTH OF MOUTH 

OF ESTERO. SHIFTING BUCH DUNE CA. 12 M. HIGH, 

NEAR CREST. COVERAGE CA. 15*. 17 FEBRUARY 

1965 7 119 

X

LIST OF TABLES—-Continued 

TABLE PAGE 

22. PLOT 22, PUNTA BAJA, CA. 1 KH. INLAND (EAST) 

FBOM SHOHE. SALINE FALT BETWEEN LOW STABI 

LIZED DUNES. HABD-PACKED AND FINE-TEXTURED 

SANDY-SILT SOIL, COVERAGE C±.15*. 17 

FEBRUARY 1965 122 

23* PLOT 23* PUNTA BAJA, CA. 1.5 KMS. INLAND 

(EAST) FROM SHORE. SASDY HUMMOCK OR LOW 

STABILIZED DUNE. COVERAGE CA. 50$ • CATTLE 

GRAZING. 17 FEBRUARY 1965 12*1 

Zk. PLOT 24. CA. ^ KMS. INLAND (EAST) FROM SHORE 

AT 8 KMS."UOHTH OF PUNTA BAJA. DESERT PLAIN, 

HABD-PACKED SILT-LIKE ALLUVIAL SOIL. COVER 

AGE CA. 95%% CATTLE GRAZING. 17 FEBRUARY 

196^7". . 129 

25. PLOT 2 5. ENSENADA BLANC A, ISLA TIBURON, CA. 

100 M. INLAND (EAST) FROM SHOREy CA. 15-^0 

" M. ELEV. ROCKY HILLSIDE FACING SEA, WEST 

EXPOSURE, 295° t SLOPE 32*. 29 JANUARY 1965* • 172 

26. PLOT 26. ENSENADA BLANCA, ISIA TIBURON, CA. 

150 M. INLAND (EAST) FROM SHORE, CA. 22 M. 

ELEV. MESA-LIKE RIDGE-CREST. 29 JANUARY 

1965 173 

27. PLOT 27. ENSENADA BLANCA, ISLA TIBURON. CA. 

1/2 KM. INLAND (EAST) FROM SHORE, CA. 6 Tf7 

ELEV. NARROW FLOODPLAIN IN BROAD CXJfYON, 

ROCK, GRAVEL, AND SAND SOIL. 30 JANUARY 1965* 1?6 

28. PLOT 28. ENSENADA BLANCA, ISLA TIBURON, CA. 

1/2 KM. INLAND (EAST) FROM SHORE, CA. 15^0 

M. ELEV. SOUTH EXPOSURE, 195-215°,~LOPE 38^. 

ROCKY, SOUTH-FACING SLOPE OF BROAD CANYON. 

29 JANUARY 1965 • 179 

29. PLOT 29. ENSENADA BLANCA, ISLA TIBURON, CA. 

1/2 KM. INLAND (EAST) FROM SHORE, CA. 15-20 

M. ELEV. NORTH EXPOSURE, 20°, SLOPE 38*. ROCKY 

NORTH-FACING SLOPE OF BROAD CANYON. 29 JANUARY 

1965." 181 

30. PLOT 30. PALO FIERRO, ISLA TIBURON, CA. 1.5 

KMS, INLAND (WEST) FROM SHORE, CA. 81, ELEV. 

LOW FLAT-TOP RIDGE, DESERT PAVEMENT OF TRANS 

PORTED FELCITE. COVERAGE CA. 6$. Ik FEBRUARY 

1965 "T 189 

xi

LIST OF TABLES—Continued 

xii 

TABLE PAGE 

31. PLOT 31- PALO FIEBBO, ISLA TIBURON. CA. 1,5 

KM3. INLAND (WEST) FROM SHORE CA. O WT ELEV. 

LEVEL TERRAIN IN SWALE BETWEEN DESERT PAVE 

MENT RIDGES. SILTY-SAND SOIL. COVERAGE CA. 

80^. 14 FEBRUARY 1965 • • • • 190 

32. PLOT 32* PALO FIERRO, ISLA TIBURON, CA. 1 

KM. INLAND (WEST) FROM SHORE, CA. 5 KT ELEV. 

LEVEL TERRAIN, SANDY SOIL. COVSSAGE CA. 25%» 

15 FEBRUARY 1965 7". . • . 19** 

33• PALO FIEBRO, ISLA TIBURON, CA. 1/2 KM. INLAND 

(WEST) FROM SHORE. COMMON AS50Y0 MARGIN 

SPECIES IN COAST SHRUB ZONE (FRANKSNIA). 15 

FEBRUARY 1965 196 

3if. PLOT 33* PALO FIERRO, ISLA TIBURON, CA. 2*5 

KMS. INLAND (WEST) FROM SHORE, CA. 30 M. ELEV. 

LEVEL TERRAIN. ROCK. GRAVEL, AND LOAM SOIL. 

COVERAGE CA. 50jf. ik FEBRUARY 1965 200 

35. PLOT 34. PALO FIERRO, ISLA TIBURON, CA. 4 KMS. 

INLAND (WE3T) FROM SHORE, CA. 50 M. ELEV. 

LEVEL TERRAIN, BAJADA. GRATSLLY SOIL. COVER 

AGE CA. 50^. 14- FEBRUARY 1965 202 

36. PLOT 35* PALO FIERRO, ISLA TIBURON, CA. 4 KMS. 

INLAND (WEST) FROM SHORE, CA. 50 M. ELEV. 

LEVEL TERRAIN WITH SMALL SHALLOW WASHES. SAND 

AND GRAVEL SOIL. COVERAGE CA. $$$• 14 FEBRUARY 

1965 7" 204 

37. PLOT 36. SAUZAL, ISLA TIBURON, CA. 1/4- KM. 

EAST OF ARROYO SAUZAL AT CA. 3 K&S INLAND 

(NORTH) FROM SHORE, CA. 25 M. ELEV. TOP OF 

LOW ROLLING HILL. ROC?, GRAVEL, AND LOAM SOIL. 

COVERAGE CA. 15*. 31 JANUARY 1965 ...... 215 

38. PLOT 37. SAUZAL, ISLA TIBURON, CA. 1/2 KM. 

EAST OF ARROYO SAUZAL AT CA. 3 KMS. INLAND 

(NORTH) FROM SHORE, CA. 3$~~M. ELEV. TOP OF 

LOW ROLLING HILL. LlSliT-COLORED SMALL LOOSE 

ROCK AND FINE-TEXTURED SOIL. 31 JANUARY 

1965 216

LIST OP TABLES—Continued 

xlll 

TABLE PAGE 

39. PLOT 38* SAUZAL, ISLA TIBUROH, CA. 1/2 KM. 

EAST OF ARROYO SAUZAL AT CA. 3 KMS. INLAND 

(NORTH) FROM SHORET CA. 4LT"M. ELEV. SMALL 

ROCKI HILL, NORTH ENSURE, 15°. SLOPE 24*. 

COVERAGE CA. 30*. 31 JANUARY 19*5 219 

40. PLOT 39* SAUZAL, I SLA. TIBURON, CA. 1/2 KM. 

EAST OF ARROYO SAUZAL AT CA. 3 KLFE. INLAND 

(NORTH) FROM SHORE, CA. 4?TM. ELEV. SMALL 

ROCKY HILL, SOUTH ENSURE, 205°, SLOPE 43*. 

COVERAGE CA. 10*. 31 JANUARY 1965 221 

41. PLOT 40. ARROYO SAUZAL, ISLA TIBURON, CA. 3 

KMS. INLAND (NORTH) FROM SHORE, CA. ZFLTM 

ELEV. ROCK, GRAVEL, AND SAND SOLET COVER 

AGE CA. 70JL. 31 JANUARY 1965 224 

42. PLOT 41. UPPER CENTRAL VALLEY, ISLA TIBURON, 

CA. 200 M. ELEV. VALLEY PLAIN, PINE-TEXTURED 

SOIL WITH MUCH ROUGH GRAVEL AND SMALL ROCK. 

1 FEBRUARY 1965 • • • 233 


CA. 200 M. ELEV. VALLEY PLAIN, COARSE GRAVEL 

USD ROCK SOIL. COVERAGE CA. 20*. 2 FEBRUARY 

1965 236 


CA. 200 M. ELEV. ARROYO, GRAVELLY SAND SOIL. 

COVERAGE CA. 80*. I FEBRUARY 1965 ...... 239 

45. PLOT 44. ARM OP SIERRA MENOR AT UPPER CENTRAL 

VALLEY, ISLA TIBURON, CA. 300 M. ELEV. EAST 

EXPOSURE, 95°, SLOPE 23>. ROCK&OPES WITH 

SHALLOW POCKETS OP SOIL. COVERAGE CA. 50*. 

2 FEBRUARY 1965 • • • 245 

46. PLOT 45. ARM OF SIERRA MENOR AT UPPER CENTRAL 

VALLEY, ISLA TIBURON, CA. 450 M. ELEV. EAST 

EXPOSURE, 70O, SLOPE 2L£. ROCK SLOPES WITH 

SHALLOW POCKETS OP SOIL. COVERAGE CA. 50#. 

2 PEBRUARY 1965 247


xiv 

TABLE PAGE 

47. PLOT 46. TECOMATE, ISLA TIBUBON, CA. 1.5 KMS. 

INLAND (SOUTS) FBOM SHOBL,CA.15 M. ELEV. 

VALLEY PLAINS BOCK, 03*1|A*»TAID LOAN SOIL. 

COVERAGE 0^4 10** 12 FEBRUARY 1965 .. . . . . . 255 

48. PLQT 47* TECOMATE, ISL* TIBURON, CA. 1 KM* 

INLAND (SOUTH) FBOM SNOBB; 0JU 12TI. ELEV. 

? VALLEY PLAIN, ROCKY LOAMSOIL, COVERAGE CA. 

$5$+ 13 FEBRUARY 1965* • • .......... 256 

49. PI FEBRUARY 1965* • • • • • 287 

54. PLOT 53* ISLA SAN ESTEBAN, CA. 1 KM. INLAND 

(WEST) FROM EAST-CENTRAL SHOTS, CA. 60-70 M. 

ELEV. SOUTH EXPOSURE, 190-200®, SCOPE 

SCORIAE AND SHALLOW SOIL. COVEBAGE CA. 15*. 

27 FEBBUABY 1965 289


TABLE PAGE 

55* LIST OF SPECIES ALONG CA. 1/2 KM. OF STRAND, 

SANTA ROSA (MAINLAND), SOUTH STRAND PENINSULA 

BETWEEN ESTERO AND SEA. LOW AND PARTIALLY 

STABILIZED BEACH DUNES, CA. 2-4 M. ELEV. 

COVERAGE CA. 25*. 16 FEBRUARY 1965 317 

56. PLOT 5^. ESTERO AT SANTA ROSA (MAINLAND), 

SHALLOW TIDAL SEA WATER AND WET SALINE SOIL, 

COVERAGE CA, 98*. 16 FEBRUARY 1965 319 

57. PLOT 55. SANTA ROSA (MAINLAND), CA. 150 M. 

INLAND (EAST) FROM ESTERO, CA. 2"X ELEV. 

LOWER BAJADA, SANDY PLAIN, AVERAGE CA. 30*. 

16 FEBRUARY 1965 323 

58. PLOT 56. SANTA ROSA (MAINLAND), CA. 1/2 KM. 

INLAND (EAST) FROM ESTERO SHORE,UA. 8 M. ELEV. 

LOWER EDGE OF MIDDLE BAJADA, SANDY"PLAIN. 


59. PLOT 57. SANTA ROSA (MAINLAND), CA. 2 KMS. 

INLAND (EAST) FROM ESTERO SHORE, CA. 15 M. 

ELEV. MIDDLE BAJADA, GRAVELLY-SAND PLAIN. 


60. PLOT 58. SANTA ROSA (MAINLAND), CA. 3 KMS. 

INLAND (EAST) FROM ESTERO SHORE, ""CA. 30 M. 

ELEV. UPPER BAJADA, GRAVELLY-SAND PLAIN, 


61. PLOT 59. SANTA ROSA (MAINLAND), CA. 3»5 KMS. 

INLAND (EAST) FROM ESTERO SHORE, CA. 40-55 M. 

ELEV. HILL, 20 M. HIGH, REDDISH VOLCANIC ROCK, 

SHALLOW SOIL, SOUTHWEST EXPOSURE, 220°, 

SLOPE 27*. COVERAGE CA. 15*. 15 FEBRUARY 1965. 338 

62. PLOT 60. SARGENTO, CA. 1/2 KM. INLAND (NORTH) 

FROM SHORE AT ESTERO, CA. 2 M. ELEV. LOWER 

BAJADA, FINE-TEXTURED SILT-LIKE SALINE SOIL. 

COVERAGE CA. 30*. 19 FEBRUARY 1965 ...... 343 

63. PLOT 61. SARGENTO, CA. 1.5 KMS. INLAND (NORTH) 

FROM SHORE AT ESTERS7 CA. 15 M. ELEV. MIDDLE 

BAJADA, DECOMPOSED GRAtflTIC GRAVEL AND SAND 

SOIL. COVERAGE CA. 20*. 18 FEBRUARY 1965 ... 344 

XT


TABLE PAGE 

xvi 

64. PLOT 62. SARGENTO, CA. 2.5 KMS. INLAND (NOBTH) 

FROM SHOBE AT ESTEBO, CA. 40 M. ELEV. LOW AND 

VIDE FLAT-TOPPED RIDGE IN UPPER BAJADA. ROCKY 

SOIL. COVERAGE CA. 15%. 19 FEBRUARY 1965 • • • 346 

65* PLOT 63. SABGENTO, CA. 2«5 KMS. INLAND (NOBTH) 

FROM SHORE AT ESTER57 CA* 25 M. ELEV. UPPER 

BAJADA, DECOMPOSED GRANITIC GRAVEL AND SAND 

SOIL. COVERAGE CA. 15*. 18 FEBRUARY 1965 • • • 34? 

66. PLOT 64. SARGENTO, CA. 3 KMS. INLAND (NORTH) 

FROM SHORE AT ESTEROT CA. 70 M. ELEV. SMALL 

GBANITE HILL NEAB SOOTS"SIDE OF CEBBO TEPOPA. 

SOUTH EXPOSURE, SLOPE 22*. COVERAGE CA. 15*. 

19 FEBBUABY 1965 3^9 

67. SUMMARY OF HABITATS, COMMUNITY INDICATOBS, AND 

NUMBEBS OF SPECIES IN QUADBATS AND COMMUNITY 

STANDS. SEE FIGS. 83 AND 84 365 

68. NUMBEB OF SPECIES AND AREA OF SONOBAN ISLANDS 

IN THE GULF OF CALIFORNIA 378 

69. DISTRIBUTION OF LIFE-FORMS IN GULP COAST OF 

SONOBA . . . 382 

70. LIFE-FORM DISTRIBUTION AT TWO STATIONS ON 

ISLA TIBUBON 401 

71. LIFE-POBM SPECTRA OF THREE COMMUNITY STANDS 

AT CENTRAL VALLEY STATION, ISLA TIBUBON. . . . 404 

72. LIFE-FORM SPECTBUM ACROSS ENVIBONMENTAL 

GRADIENTS AT SANTA ROSA, INFERNILLO REGION . . 408

LIST OP FIGURES 

FIGURE PAGE 

1* Map of study area * * * * 2 

2* Upper strand | at base of northwest side of 

Cerro Tetas de Cabra. * 21 

3* Aerial rlcw of Sierra Naoapule 24 

4* Diagrammatic representation of alluvial plain 

oa« 5 lots, east of Bahla San Carlos • * • • • 25 

5, Desert plain or flat-topped ridge at oa* 5 

kms. east of Bahla San Carlos and oa. i/2 

km* Inland from shore 28 

6. Swale or dralnageways through desert plain 

at oa* 5 kms* east of Bahla San Carlos and 

oa* i/2 km* inland from shore *••••••• 32 

7* Tillandsla exserta* at oa* 5 kms* east of 

Bahla San Carlos and oa* 1/2 km* inland 

from shore 35 

8* Upper bajada oa. 1 km* southeast of Canon 

Naoapule. *** *••••••••• 39 

9* Aerial view of rhgollte hills between Bahfa 

San Carlos and Canon Naoapule *••••*•• 41 

10* Southwest-facing slope oa* 1*2 kms* north 

of Bahla San Carlos ••*••••••.••• 48 

11. Canon Naoapule* ••••*••••• 54 

12* Aerial view of Bahla San Pedro* * *••••• 64 

13* Thomsorub near Pioo de Guaymas * 66 

14* Windward side of beaoh dunes at Bahfa San 

Pedro * 68 

15* Crest of low beaoh dune» Bahfa San Pedro* * * 73 

xvll 

4

LIST OF PIGUHES--Continued 

xvlll 

FIGURE PAGE 

16 • Early fall aspect of upper toajada at Bahfa 

San Pedro 75 

17* South-facing slope at north end of fiah£a 

San Pedro • •«•*•••••• 79 

18 • Flood plain oa. 2 kms* Inland from shore at 

Bahia San Pedro *•••••••• 85 

19* Canyon at south end of Bah£a 3an Pedro* • • • 89 

20. East side of Isla San Pedro nolasoo seen 

from Bahia San Pedro. **•••••••••• 92 

21. Aerial view of east side of Isla San Pedro 

Nolasoo • •••«•*•••••••••••• 93 

22* Northeast side of Isla San Pedro Nolasoo* • • 99 

23* Northeast side of Isla San Pedro Nolasoo* • • 102 

24* Northeast side of Isla San Pedro Nolasoo* * * 103 

25* Northeast side of Isla San Pedro Nolasoo* * * 104 

26* East slope at orest of Isla San Pedro 

Nolasoo ••*•••••••••••«•••• 106 

27* Northwest side of Isla San Pedro Nolasoo* * * 108 

28* Northwest side of Isla San Pedro Nolasoo 

near orest* *•••••••••• 110 

29* Aerial view of coastal dunes several kilometers 

north of Punta Baja* *•••••••• 118 

30* Cardonal at Punta Baja, oa. 1 km. Inland 

(east) from shore •• ...... 125 

31* Aerial view of mesqultal several kilometers 

north and Inland (east) from Punta Baja * * • 128 

32* Saltbush flats at edge of the mesqultal at 

oa* 8 kms* north and oa* 4 kms* Inland 

Toast) of Punta Baja *•*••••• 131

LIST OF FIGUBES—-Continued 

xlx 

FIGURE PAGE 

33. Aerial view of Isla Aloatrazi looking northwest 

* 135 

34* Isla Aloatraz, looking west from sandy flat 

at east end of Island 136 

35* Southwest side of Isla Aloatraz. • •••••• 1^3 

36. Cormorant rookery on northeast-faolng slope 

on east side of mountain, Isla Aloatraz, at 

oa. 135 »• ©lev. • ••••••••••«••• 144 

37* Southeast side of Isla San Pedro Nartlr* • • . 152 

38* Northwest side of Isla San Pedro Hartlry 

about 100-120 m* elev • • • 153 

39* Mesa at Ensenada Blanoa, Isla Tlburon* • • • • 174 

40. Aerial view showing bajada at east-oentral 

side of Isla Tlburon *•••••••••••• 185 

41. Coast shrub (Frankenla) zone at Santa Rosa, 

Isla Tlburon * * • * * I87 

42* Swale In lower bajada, Palo Flerxo, Isla 

Tlburon 192 

43• Lower bajada, Palo Flerro, Isla Tlburon* • • • 195 

44* Middle bajada, several,kilometers west of 

Santa Rosa, Isla Tlburon 199 

45* Upper bajada, east foothills of Sierra 

Kunkaak at several kilometers west of 

Santa Rosa, Isla Tlburon ••••••••••• 207 

46* East foothills of Sierra Kunkaak, west of 

Santa Rosa, Isla Tlburon ••••••••»•* 209 

47* Bast foothills of Slerga Kunkaak, west of 

Santa Rosa, Isla Tlburon* South-faolng 

slope ••••• * 210 

48. East foothills of Sierra Kunkaak, west of 

Santa Rosa, Isla Tlburon 212

LIST OF FIGURES—Continued 

FIGUBE PAGE 

49* Aerla^ view of south-oentral side of Isla 

Tiburon showing Arroyo Sauzal . . • . 213 

50* Sauzal waterhole, Isla Tiburon 226 

51, Sauzal waterhole, Isla Tiburon 227 

52. Upper end of central valley, Isla Tiburon • . • 231 

53* Upper end of central valley, Isla Tiburon • • • 23*t 

5^« Upper end of oentral valley, Isla Tiburon . • . 24-1 

55* Upper end of oentral valley, Isla Tiburon* 

Olneya tesota along old arroyo bed 2*4-2 

56. Upper oentral valley, Isla Tiburon. Looking 

northeast from arm of Sierra Menor• ...... 249 

57* Looking east from arm of Sierra Henor range m 

adjacent to upper oentral valley, Isla Tiburon. 250 

56. Arm of Sierra Menoaj, west of upper oentral 

valley, Isla Tiburon •••••• 252 

59* Aerial view of Isla San Esteban ••»••••• 269 

60. Aerial view of Isla San Esteban •••••.•• 270 

61. Lower portion of oentral valley, Isla San 

Esteban 27 5 

62. Eohlnooereus grandIs on Isla San Esteban. ... 276 

63. East-oentral shore of Isla San Esteban at 

lower end of oentral valley •••••••••• 281 

64. Central valley, Isla San Esteban. ....... 285 

65. Aerial view showing Isla Datil,#Isla Cholludo, 

and the south end of Isla Tiburon ...•••• 293 

66. Isla Datll. Small oanyon near shore at 

northwest side of Island. ••••••••*•• 299 

XX

LIST OF FIGURES--Continued 

xxl 

FIGURE PAGE 

67. Isla Cholludov showing east side of island. • 303 

68* Looking north from Isla Cholludo towards 

the south shore of Isla Tiburon 305 

69 • Northeast side of Isla Cholludo • •••••• 306 

70. Succulent growth on northeast side of Isla 

Cholludo 307 

71 . Aerial view of Infemillo channel 311 

72m Aerial view of middle bajada on mainland side 

of Infemillo, at several kilometers north 

of Punta Chueoa Jib 

73, Aerial view of mangroves in estero at Santa 

Rosa (mainland) ••••• 321 

Mangroves at Santa Rosa (mainland) 322 

75* Lower bajada at Santa Rosa (mainland) . . • . 32*t 

76* Lower middle bajada, Santa Rosa (mainland)* • 328 

77* Upper middle bajada, Santa Rosa (mainland). • 334 

78* Upper bajada, Santa Rosa (mainland) . . • • • 335 

79• Upper bajada, Santa Rosa (mainland) 336 

80. Isla Patos (19^6) 352 

81* Isla Patos (19^6) 353 

82. Isla Patos (19^6) 35^ 

83. Isla Patos (196*0 356 

84. Frequency distribution of three oommon species 

at Santa Rosa, Infemillo Region. ...... 362 

85. Frequency distribution of three oommon speoies 

at Santa Rosa, Infemillo Region. •••••• 363

LIST OP PICrUBES—-Continued 

xxii 

FIGURE PAGE 

ru i 

86* Maximum number of speoies occurring in 

quadrats and in oommunity stands at the 

study areas on the major islands and 

mainland of the Gulf Coast ••••»•••• 375 

87* Regression of numbers of speoies on total 

area for the islands of Sonora in the Gulf 

of California. ••••••••••••••• 379 

88. Life-form speotra on islands and Gulf Coast 

of Sonora 383 

89• Life-form speotra at Ensenada Blano$ and 

central valley stations, Isla Tiburon. • • • 402 

90• Life-form speotra of three communities at 

oentral valley station, Isla Tiburon • • • • *K>5 

91. Life-form speotra of three communities at 

oentral valley station, Isla Tiburon • • • • kO6 

92. .Life-form distribution at Santa Rosa, 

Infemillo Region* 409

ABSTRACT 

An eoologioal and distributional analysis is given 

for the natural desertsorub and thornsorub vegetation on 

the islands of Sonora in the Gulf of California, Mexloo, 

and on the adjaoent mainland of Sonora between Punta Sar- 

gento and Guaymas-Empalme • Isla Tlburon, the largest island 

in the Gulf of California, is in this study area and its 

flora and vegetation as investigated sinoe 195** are treated 

in detail. In addition to analysis of the flora and vege 

tation the insular reptilian and mammalian faunas are 

reported for Isla Tiburon and eaoh of its four satellites-- 

Islas San Esteban, Datil, Cholludo, and Patoa—and for the 

other major Sonoran islands, viz,, Isla San Pedro Martir, 

Isla San Pedro Nolasoo, and Isla Aloatraz* The eoologioal 

and geographioal distribution of speoies and their life- 

forms are disoussed, and an analysis of the oontinuum and 

mosaio patterns assooiated with continuous and discontin 

uous environmental gradients is given* Speoies, life-forms, 

oommunities, oontinua, and mosaics in the desertsorub of the 

Sonoran Desert in northwestern Hexloo are disoussed in rela 

tion to oonoepts pertaining to the nature and evolution of 

natural oommunities. 

xxiii

INTRODUCTION 

The region treated in the present study lies entirely 

within the state of Sonora, Mexico. The primary area of 

study extends from the vicinity of Guaymas in the south to 

the north end of the Estreoho Infernlllo in the vicinity of 

Punta Sargento (=Sargent's Point) and includes the adjacent 

Sonoran islands (Fig* 1). All of the islands politically 

in Sonora are covered in the present work except Isla 3an 

Gorge, some of the rocks and isles in the vicinity of 

Guaymas and Bahfa San Carlos, and the sand-bar islands 

along the southwest coast of Sonora. The objective has 

been the eluoidatlon of blotio communities of the region 

as exemplified by the natural vegetation. An attempt has 

been made to include the coastal margin of the mainland 

regions up to the summit of the coastal mountains or the 

coastal plains to about 15 kms inland from the shore, and 

the entire area of the islands. The study area lies 

between lat. 27°50* N. and 29°22* N., equivalent to 

1. Isla San Gorge («Saint George or George Island) 

is situated near the head of the gulf at lat. 31°01 , j longitude 

l^ 0 ^* (see van Hossem 19^5* and Tamayo, 19*1-9). It 

Is a guano-covered bird rookery with a single known species 

of vascular land plant, Chenopodium murale (Johnston, 192*0. 

1

Figure 1. Map of study area.

C»rro Lobot 361 

A~ p Llbtrtad 

s 

y/V- \ 

V^-fi 

^DtinnbaqM 

XV 

rfei /*v 

vJipopa SSS^v 

Pun fa Sargintdf „ - \ut /VN 

l«lo Pofo.O 

A1025 Pico Johnion 

approximately 175 kms. There are, of course, large areas 

within it whioh I have not been able to oover. 

From the standpoint of a biologist one of the most 

attractive features of the Gulf Coast of Sonora is the 

relatively natural and undisturbed state of the biota. 

The influences of man are still minimal over the greater 

part of the area. The islands, with minor exceptions, are 

virtually undisturbed. The indigenous people, the Seri 

Indians, have greatly dwindled in number and today have 

vacated much of the original area they onoe occupied 

(Kroeber, 1931; Moser, 1963)* They were, and still 

largely are, a seafaring people that augmented their sus 

tenance by some terrestrial hunting and gathering, but did 

not practloe agriculture (McGee, 1896, 1898; Kroeber, 1931; 

Moser, 1963). 

Much of the area around Guaymas has been altered 

by urbanization and centuries of grazing and woodcutting, 

yet there are remarkably undisturbed sites within easy 

access of the city. Bahfa San Carlos, once a favorite 

spot for scientists and nature lovers has been greatly 

decimated within the last decade by "developers." The 

great coastal plains south of Guaymas and west of Hermo- 

sillo (Llanuras de San Juan Bautista) have been largely 

converted into irrigated fields and little remains of 

the original vegetation except along the immediate coast. 

3

Due to the ever inoreasing population pressure in Mexico 

it is not realistic, however, to expect the rest of the 

region to remain in this primeval state. A conservation 

plea is made here to preserve the natural islands and pro 

hibit their exploitation. Such action would be of no 

economic hardship to anyone and would provide irreplace 

able resources for future study. 

Biologically the east side of the Gulf of Cali 

fornia has long remained a poorly known area. Major 

references to the flora and vegetation include works by 

Watson (1889), Johnston (192*0, Gentry (19^9)» Shreve 

(195l)» and Wiggins (196*0. A more complete reference to 

earlier works will be found in Johnston (1924) and Gentry 

(19^9)• By far the most exhaustive and thorough work on 

plants of the Gulf of California to date is Johnston's 

paper (192*1-). His insight and keen observations and 

interpretations were based In part on three months of 

"collections, field observations, and subsequent herbarium 

studies" (Johnston, 1924, p. 951)* Watson's 1889 paper 

treats the collection made by Dr. Edward Palmer in 1887 

and was the source of many new taxa. Shreve's works on 

the vegetation of northwestern Mexico provide the classical 

background to all vegetation studies In this region. In 

recent years Drs. Wiggins and Moran have collected on the 

islands and shores of the Gulf of California but their

efforts have been oonoentrated more on the west side of 

the gulf rather than on the east side. Various other 

papers have been published on aspects of plant life in 

the gulf, but sinoe these are generally specialized works 

and only incidentally include the Gulf Coast of Sonora, 

most of them are not dealt with here. 

No single modern referenoe oovers the herpetology 

of the islands of the Gulf of California and the mainland 

of Sonora. Herpetological references for the islands and 

Gulf Coast of Sonora inolude works by Allen (1933)* Bogert 

(19^5) i Bogert and Oliver (1945), Cliff (1954), Dixon 

(1964), Lowe (1955)» Lowe and Norris (1955). Klauber 

(1940), Soule (1966), Shaw (1945). Smith and Taylor (1945. 

1948, and 1950), Taylor (1936), Van Denburgh (1922), and 

Zweifel and Norris (1955)* 

The mammalian fauna of the islands and Sonora, for 

the most part, has not been oritioally reviewed since the 

reports by Burt (1932, 1938)* 

Van Rossem*s monumental work on the avifauna of 

Isla Tiburon (1932) and his distributional survey of the 

birds of Sonora (1945) are of classical importance and 

remain as the primary reference. Additional works of 

Interest here include Phillips and Amadon (1952) and 

Vaurle (1953)- 

5

The Gulf of California and its surrounding area 

is centered in the Paolflo Coast Cordillera and is appar 

ently an extension of the structurally oomplex East Paolflo 

Rise (Runsk and Fisher, 196^)• The Gulf Coast of Sonora 

consists primarily of westward-dipping mid-Tertiary and 

later sediments and voloanlos (Runsk and Fisher, 196*0 • 

The coastal plains south of Guaymas and the Llanuras de 

San Juan Bautista are apparently of recent alluvial and 

deltaio origin (Runsk and Fisher, 1964-) • 

The complex geology of the Gulf Coast of Sonora 

is relatively poorly known due In part to the "masking 

of the older geology by Tertiary volcanic rooks and allu 

vium" (Allison, 196**, p. 5). The middle and upper Tertiary 

volcanic flows, conspicuous through the region, appear to 

rest generally on granodlorite and metamorphlo basements 

(Anderson, 1950i van Andel, 1964; Wilson, 19^9)• The 

granodiorites seem to have their counterparts in the 

granltio rook of Cretaceous age in Baja California. In 

many places granodlorite and metamorphosed rook are 

exposed and without an igneous overlay, Isla Datil, 

Isla San Pedro Nolasoo, Cerro Tepopa, Sierra San Nicolas, 

and a localized area between Bahfa San Carlos and Bahfa 

San Pedro (see Anderson, 1950). This pattern is readily 

evident at Cerro Prleto at the north end of Bahfa Kino 

where most of the surfaoe of the mountain is volcanic in 

6

origin, but at its northern end granite can be clearly 

seen underneath the volcanic cap. On the Sonora coast 

a chain of disjunct granitic mountains extends in a general 

line from north to south (see Fig. 1) as follows: the 

Sierra Libertad range, Cerro Pelon and other mountains 

about Desemboque, Cerro Tepopa, Cerro Prleto, Sierra San 

Nicolas, and Cerro Tastiota. The granodiorite of Isla 

San Pedro Nolasco and the mainland coast opposite it may 

be related to the northern chain but present a somewhat 

different looking topography. 

The regions surrounding the Gulf of California 

have remained generally emergent since post-Cretaceous 

(Allison, 1964). By the end of the Miocene the Gulf of 

California appears to have been present as a narrow trench 

(Wilson, 1949). While it seems beyond all reasonable 

doubt that the Gulf has been present since late Miocene, 

diostrophic movement on the islands and the mainland 

extends from Pliocene to Recent (Anderson, 1950). Slg- 

nifleant shifts in climate, and local movements and 

fluctuations in sea level are evident in Pleistocene and 

Recent times (Anderson, 1950; Allison, 1964; Durham, 1950; 

Gentry, 1949; Parker, 1964; Shepard, 1964). Both warmer 

and colder climatic fluctuations are indicated in the 

Pleistocene: (1) Parker (1964) found shallow water marine 

mollusks dating 17,000 to 19,000 years B.P. at 110 to 115 m

depth* He al$o concluded that the occurrence of cold 

water species implies that during the Pleistocene south 

ward migration of 700 miles or more was possible; (2) 

Durham (1950) reports fossil reef coral genera indicating 

that at one time or more there were intervals during the 

Fleistooene with warmer ollmate than at present* The 

complex topography and relief in the regions surrounding 

the Gulf permit considerable local habitat (elevation and 

slope exposure) selection and would allow the terrestrial 

biota to survive the Indicated moderate climatic changes 

without extinction or macromlgratlon* 

In this work I have not treated the paleo- 

ecologloal picture as the present treatment of the prob 

lem is already oversize* Needless to say the paleo- 

ecological picture for northern Mexico, and more 

particularly western Sonora, is essentially untreated* 

The reoent excellent review of Southwestern paleoecology 

by Martin and Merringer (1965) is typical for studies of 

this region In omitting consideration of northwestern 

Mexico* 

No effort has been made in the present work to 

bring together and analyze cllmatologlcal data on the 

subject* which information can be located in the following 

references: Contreras (19^2), Hastings (196*0, Shreve 

8

(19^)» Wallen (1955 )• I knov of no climatologloal data 

for Isla Tiburon and the other islands inoluded in this 

study. 

9

MATERIALS AND METHODS 

Field investigations in northwestern Mexico have 

been carried out 1uy the author during the past 12 years. 

My first visit to the islands in the Gulf of California 

was made in 195^ when I accompanied Dr. Charles H. Lowe. 

•A' 

More intensive investigations in the Gulf Coast of Sonora 

have been carried out since 1962. A total of 160 days 

have been spent in the region and work was carried out 

during every month of the year on Isla Tibur&i and in the 

Guaymas region. 

Plant taxonomy in the present study does not fol 

low any single work of other authors and reflects my own 

understanding of the flora and my evaluation of the exist 

ing, and quite uneven, literature. The taxonomic problems 

in this region are many and far beyond the scope of the 

present work. By far the most extensive coverage is that 

given by Wiggins (1964). 

Plant material examined in the present study is 

deposited in the Herbaria of the Allan Hancock Foundation 

of The University of Southern California, The University 

of Arizona, The university of California (Berkeley and Los 

Angeles), The California Academy of Sciences, Pomona 

10

College, Hancho Santa Ana Botanic Garden. San Diego Society 

of Natural History, and The Dudley Herbarium (Stanford). 

I am, indeed, grateful to the Curators of these Herbaria 

for their courtesy in allowing me to examine specimens 

under their care. Additional material was collected by 

the author and Dr. Charles H. Lowe during this continuing 

investigation, and it is, therefore, deposited in the 

Ecology Laboratory of the Department of Zoology where it 

has been studied, with duplicates for deposit in The Uni 

versity of Arizona Herbarium. 

All areas for quadrats were selected with intent 

that they be representative of the natural vegetation of 

the Gulf Coast of Sonora. With regard to randomness of 

the quadrats* it is worth noting that anyone can determine 

quadrat sites "randomlyi M but significant representation 

requires familiarity with and an understanding of each 

situation encountered, and quadrat sites were selected 

accordingly. The quadrats are 0.1 hectare in size, being 

50 by 20 m. in dimension, or in some cases they are 1/2, 

1/4, or 1/8 hectare. Such oases are indicated in the 

plant census tables. 

The total number of individuals of each species 

encountered in the quadrat is given, and coverage was 

measured or estimated (see below). Seedlings were not

counted* Herbaceous plants, most of which are ephemerals 

In this region, are listed for presence but usually not 

counted. In addition to the species found within the 

quadrat, those occurring in close proximity to it (esti 

mated still to be within one hectare) and in the same 

stand or community are also listed for presence* The 

total number of speoles in the quadrat and the total number 

present in the stand are clearly indicated* 

Maximum heights of the non-herbaceous species 

present in the stand were measured* A meter stick was 

used for some measurements! most measurements, however, 

were made with a telescoping fiberglass height-pole, 

extendable to 25 feet (7*62 meters)* This height-pole 

is calibrated in feet and tenths of feet* Accordingly 

the data for height given in the tables are in feet rather 

than meters (1 ft* * *30^8 m., 1 m* = 3-280 ft.)* For 

species over 25 feet, of which there are few in this 

region, the height-pole was extended as a guide for esti 

mating the height* Mean height in the plant census tables 

refers to the mean value for a number of the tallest indi 

viduals of that species found In the stand. Usually a 

sample of the ten plants with maximum heights was measured, 

but this was not always possible or practical. . 

12

Plant coverage Is expressed as percentage of ground 

covered by vegetation. In the more open, sparse, and loir 

shrubby desertscrub It was usually measured with a Bitter- 

11oh coverage stlok (Cooper, 195?) and In a few instances 

coverage values are given for Individual species In the 

quadrat. In most cases, however, coverage was estimated 

by sight* 

Number of species in the stand is rcughly equiva 

lent to the number of species in the hectare in which the 

quadrat is situated and in all cases refers to the same 

community type. Percent of slope of the terrain and 

exposure were measured with a Bronton compass. 

In some instances the determination of number of 

individuals per unit area was difficult, as in the cases 

of stolonlferous species, and when branches touch the 

ground and take root. In most; oases, however, the 

determination of the number of Individuals is not unusually 

difficult in desertscrub. 

During the course of the work, beginning in the 

early 1950's, vertebrate species were collected. The 

material is deposited in the Department of Zoology at The 

University of Arizona. The accounts given of the reptilian 

and mammalian fauna of the Sonoran islands is based on 

these collections and on the published reports. 

13

DESCRIPTION AND ANALYSIS OF COMMUNITIES 

For the sake of convenience and out of necessity 

to organize the presentation, I have divided the Gulf 

Coast of Sonora into a number of regions. These follow 

the most prominent physiognomic features including topo 

graphy, geology (see de Czerna, 1961; Mejorado, 1956; van 

Andel and Shor, 1964), and vegetation, and may be regarded 

as biogeographio units. Each island has been treated as a 

separate region and the islands are in faot, to varying 

degrees, geologioally, biogeographioally, and vegetation- 

ally distinct from each other. A significant exception to 

regarding eaoh island as a biogeographio unit is seen in 

comparison of the east side of Isla Tiburon and the oppo 

site mainland shore along the Infernillo channel. These 

two areas appear to represent a single biogeographio 

region. While recognizing such a relationship, I am, how 

ever, discussing eaoh one separately beoause of continuity 

and perhaps the traditional idea of treating eaoh island 

separately. 

Distribution of species known to me in the various 

regions and islands of the Gulf Coast of Sonora are given 

in Appendices A, B, and C for vascular land plants, 

14

amphibians and reptiles* and mammals• In certain oases 

there are strong indications that a species should be 

present In a given region but identifiable speolmens or 

observations may be lacking* In such oases the species 

is indioated by a question mark*

GUAYMAS REGION 

The Guaymas region as defined here extends from 

the vicinity of Guaymas northward along the ooast nearly 

to Estero Tastiota. Gentry (19^9) referred to most of 

this region as the Guaymas Monadnook* It is largely vol 

canic in origin with much rhyolite and andesite and of 

very rugged relief* The shore from Bah£a San Carlos north 

to Estero Tastiota, a distanoe of nearly 80 kms., oonslsts 

of mountains and cliffs which reaoh direotly to the sea. 

It is a region of diffioult access and has been little col 

lected* The higher elevations are largely unexplored bio 

logically and promise to be very rewarding. 

Relatively reoent submergence has ocourred (Ander 

son, 1950; Shepard, 1950) and Anderson (1950, p. 7) states 

thati "The most obvious event in the Pleistocene or Recent 

history of the Guaymas area was the down-warping of the 

area adjacent to Guaymas which formed the harbor and indented 

the ooast line. 1 * The sea cliffs have deeply submerged ter- 

raoes which in the vicinity of Guaymas are at about 25 

fathoms (Shepard, 1950). Anderson (1950) provides a map 

and descriptions of the geology of the southern part of 

the Guaymas region. 

The environs of Guaymas and more reoently Bahfa 

San Carlos have been extensively altered by the encroach 

ments of oivilization; but still remarkably Intact and 

16

elatively original vegetation oan be found In olose proxi 

mity thereto* Host of the rest of the region, especially 

the coastal areas north of Bahfa San Carlos, remains In an 

essentially original and primeval condition. Encroachments 

of civilization due to the population pressure Is becoming 

Increasingly rapid and these regions are not expeoted to 

remain long unspoiled. 

Most of the vegetation of the Guaymas region con 

sists of relatively rich growths of mixed desert shrubs 

and small desert trees* Subtropical species are oommon 

and vegetation on the more favorable sites grades into 

thornsorub. The more arid sites9 however, support char 

acteristic xerophytic desert species* Esteros and quiet 

bays support rich growth of mangroves* Endemlo speoies 

are many but exploration is gradually extending the range 

of many of these supposed narrow endemlos* A number of 

other Guaymas endemics are now being recognized as syno 

nyms, yet the region is rich in distinctive forms (Shreve, 

1951). 

Two areas have been chosen for analysis in the 

Guaymas region: Bahfa San Carlos and Bahfa San Pedro, and 

discussions of these follow* - 

Bahfa San Carlos 

17 

The essentially natural communities in the vicinity 

of Bahfa San Carlos may be taken as representative of the

mountainous southern part of the Guaymas region. The 

original vegetation in the vioinlty of the city of Guaymas 

probably resembled closely that of the San Carlos area. 

Shore Zone.--In the quiet backwaters of Bah£a San 

Carlos dense and relatively extensive stands of mangroves / 

fill all but the tidal channels (today most of the man 

groves have been removed from the east end of the bay near 

the yaoht club). Bhlzoohora mangle Is especially abundant 

and generally outranks the other two species, Avloennla 

germlnans and Lagunoularla racemosa. Bhlzophora seems 

favored by the protection offered by the olosely set hills 

and mountains. A sharp contrast is produced between the 

verdant mangroves with their dense and evergreen foliage 

and the drought-deolduous desertscrub on the surrounding 

hills. At the east end of the bay rooky ledges, imme 

diately adjacent »o the mangroves in the bay margin, 

support desertscrub and giant columnar cacti (Paohyoerous 

prlnglel and Lemalreooereus thurberl). These ledges and 

slopes, often 2 to 3 meters above sea level, are commonly 

undercut and overhang the water? thus they allow for little 

or no lntergradation of vegetation and result in abrupt 

change, i.*e., a mosaic pattern. Where sea ledges are not 

present and the topography rises gradually, the mangroves 

give way to suoculent halophytes and salt grasses which in 

turn intergrade with desertscrub. Species occurring on

muddy and saline soils at Bah£a San Carlos between man* 

groves and desertscrub are sometimes flooded at high tide 

and include: 

Allenrolfea 

Ateiplex barclavana 

Bat Is mar* + Am* 

Mavtenus phvllanthoides 

Monanthochloe lUtPgftllg 

ptsiric* 

Seswrlum verrucosum 

s P9g9^9lV> 2ClESlBlfiM 

Suaeda torrevana 

Strand.—On the sandy-beach strands facing 

directly onto the sea or open bays, Bah£a Algadones 

and Bahfa San Francisco, there are low beach dunes and 

some much higher, shifting dunes. Characteristic species 

on the seaward-facing side of the strand include the 

following succulents and salt grasses: 

Abronia nmrltlfflfl 

AtrlPlra frftrclflYftP* 

flftllnnttiug nixsuE 

Jowea Pllosa 

Soorobolus 

These plants are subject to sea-spray and are buffeted by 

sea breezes and subsequently tend to be low and spreading. 

Occasional shrubs growing at the inland edge of the strand 

are wind-trimmed with their branches directed away from 

the ocean. 

19 

Occasional and very scattered small groves of palms 

(mostly Ervthea clara) occur along the inland edges of the 

broad and sandy beaches north of Bah£a San Carlos and

produce a landscape unique for the Sonoran ooast (Fig* 2). 

A single large SaTaal uresana has stood for several deoades 

or more on the upper beach near the yaoht club at Bah£a 

San Carlos and similarly occurring palms may have once 

been more common in the vioinity of Guaymas. A quadrat 

study was made in the above mentioned palm grove along 

the strand at the north side of Cerro Tetas de Cabra (Plot 

1, Table la Fig* 2). These palms ocour at the inner edge 

of the strand at approximately 20 meters from the high tide 

line* Along the strand Erythea is infrequent and the 

colonies highly localized* It reaohes maximum development 

in nearby rooky canyons and mountain slopes* Most of the 

other species listed in Table 1 are characteristic strand 

species* Jouvea pllosa* which occurs only along exposed 

beaches* reaohes maximum density at the seaward edge of 

the quadrat and does not range further inland* The 

remaining species all attain greater density and develop 

ment further inland* The two speoies of Bursera present 

do not reach maturity here and are waifs from desertsorub 

on the adjacent hills* Total plant ooverage is only 15% 

and aside from the palms which reach 7*8 m* in height the 

vegetation is less than 1 m. in height. Twenty species 

ocour in the quadrat and a total of twenty-one was found 

in the strand*

Figure 2. Upper strand, at base of northwest side of Cerro 

Tetas de Cabra. Erythea clara. Jatropha ouneata 

(left foreground), and Bebbia .lunoea (center 

foreground)•

TABLE 1 

PLOT 1. STRAND AT NORTHWEST SIDE OP CERRO TETAS DE CABRA, 

CA. 3 M. ELEV. SAND BEACH CA. 20 M. INLAND FROM HIGH TIDE 

TRUE. COVERAGE CA. 15%, C&LE GRAZING, 10 NOVEMBER 196^ 

Number Maximum Mean 

(500m 2 ) height height 

Speoles (ft) (ft) 

Erythea olara 25 25.5 22.8 

Bursera mlorophylla 21 2.7 1.8 

Phaulothamnus splnesoens - 2.1 - 

Bebbla junoea 5 2.0 1.8 

Lyolum sp. l 1.5 - 

Abutlion lncanum l 1.3 

Bursera hlndslana 3 l.l - 

Trills oalifornloa l 1.0 - 

Jatropha oinerea 2 0.75 - 

Passiflora arlda 1 0.75 - 

Antigonon leptopus 1 0.7 - 

Abutilon orispurn 1 0.5 - 

Phygrilanthus sonorensls JL - - 

Total *3 

Herbs Present: 

Amaranthus firabrlatus 

Amaranthus watsonll 

Boerhaavia of. erecta 

Coreocarpus sp. 

Dalea parryi 

Euphorbia pedioullfera 

Euphorbia setiloba 

Jouvea pilosa 

Total speoles in quadrat: 20 

Total speoles in stand: 21 

22

Plains.—Intermont or alluvial plains between 

Bahfa San Carlos and Guaymas are dissected by numerous 

dendritic dralnageways (Fig, 3) and locally may appear as 

an alternating series of flat-topped ridges and swales 

(Pig. Jf). The soils of the desert plain are generally 

coarse, relatively shallow, and with much small trans 

ported rook, while in the intervening swales or drainage- 

ways the soils are usually deeper and fine textured or 

powdery. The desert plain supports xerophytlc desertscrub 

while in the drainages and depressions there develops 

dense thornsorub resembling the coastal thorn forest of 

southwestern Sonora (see Gentry, 19^2). Two quadrat 

studies were made at a sample station located at oa. 5 

kms east of Bahia San Carlos, one on the desert plain 

(Plot 2, Table 2, Fig. 5) and the other in an adjacent 

swale (Plot 3» Table 3» Fig. 6). 

The more sparsely vegetated and light-oolored 

areas in the aerial photograph shown in Fig. 3 are desert- 

scrub. The south and west slopes of the desertscrub areas 

are clearly evident, although the slope gradients are very 

slight. On the ridge-plain shown in Fig. 5 (Plot 2) the 

major perennials consist of desert shrubs and cacti, of 

which the most numerous and conspiouous are Larrea 

divarloata and Jatropha ouneata. The tallest plant in the 

stand is Fouqulerla digue til (=«£• penlnsularls) whioh 

23

Figure 3* Aerial view of Sierra Naoapule; looking northward* 

Canon Naoapule is to the left and behind the lower 

ridge at left center. Note darker appearing upper 

bajada vegetation and thomsorub along drainage- 

ways. The relatively sparse desertscrub on south 

and west orianted non-dissected portions of the 

bajada appears light colored.

Figure 4. Effect of topography and soil on the olimax 

pattern of the vegetation at 5 kms. east of 

Bah{a San Carlos (Lat. 2?°$6* N.)» shown by 

dlagrammatlo representation of the disseoted 

alluvial plain with broad, mesa-like ridges 

supporting desertsorub bordering broad 

dralnageways supporting thornsorub (see text). 

The relative looatlons of Plots 2 (Table 2) 

and 3 (Table 3) are shown.

Meters 

rn~i 

GUAIACUM COULTERI 

PROSOPIS TORREYANA 

FORCHAMMERIA WATSONII 

PACHYCEREUS PECTIN-ABORIGINUM 

FOUQUIERIA DIGUETII 

LARREA OIVARICATA 

JATROPHA CMNEATA 

LEMAIREOCEREUS THURBERI

TABLE 2 

PLOT 2, ENSENADA SAN FRANCISCO, CA. $ KMS. BY ROAD EAST OF 

BAHIA SAN CARLOS AND CA. 1/2 KM. INLAND (NORTH) FROM SHORE, 

CA. 8 M. ELEV. MESA-ITKE RIDGE CREST. ROCKY SOIL, KITCHEN 

MIDDENS SCATTERED ON SURFACE. COVERAGE 35$. CATTLE GRAZING. 

12 JANUARY 1965 

Species 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Fouquieria diguetli 17 10.4 7.3 

Lemalreocereus thurberi 2 9.2 8.7 

Larrea divaricata 160 7.4 5.9 

Phaulothamnus spinescens 2 6.4 5.^ 

Jatropha cuneata 138 6.3 4.8 

Ceroidium microphyllum - 5.9 - 

Condalla lyoloides 3 5.8 5.7 

Jatropha olnerea 3 4.8 

Cordla parvlfolla 4 5.3 ».5 

Atamisquea emarglnata 2 5.2 - 

Citharexylum flabelllfollum 5 4.9 4.9 

Caesalpinia gracilis 9 ^.7 4.1 

Opuntla leptocaulis 8 *.5 2.9 

Maytenus phyllanthoides 2 *K3 ^.3 

Ruellia peninsularis 40 3.9 2.6 

Lophocereus schottii 1 3.7 - 

Opuntia versicolor - 3.7 - 

Lippia palmerl 1 3.5 - 

Simmondsla chlnensis 2 3.3 - 

Opuntia fulgida 37 2.8 2.2 

Krameria parvifolla 3 0.9 - 

Total 439 

26


Boerhaavla sp. 

Bouteloua arlstidoldes 

Ditaxis neomexloana 

Euphorbia polyoarpa 

Peotls palmerl 

TABLE 2—Continued 

Total speoles In quadrat: 24 

Total speoles In stand: 26

Figure 5* Desert plain or flat-topped ridge at ca. 5 kms» 

east of Bahfa San Carlos and oa. 1/2 km. Inland 

from shore. Jatropha ouneata and Larrea 

dlvarloata. Pole Is 5 feet.

TABLE 3 

PLOT 3- ENSENADA SAN FRANCISCO, CA. 5 KMS. BY ROAD EAST OF 

BAHIA SAN CARLOS AND CA. 1/2 KM. INLAND (NORTH) FROM SHORE, 

CA. 5 M. ELEV. SWALE, FINE TEXTURED AND DEEP SOIL. COVER 

AGE CA. 80$. CATTLE GRAZING. 12 JANUARY 1965 

Species 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Prosopis torreyana 6 20.8 17.7 

Pachycereus pectenaboriginum 

- 17.3 15.* 

Lemaireocereus thurberl - 14.2 - 

Forchammerla watsonii - 13.8 - 

Lyclum sp. 10 12.7 9.2 

Atamlsquea emarglnata 8 12.1 9.* 

0puntla leptocaulls 7 12.1 7.8 

Caesalplnla palmerl ll* 11.5 9.5 

Condalia lyololdes llf 11.3 8.9 

Sohoepfla shreveana - 11.1 - 

Maytenus phyllantholdes 7 10.2 8.2 

Gualacum coulterl «• 10.1 _ 8.8 

Matelea cordlfolla 1 10.1 - 

Phaulothamnus spinescene 26 9.7 8.9 

Randla thurberl - 9.7 - 

Lophocereus schottll 13 9.3 8.1 

Jatropha olnerea 26 9.2 7.0 

Cardlospermum corlndum k 8.8 - 

Cordla parvlfolia 70 8.7 7.0 

Lyclum sp. 5 8.7 - 

Mimosa laxlflora 3 8.4- 8.3 

Cltharexylum flabellifollum 5 7.^ 5.9 

Eohlnopterys eglandulosa - 6.7 4.6 

29

TABLE ^--Continued 

Lantana sp. 1 6.7 

Eupatorium saglttatum 10 6.6 

Haplopappus sonorlensis 48 6.5 5.7 

Prosopls artioulata 1 6*3 

Suaeda torreyana 11 6.3 

Condalla globosa - 6.0 5*7 

Bursera laxiflora - 5.8 

Ruellia peninsularis 28 5*3 4.0 

Jacobinia ovata 38 5*7 ^*8 

Abutlion inoanum 2 5*6 

Janusia califoraloa 7 5*6 

Berginia virgata 96 5*5 2.9 

Croton sonorae 21 5*^ ^*5 

Commlcarpus scandens - 5*3 

Janusia gracilis 2 4.8 

Maximo-wiczia sonorae 3 4.8 

0puntla versicolor 3 ^*1 

unidentified vine 3 

Hetastelma watsonianum 2 3*7 

Diclyptera resupinata 2 3«^ 

Opuntia fulgida 1 3«3 

Tragia amblyodonta 22 3*2 

Atriplex canescens 4 3*1 

Carlowrightia sp. 3 2.8 2.7 

Ferrooactus sp. - 2.7 

Jatropha ouneata 1 2.3 

Rathbunla alamosensis - 1.7 - 

Mammillaria cf. swingle! - 0.4 

Phoradendron callfornlcum 1 - 

Phoradendron diguetianum 1 - 

Struthanthus hankeanus 1 

Total 531 

30


Boorhaavla sp. 


Elytrarla lmbrlcata 


Ruellla nudlflora 

Setarla sp* 

Tidestromla lanuginosa 


Total species In quadrat: 48 

Total species in stand: 6l

Figure 6. Swale or dralnageways through desert plain at 

ca. 5 kms. east of Bah£a San Carlos and oa. 1/2 

km. inland from shore, Lyolum BP. (large shrubs), 

Prosopls torreyana. and large oolony of Phora- 

dendron oallfornloum (in Prosopls tree to left 

of pole). Pole is 5 feet.

attains 3*2 m.; however, the majority of the plant cover 

is about shoulder height. Approximately 35# of the surface 

here is covered by vegetation. A total of 26 species is 

enumerated in the stand and 2Ur of these occurred within 

the 0.1 hectare quadrat. The list of species shows that 

these are xerophytlo plants, largely with affinities to 

the desert regions to the north. With the exoeptlon of 

the two legume species# neither of which is common, the 

leaf-bearing plants here have small simple leaves, and many 

tend to be obovate to ovate shaped. Vlning plants are not 

present. Cattle grazing has eliminated Slmmondsla 

ohinensls from open areas and It survives only in the pro 

tection of large oolonles of spiny desert shrubs, e.g., 

Condalla lyololdes. It is possible that cattle grazing 

locally has also destroyed populations of other speoles. 

Plot 3 (Table 3i Fig. 6) was plaoed in the bottom 

of a swale ca. 50 m. west of Plot 2. Physiognomioally the 

vegetation compares with the thomsorub (= thorn forest, 

Gentry, 19*12) of southwestern Sonora. The vegetation here 

oannot be readily characterized by any one or several major 

perennials but rather by many speoles, each of which may be 

relatively common. Vegetation covers ca. 80# of the ground 

and before depredations by man and oattle it may have been 

even greater. A dense and thorny tangle of trees and 

undergrowth shrubs makes ingress difficult except by way of 

33

cattle trails which penetrate inuoh of the stand. The 

height of the nine tallest species measured at this stand 

exoeeds that of the tallest plant on the adjaoent ridge- 

flat (Plot 2), and trees and shrubs k m. and higher produce 

the majority of the total coverage. Forty-eight speoies 

were reoorded in the quadrat and 61 speoies in the stand, 

while additional species were quickly enoountered along the 

bottom of the swale away from the quadrat site. This is 

the greatest number of speoies per area yet reoorded in the 

Gulf Coast of Sonora. 

Speoies in the swale predominantly show affinities 

with regions of thornsorub to the south and several reach 

their northernmost limits in this vicinity. These include: 

Cltharexylum flabelllfolium 

Metestelma watsonlanum 

PltheooloBlum sonorae 

Schoepfla shreveana 

TlllandsTa exserta 

The occurrence of Tlllandsla exserta (Pig. 7) here repre 

sents the northernmost record for a non-parasitic epiphyte 

in western Sonora. Tlllandsla has not been found elsewhere 

in the Guaymas region and its narrow ecological range here 

indicates a critical difference in air moisture between the 

swale and the adjacent exposed ridge-flat. A wide array of 

growth-forms are common here, e.£., trees, columnar cacti, 

shrubs, vines, and epiphytes. Herbaceous perennials tend 

3^

Figure 7* Tlllandsla exserta. an epiphyte, growing on 

Gualaoum ooulterl in swale at oa. 5 kms. east 

of Bahfa San Carlos and oa. 1/2 km. inland 

from shore.

to be more numerous than the ephemerals, but neither are 

particularly well developed. 

Upper Ba.lada.—The upper bajadas are generally 

densely vegetated (Fig.3) with a mixture of thornsorub 

and desertsorub species. A quadrat study site (Plot 4, 

Table 4, Fig* 8) was looated in a representative area on 

the upper bajada at about 1 km* southeast of Canon Naoa- 

pule. Perennial cover amounts to about $0% although 

summer-fall ephemerals may seasonally carpet the ground 

with nearly 100$ cover. Many of the large shrubs and small 

trees tend to be well set apart from each other while 

smaller and seemingly shorter-lived and quioker-growing 

shrubs have aggregated patterns of distribution. The 

aggregated or olumped pattern seems at least in part to 

be the result of cattle grazing* The number of species is 

relatively high, i*e.» 44 speoies in the quadrat and 50 in 

the stand. The long list of species shows that the vegeta 

tion here cannot readily be characterized by any one or few 

species, although several species tend to be abundant or 

particularly conspicuous, e.*£*, Bursera mlorophylla, 

Fouauleria (both speoies), Colubrina glabra, and Ruellla 

penlnsularls. Only a few individuals of Bursera mloro 

phylla and Fouauleria are recorded in the quadrat; however, 

they are common here and the individual plants tend to be 

large and with broad crowns (Fig* 8). Several speoies of 

36

TABLE 4 

PLOT 4. CA. 1 KM. SOUTHEAST OF MOUTH OF CANON NACAPULE AND 

CA. 6 KMS. NORTHEAST OF BAHIA SAN CARLOS, CA. 60 M. ELEV. 

U?PER BAJADA. ROCKY-LOAM SOIL WITH MUCH GRAVEL AND SAND, 

COVERAGE CA. 50#. CATTLE GRAZING. 13 JANUARY 1965 

Maximum Mean 

Number height height 

Speoles (0.1 ha) (ft) (ft) 

Fouquierla maodougalil 1 12.7 - 


Fouquierla diguetii - 12.4 - 

Olneya tesota 1 11.3 10.3 

Hyptis emoryi 3 10.7 9.7 

Diphysa oooldentalls - 10.1 9.3 

Lemaireooereus thurberi - 9.7 - 

Colubrlna glabra 95 8.4 6.7 

Mimosa laxlflora 11 7.6 6.8 

Lyoium sp. 2 7.1 6.1 

3aplum blloculare 8 7.1 6.4 

Bursera laxlflora 5 7-0 6.3 


Ditaxis lanceolata 56 6.4 4.9 

Citharexylum flabelllfollum - 6.1 - 

Krameria sonorae 21 6.1 - 

Llppia palmerl 22 6.1 5.3 

Ruellla peninsularIs 100 5.9 4.2 

Meloohla tomentosa 6 5.7 4.3 

Randla thurberi 15 5.6 5.4 

Wllooxla striata 1 5.^ - 

Berglnla virgata 23 5.1 3.5 

Maxlmovlezia sonorae 1 5.1 - 

Cordla oylindrostaohya 2 5.0 - 

37

TABLE 4--Continued 

Janusla califoraloa 127 

Croton sonorae 27 

Nissolla sohottil 

Trills oallfomioa 9 

Carlowrightia sp. 4 

Jaoquemontla sp. 2 

Bebbia Juncea 

Tragla amblyodonta 5 

Janusla gracilis 88 

unidentified vine 2 

Krameria parvifolia 13 

Ayenla glabra 1 

Thryallls angustlfolia 9 

Abutlion crispurn 17 

Total 719 


Arlstlda adsoenslonls 



Cusouta sp. (parasite on Janusla) 

Dalea parryi 

Datura discolor 

Ditails neomezioana 

Euphorbia pedloulifera 

Phaseolus flliformis 

Setarla llebmannli 

Tephrosia sp. 

Tidestromia lanuginosa 

Total speoies in quadrats 44 

Total speoies in stand: 50 

4.9 

^•7 

4.6 

4.6 

4.1 

3.8 

3.9 

3.7 

3.6 

3.0 

1.9 

1.3 

1.3 

1.1 

3.2 

4.5 

2.3 

1.6 

38

Figure 8. Upper bajada oa. 1 km* southeast of Canon Naoa- 

pule. Ruellla pnnlnaularis (low shrubs)» Fou- 

aulerla maodougalll (center), and Bursera mloro- 

phvlla« Pole is 5 feet.

vines are present of which only Janusia is numerous* The 

assignment of individual plants into one or the other 

species of Janusia reported here is strictly provisional 

because of the partially defoliated state of the plants. 

Caoti are conspicuously rare and other succulents or 

aphyllous plants are absent* 

Mountains and Hills*'—Vegetation on rocky hills 

and mountain slopes in the vicinity of Bahla San Carlos 

and Guaymas may be characterized by spinescent and sarco- 

oaulescent shrubs and some small trees* On the more arid 

slopes suooulent plants including columnar caoti are well 

represented. Shallow-soiled rhyolite hills are generally 

sparsely vegetated but support diverse growth-forms, while 

deeper-soiled slopes tend to be more densely and uniformly 

vegetated. North and east-facing slopes very nearly approach 

thornsorub (subtropical scrub) in physiognomy and florlstio 

composition and hardly seem indicative of desert vegetation, 

while the more arid sites, i.*e,*» west and south-facing 

slopes, support characteristic desertscrub (Fig* 9)» in 

which the dominants are desert shrubs and oacti* 

Shallow-soiled hills and low mountains surrounding 

Bahfa San Carlos are largely of rhyolite. The soil pro 

files are very shallow and in some cases the bedrock is 

exposed and soil buildup is lacking. Vegetation cover 

varies greatly with exposure and development of soil but 

40

Figure 9* Aerial view of rhyolite hills between Bahfa San 

Carlos and Canon Naoapule; looking northward. 

Note dark-appearing thomsorub on east-faoing 

side of hills and lighter-colored desertsorub 

of mixed desert shrubs and small trees along 

alluvial plain or bajada.

msam

is generally sparse (Fig. 9). On slopes of exposed bed- 

rook the following character!atio rook-adapted species 

develop tenaoious holdfasts in crevices or cracks and 

crowd each other for space: 

Acacia wlllardlana 

Euphorbia oeroderma 

Flcus paTmerl 

Hoffmelsterla orasslfolla 

Lenalreocereus thurberi 

PerItvie palmerl 

Porphyllum pausodynum 

Flcus palmerl is often present but not common and here 

remains as a facultatively dwarfed shrub, although in nearby 

arroyos or canyons its roots may reach soil with sufficient 

moisture that it becomes a small tree. 

The summit at the south end of Punta Paradones was 

chosen as a site for a quadrat study on shallow-soiled 

rhyolite due to the essentially undisturbed nature of the 

stand (Plot 5» Table 5)* The most conspicuous species here 

include Acacia wlllardlana. Bursera mlorophylla. Fouquierla 

dlguetll. Jatropha cuneata and Lemalreooermus thurberi. all 

of whioh are widespread and common throughout the Guaymas 

region on similar sites. The major perennials are shrubs, 

medium to large in stature, and few individuals exceed 3 

meters in height. Average coverage is oa. but it is 

unevenly distributed, with coverage aggregated at slight 

depressions where there is some soil buildup and where 

runoff may produce slightly greater soil moisture. 

kz

TABLE 5 

PLOT 5« SOUTH END OF PUNTA PABADONES9 BAHIA SAN CARLOS, CA. 

30 M. ELEV. RHYOLITE BEDROCK, VERY LITTLE AND SHALLOW SOTE. 

CA. 3 TO 5 M. BELOW MESA RIDGE CREST, FACING BAY. SLOPE 15- 

17J6, COVERAGE CA. 35J*. 14 JANUARY 1965 

Species 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Aoaoia willardlana 16 11.8 10.2 

Fouquleria diguetli 60 9.6 6.6 

Lemalreocereus thurberl 2Ur 9.3 7.5 

Bursera mlorophylla- 96 6.9 5.3 

Dlphysa occidentalIs 1 6.4- - 

Desmanthus covlllel 9 5.9 if.9 

Marsdenia edulis 1 5.5 - 

Ferrocaotus sp. 1 5.1 3.6 

Jatropha ouneata 179 5.1 if.l 

Cltharexylum flab©111folium 2 - 

Bursera lailflora 1 it.O - 

Mimosa laxiflora 2 if.O - 

Croton sonorae 6l 3.8 3.^ 

Janusia graollls 7 3.6 - 

Kramerla sonorae 1 3.6 3.5 

unidentified vine - 3.5 - 


0puntla versicolor 19 3.0 - 

Agave yaqulana 1 3.0 mm 

Jacquemontla sp. 5 2.6 - 

Euphorbia tomentosa 30 2.5 2.3 

Abut 11 on califomicum 1 2.1 - 

Bebbia Junoea 1 2.1 - 

Cassia covesli 4 1.9 

Porophyllum pausodynum 1 1.8 - 

^3

TABLE Continued 

Agave sp. (sohottil-like) 2 1.6 

AbutIIon or1spurn 1 0.9 

Eohinooereus soopulorum 10 O.k 

Mammlllarla of. swingle1 53 0*3 

Mammlllarla Johnstonll 9 0*2 


Total 607 

Herbs Presentt 

Arlstida adscensionis 


Bouteloua arlstldoldes 

Cathestloum ereotum 


Euphorbia polycarpa 

unidentified forb (perennial) 

Total species in quadrat: 37 

Total species in stands 38 

244

Thirty-eight species are recorded in the stand and 37 

within the 0.1 ha* quadrat. Twenty-one peroent of the 

plants present (8 species) are succulents, i«e., cacti and 

agaves, and a number of the others may be classed as semi- 

suooulent, £•&•» Jatropha cuneata and Struthanthus 

hankeanus. Most of the species are small-leaved or 

aphyllous, with the single exception of Marsdenia edulls 

which is rare in this community. Truly ephemeral speoies 

are poorly represented and most of the herbaoeous oover 

oonsists of small perennials, e.g., Euphorbia polyoarpa 

and Cathestlcum ereotum. both of which are abundant here. 

At the north end of Bahfa San Carlos a dirt road 

leads through the bottom of a narrow valley and terminates 

at Bahfa Algadones. The oanyon floor supports riparian 

and semi-riparian growth with many subtropioal scrub ele 

ments represented by trees, palms, and a dense understory 

of shrubs. The natural vegetation has been seriously 

altered by extensive cattle grazing and woodcutting. The 

adjacent rooky slopes, however, are little disturbed and 

two stands (Plot 6, Table 6, Pig. 10; Plot 7» Table ?) 

were chosen for study and comparison at approximately 

1 km. north of Bahfa San Carlos, eaoh on the opposite 

side of the oanyon. 

Plot 6 (Table 6, Fig. 10) was located on a south 

west-facing slope on the east side of the oanyon. A rich

TABLE 6 

PLOT 6. CA. 1.2 KMS. NORTH OF BAHIA SAN CARLOS AT CA. 100 

M. BAST OF ROAD TO ALGADONES, CA. 25 M. ELEY. HILLSIDE CA. 

15 M. ABOVE VALLEY, EAST SIDE OF VALLEY. ROCKY SOIL. E3U 

POSURE SOUTHWEST, 245°» SLOPE 35#, COVERAGE CA. 60 


Maximum Mean 


Species (0.1 ha) (ft) (ft) 

Lemaireoeereus thurberi 55 13.1 11.7 

Diphysa oooidentalis 8 12.8 11.4 

Fouquieria diguetii 26 12.4 10.5 

Acacia willardiana 6 10.2 10.0 

Bursera microphylla 98 9-4 8.0 

Haematoxylon brasiletto 22 9.3 8.1 

Desmanthus covillel 213 8.8 7.3 

CrCton sonorae 86 8.1 7.1 

Manihot sp. 2 8.0 - 


Matelea cordifolia 6 7.8 - 

Coursetia glandulosa 1 7.6 - 

Mimosa laziflora 7 7-2 

Antigonon leptopus 39 7-0 - 

Ferrooactus sp. 7 6.5 5.8 

Randia thurberl 6 6.5 5.9 

Colubrina glabra 9 6.2 - 

Sapium bilooulare - 6.2 - 

Ayenia glabra 5 6.1 5.1 

Cardlospermum oorlndum 5 6.0 mm 

Opuntia versicolor 23 5.7 4.7 

Melochia tomentosa 46 5.4 4.7 

Nlssolia schottii 12 4.9 - 

Euphorbia oeroderma 6 4.7 3.6 

46

TABLE 6—-Continued 

Bursera laxlflora 26 *J-*6 3*8 

Berglnia vlrgata 12 4*5 3*7 

Trixis californloa 11 3.9 

Opuntia gosslllniata 2 3*7 

Janusia graoilis 132 3*6 3*1 

Kramerla sonorae 1 3.5 

Cordla parvlfolia 1 3,4 

Agave yaqulana 21 3.2 

Rue11la penlnsularls 40 3*2 3*0 

Lippia palmerl - 3«1 

Abutlion lnoanum 1 2.9 

Maximowlozia sonorae 30 2,8 

Hechtla montana 537 l* 1 

Hammillaria sp. 12 0*3 

Mammlllaria Johnstonil ^ 0.3 

Phygrilanthus sonorensis 4 


Total 1731 


Commelina sp* 


Euphorbia pedlcullfera 

Euphorbia setlloba 

Ipomoea sp. (vine, annual) 

Panioum arlzonicum 

Physails sp. 

Setaria sp* (liebmannil) 

Tephrosia sp* 


unidentified Grammeae (annual) 

unidentified Grammeae (perennial) 


Total species in stand: 53 

**7

Figure 10. Southwest-facing slope ca. 1.2 kms. north of 

Bahfa San Carlos. Lemalreooereus thurberl. 

Aoaola Klllardlana. Jatropha ouneata (oenter), 

Saplum bllooulare (In front of large Lemalreo 

oereus . left oenter), and Ruellla peninsular1b.

TABLE 7 

PLOT 7- CA. 1 KM. NORTH OP BAHIA SAN CARLOS AT CA. 1/4 

KM. WEST OP ROAD TO ALGADONES, CA. JO M. ELEV. HILLSIDE 

AT FOOT OP ESCARPMENT AND CA. Z5~M. ABOVE VALLEY, WEST 

SIDE OP VALLEY. DEEP ROCKY~SOIL. EXPOSURE EAST, 90°. 

SLOPE 32#. COVERAGE 100#. SLIGHT CATTLE GRAZING. 14 

JANUARY 1965 

Species 

Number 

(250m2) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Forohammerla watsonil 1 18 

Bumella occidentalis 17 17 13.3 

Bursera miorophylla 14 - 

Colubrina glabra 11 14 - 

Guaiaoum ooulteri 4 14 - 

Cordla sonorae 27 13 10.0 

Bursera laxlflora 1 12 - 

Antigonon leptopus 18 10 - 

Coursetla glandulosa 1 10 - 

Jaoqulnia pungens 1 10 - 

Lysiloma divarloata - 10 - 

Sapium bilooulare 3 10 - 

Lycium sp. 4 9 - 

Phaulothamnus spinesoens 2 9 - 

Matelea cordifolla 2 8 

Cardiospermum corindum 6 8 - 

Ditaxis lanoeolata - 8 6.3 

Ipomoea sp. (vine) 1 8 - 

Krameria sonorae 6 8 - 

Fouquierla diguetii - 7.5 - 

Jacobinia ovata 27 7.3 5.9 

Berginia vlrgata 2 7 5.8 

Lippia palmerl 2 7 6.0 

49


Randla thurberi 1 7 - 

Ruellla peninsularIs 121 6*3 5*^ 

Nlssolla schottll 5 6 - 

Croton sonorae 15 5 

Janusla graollis l 5 

Maytenus phyllantholdes 1 5 

Maxlmowlozla sonorae 1 

unidentified vine 2 b 

Haplophyton clmioldlum 21 2.9 

Masoagnla maeroptera 2 3 - 

Tragla amblyodonta 28 3 

Total 33*+ 


Abut11on orispum 

Amaranthus watsonii 

Euphorbia pedloullfera 

Tephrosla sp. 


unidentified Gramlneae (annual) 


Total speoies in quadrat: 37 

Total speoies in stand: Jfl 

50

growth of sarcocaulescent desertscrub produces approxi 

mately 60fi ground cover. Fifty-one species were found in 

the quadrat and an additional two species were found nearly 

adjaoent thereto. Growth-forms include stem and leaf suo- 

oulents, vines, epiphytic parasites, various perennial and 

ephemeral herbs, and a preponderance of shrubs, many of 

which are sarcooaulesoent, spinescent, and drought- 

deciduous. Trees are generally lacking although the dis 

tinction here between large shrubs and small trees is 

subjective, with maximum orown height scarcely exceeding 

m. The non-suoculent plants are all drought-deciduous 

and those with compound leaves (£•£•, Bursera and Leguml- 

nosae) or highly divided leaves (e,»£»t Manlhot. Maxlmo- 

wlozla. and Cardlospermum) appear to be as common as those 

with simple leaves. Among the most conspicuous and abundant 

species here are: 

Bursera mlcrophylla 

Desmanthus oovlllel 

Fouaulerla dlguetll 

Hechtla montana 

Janusla gracilis 

Jatropha cuneata 

Lemaireocereus thurberl 

Hechtla reaches Its maximum population density here. A 

dozen species of herbaceous plants are present and at least 

half of these are ephemerals. The relatively rich growth 

on an otherwise harsh habitat (lê., a southwest exposure) 

seems to be due, at least In part, to the site being 

51

sheltered from wind and its proximity to the sea would 

I 

aooount for a relatively high humidity. 

Plot 7 (Table 7) was located on a northeast slope 

on the opposite side of the oanyon from Plot 6. The 

exposure is east and slightly north. The topography of 

the two sites appears essentially similar and difference 

in exposure seems to be the most marked habitat variable. 

The vegetation consists largely of thomscrub species which 

form a low and spiny tangle of small trees and large shrubs. 

Similar appearing vegetation is shown in an aerial photo 

graph (Fig. 9) taken several kilometers east of Plot 7* 

Coverage is 100^ with orown heights of 4 to 6 m. Caotl 

and other succulents are wholly lacking and the plants 

present are not saroocaulescent. In comparison with other 

habitats the vegetation presents a particularly leafy 

aspect and vines are prevalent and often quite large. 

Bursera mlorophylla and Fouqulerla diguetil* although very 

common at Plot 6, are rare here. Species with simple as 

well as compound and highly divided leaves are well repre 

sented. Most of the species are drought-deciduous 

although several evergreen or semi-evergreen species are 

present) £..£,•» Forohammerla watsonll. Jktnulnla pungens 

and Mavtenus Phyllantholdes. Forty-one species are enu 

merated from the stand; however, due to extenuating cir 

cumstances the site was not adequately searched for 

additional species. 

52

Riparian Canyons.--Deep and narrow gorges or can 

yons in the Guaymas Monadnook between Bahfa San Carlos and 

Bahfa San Pedro support rloh and verdant riparian 1 growth 

of a subtropioal nature. Canon Naoapule (Fig* 11) was 

ohosen as a representative riparian canyon habitat (Plot 8, 

Table 8). The oanyon lies ca. 5 kms. northeast of Bahfa 

San Carlos at the base of the mountains and is aooesslble 

by a secondary dirt road* The name naoapule refers to the 

large native fig, Flcus padulfolla* whloh yields a small 

edible fruit* The oanyon walls are high, nearly vertical, 

and provide shade for much of the canyon* The lower part 

of the oanyon runs east and west while the upper oanyon 

turns and is oriented north and south* A stream flows 

the year round in the upper part of the canyon and inter 

mittently through the remaining portion* Cattle grazlngt 

wanton burnings and woodcutting in the past several years 

have substantially obliterated the original beauty of the 

oanyon. The upper part with groves of palms and Flous 

trees is the most seriously altered, due in part to the 

presence of permanent water whloh attracts man and beast 

alike* Yet reoovery for at least some of the plants is 

rapid and parts of the oanyon remain in a substantially 

original condition* 

1* See Lowe (196*0 for a definition and discussion 

of riparian communities in the Sonoran Desert*

Figure 11. Canon Naoapule, looking west towards entrance 

of canyon* Grassy area in foreground has been 

cleared of shrub cover•

TABLE 8 

PLOT 8* CANON NACAPULE. CANYON BOTTOM AT CA. 1/2 KM. WEST 

OP MOUTH OF CANYON, CA. 130 M. ELEV. GRAVEL AND SAND SOIL, 

DEEP, AND WITH MUCH HUMUS AND BOCK. CATTLE GRAZING. COVER 

AGE CA. 98£. 13 JANUARY 1965 

Species 

Number 

(250jb2) 

Maximum 

height 


Marsdenla edulls 2 9.0 7.9 

Randla sp 2 9.0 8.1 

Cardlospermum oorlndum 3 7.3 - 

Coooulus dlverslfollus - 7.1 - 

Randla thurberl 1 6.*t - 

Calllandra rosel 8 6.3 5.5 

Maxlmowlczla sonorae 1 6.2 - 

Mimosa laxlflora mm 6.2 

Pranserla ambrosloldes - 9 - 

Acalypha califomloa 2 **•? *.5 

Jaooblnla ovata 16 k.6 3.8 

Trlxls oallfornloa - - 

Brlokellla sp. 20 i*.l 3.6 

Dltaxis laneeolata - *K1 - 

Bursera laxlflora 2 *K0 - 

Dodonaea vlscosa - J*.o - 

Benthamantha edwardsil 5 3.9 - 

Tragla amblyodonta 1 3.2 - 

Franserla oordlfolla - 3.1 - 

Vaseyanthus InsularIs - 2.8 - 

Abutllon lnoanum 1 2.2 - 

Mascagnla maoroptera - 1.3 - 

Elytrarla lmbrlcata 2 1.1 - 

Hofmelsterla crassifolia - 1.0 - 

Plumbago scandens 1 0.5 - 

Total 168 

Herbs Presents 


Perltyle palmerl 

56

TABLE 8—•Continued 

Perltyle oalifomloa 

unidentified Cruoiferae 

unidentified forb (perennial) 

Total speoies in quadrats 4l 

Total species in stands 55

In contrast to the canyon floor the walls of the 

canyon are partially barren. Palms (Ervthea clara) grow 

out of the rooky, often sheer cliffs and mountain slopes 

above the canyon floor, lending an unusual aspect to the 

landscape* Other common rock-adapted species clinging to 

the cliffs Include Asplenias leptopus. Agave ohrysoglossa. 

Pious petlolarls. Hofmelsterla crassifolla and Perltyle 

palmerl. On the slopes of more gentle gradients with a 

soil profile there are dense stands of shrubby scrub which 

quickly grade into the arborescent riparian vegetation 

along the canyon floor* Vegetation on north and east- 

facing slopes is relatively verdant and resembles, to a 

greater or lesser degree—depending upon steepness of 

slope, that of Plot 7; while the more arid south and west- 

facing exposures tend to resemble Plots 5 and 6. 

Along the canyon floor large shrubs and small 

trees produce a closed oanopy with crown heights generally 

ranging from 4 to 6 m« The vegetation is weakly strati 

fied into tree, shrub, and ground herb layers and are 

interlaced by vines and soandent shrubs. 

The majority of coverage here is produced by large 

spreading shrubs, £•£•, Coocoloba goldmanll. Coursetla 

glandulosa, and Vallesla balleyana. Vlning plants are 

abundant, better developed than anywhere else In the Gulf 

Coast of Sonora, and include 10 species. The most abundant 

58

and rank-growing vines here are Antigonon leptopus. Gouanla 

rosei, and Passiflora mexloana. These vines often envelop 

and cover trees and shrubs. Ephemerals are of only minor 

consequenoe and other herbaceous plants are also poorly 

developed. 

Fifty-five species are recorded at the quadrat 

site and 41 of these occurred within the quadrat. The 

quadrat was 5 * 50 m. in size rather than the standard 

20 x 50 m. (0.1 ha.) due to the demands of the topography 

and condition and extent of natural areas of vegetation. 

Thus a greater number of species might be expected in a 

quadrat of 0.1 ha. in size. 

The vegetation of the canyon floor is noticeably 

verdant and arborescent. Due to the perennial souroe of 

soil moisture and equable air temperature and moisture* 

the foliage is to a large extent evergreen. Interestingly* 

there are no aphyllous or succulent species in the quadrat 

study area. Succulents are rare along the canyon floor 

and are limited largely to crevices among solid rock and 

reach greater development on the adjacent canyon walls, 

e.j£., Asoleplas leptopus and Hofmelsterla crasslfolla. 

A large number of the oanyon floor species have glabrous 

or only sparsely pubesoent leaves as compared with related 

taxa and/or populations in more arid habitats; £•£•» 

Passiflora mexlcana. found nowhere else in the Gulf Coast 

59

of Sonora, has glabrous leaves while P. arlda and P. 

foetlda whioh are more widely distributed are densely 

pubescent. Leaves of Flous petlolarls growing in shady 

and well-watered parts of the oanyon are nearly glabrous 

(exoept for the characteristic patch of fuzz, "tomentose 

tuft," at the base of the lower side of the leaf blade) 

and intergrades into more densely pubesoent forms growing 

on the more arid reaohes of the adjacent slopes, thus 

vitiating one of the major differences between F. petlo 

larls and F. palmerl. A particularly interesting case 

occurs with Zanthoxvlum arborescene, whloh is otherwise 

known only from southern Baja California and Slnaloa 

(Wiggins, 1964-). The Naoapule population is glabrous, 

although in Baja California and Slnaloa it characteristic 

ally has tomentose leaflets, at least on the undersurface 

(Hose, 1897; Standley, 1923; Wiggins, 196*0. Whether or 

not the Sonoran population represents a genetic or environ 

mental variation is an intriguing question whloh can only 

be ascertained with additional speoimens or in a standard 

garden. The eoologio distribution of the three species 

of palms is particularly elucidating with relation to 

their leaf investure. Washlngtonia robusta with shiny 

green and relatively thin glabrous leaves occurs only 

along the immediate margins of the stream. Its range is 

limited to the portion of the stream with permanent water

where It locally outnumbers other palms. 3abal ureaana 

has a muoh tougher leaf, conspicuously glaucous but other 

wise glabrous. It oocurs along the oanyon floor into 

areas of only temporary water and similarly occurs else 

where in the San Carlos region along arroyos without 

permanent water. Ervthea olara is the most widespread 

and drought-tolerant palm in the Gulf Coast of Sonora and 

it is abundant on arid rock slopes and cliffs, canyons, 

and occasionally even on the beaoh (Table 1, Fig. 2). 

Corresponding with its broader environmental distribution 

is a tough glaucous leaf with very dense silvery-lepidote 

pubescenoe. 

Arborescent species along the canyon floor are 

generally scattered in small groups of several adult indi 

viduals or singly and the riparian vegetation cannot be 

characterized by any one or several elements. For this 

reason and beoause of the large size of major perennials 

it is thought that the single quadrat is highly inadequate 

for sampling or representing the wealth of arborescent 

species ooourring here. Additional species are quickly 

encountered as one walks through the canyon floor. The 

rich and subtropical nature of the vegetation is shown 

by the following list of speoies found along the floor 

of Canon Naoapulei

Abutlion lnoanum 

Aoaola wlllardlana 

Acalypha oallfornlca 

AmarantTTua wataonll 

Antlgonon leptopus 

Arlstlda*"BP. 

Beloperone oallfornlca 

Bentnamantha edwardsll 

Bouteloua arlstldoldea 

Buaella""oooldentalls 

Bursera laxlflora 

Calllan'dra rosaT*" 

Cardloapermum corlndum 

Celtls reticulata 

Celtls pallida """" 

Cooooloba goldmanll 

Coooulus*"llveralf ollus 

Coamlcarpus soandens ~ 

Condalla BP. 

Cordla sonorae 

Coursetla glandulosa 

c ou tar ea""*latl folia 

Datura "cTlsoolor 

D1 taxis lanoeofata 

Dodonaea vlscosa 

Eleooharls genfculata 

Slytrarla lmbrlcata 

Ervthea olara 



Pious petiolarls 

Flous padulfolia 

Floua radullna 

Franserla ambr'osloldes 

Franserla oordlfolla 

Fulrena simplex 

Guaanla rosel 

Guaiaoum ooulterl 

Haematoxylon braslletto 

Hermannla pauolflora "" 

Hofmelaterla oraaalfolla 

Hofmelaterla laphamloldes 

Jaoaulnla pungena 

Lagasoea deolPlena 

Lyslloma dlvarlcaEa 

KarsdenlTa edulls 

Maaoagnla maoroptera 

Maxlmowlczla sonorae 

Nlaaolla aohottll 

Pasalflora mexloana 

PerltTie oallfornlca 

Perltyle palmerl 

Phaulothamnus splnesoens 

Physalls BP. 

Plumbago soandens 

Porophyllum pausodypum 

Handla thurberl 

Band la ap. 

Sabal uresana 

Saplndus aaponarla 

Saplum Tllooulare 

Tragla ambylodonta 

Trlxla oallfornlca 

Vaseyanthus InsularIs 

Valleala balleyana 

Washington!a robusta 

Zanthoxylum arboresoens 

Zanthoxylum aonorenae 

unidentified Compoaltae 

unidentified Cruel ferae 

unidentified forb 

The tallest trees in the canyon are Vlashlngtonla robusta 

which attain a height of approximately 20 m. and Flcus 

radullna which reaches ca. 15 m. in height. This fig has 

small but prominent buttressed roots and as such is unique 

in the Gulf Coast. 

62

Bahfa San Pedro 

63 

Bahfa San Pedro ("Ensenada Grande) lies about 20 km, 

northward from Bahfa San Carlos and oross-ohannel from Xsla 

San Pedro Nolasco. Its vegetation is relatively rioh and 

due to a oomplex topography it is highly varied. Environ 

mental conditions here are ameliorated by marine influence, 

protection from desert winds by closely set mountains, and 

locally greater souroes of moisture gained from mountain 

runoff and orographic precipitation* 

At the north and south ends of the nearly semi- 

oiroular bay are high and rocky headlands with palms 

(Erythea olara) growing on their seacliffs« Beaoh dunes 

border most of the east shore of the bay and a bajada not 

more than 1 or 2 kms. in width oooupies most of the area 

between the dunes and the mountains. A narrow playa with 

a north-south axis lies inland a short dlstanoe from the 

coastal dunes. The mountains behind the bay rise abruptly 

into the biologically unexplored highlands of the Guaymas 

Monadnook. An aerial view of the bay (Fig. 12) suggests 

an extinot and partially submerged crater open to the sea 

at its west side. 

Vegetatlonal gradients at Bahfa San Pedro and 

Bahfa San Carlos show close resemblance} however, the 

vegetation at San Pedro appears slightly less xerophytic. 

Inland from the bay the mountains rise steeply and qulokly.

Figure 12. Aerial view of Bahfa San Pedroj looking south 

ward. Note playa In upper center of picture.

. J s ->-t -(A 

64

The higher elevations southward and Inland to about the 

vicinity of Canon Naoapule are oovered by a low, thin 

forest of small subtropical scrub trees and shrubs In 

which Lyslloma dlvarloata is prominent (Fig* 13)* Close 

aerial inspeotlon of this region and the higher elevations 

of Sierra Kunkaak on Isla Tiburon reveals thornscrub whloh 

in gross physiognomy is not unlike the areas of eootone 

between thorn forest and short-tree forest (Gentry, 19^2) 

in southeastern Sonora. 

A relatively rapid transition into a somewhat more 

zerophytic vegetation ooours within several kilometers 

north of Bah£a San Pedro. The northernmost limit of a 

number of species occurs at or near Bahfa San Pedro but 

few if any plants of northern affinity reach their southern 

limits here. Conspicuous among the plants not found along 

the coast north of the vicinity of San Pedro (or several 

kilometers thereof) are: 

Agave sp. (large Euagave) Gossyplum klotzohlanum 

EeStKamantha edwardsll Hechtla montana 

Coocoloba goldmanl1 Hofmelsterla orassifolia 

Cordla sonorae Indlgofere. laevls 

Dlphysa occidentalis Lyslloma Candida 

Erytnea olara Mamallla'rla .lohnstonll 

Euphorbia ceroderma 

Trfyig

of Baja California, is known extralimitally only from the 

vicinity of Bahfa San Pedro. Croton magdalenae shows a 

similar distributional pattern but it also occurs on Isla 

Tiburon.

Figure 13• Thornscrub near Pico de Guaymas, between Canon 

Hacapule and Bahfa San Pedro, oa. 500 to 700 m. 

elevation.

'•M 

1 

66

Playa,—The simplest communities at Bah£a San 

Pedro are along the beach and at the small playa Just 

Inland from the center of the bay. 

The playa Is roughly 3/4 km. long and la unique for 

the coast of the Guaymas region (Figs. 12 and 15)* Allen 

rolfea oocldentalls covers much of the area but the oenter 

and lowest part of the playa Is devoid of vegetation. 

Peripheral to the Allenrolfea Is a large and well estab 

lished stand of Phragmltes communis. Strangely the olose 

association of Allenrolfea and Phraamltes Is not repeated 

elsewhere In the Gulf Coast of Sonora. Phragmltea Is 

characteristic of tlnajas or waterholes In Sonora but In 

the Guaymas Honadnook It has been found only at this 

locality. 

Shore.—Sandy beaches along the shore of the bay 

are characterized by simple communities of harsh-leaved 

and perennial salt grasses and several sand-adapted halo- 

phytes. Two quadrats were made on the windward side of 

the low dune near the south end of the bay (Fig. 14)* 

one extending Inland 10 m. from the high tide zone (Plot 

9, Table 9) and the other Immediately adjacent to and 

Inland from the latter (Plot 10, Table 10. In Plot 9 

total plant ooverage amounts to only oa. Z% with 6 species 

of plants present. Plot 10 shows a slight lnorease with 

7 species and a total coverage of ca. Snorobolus 

67

Figure 1^« Windward side of beaoh dunes at Bah£a San Pedro* 

Sporobolus vlrpclnlous (lower baaoh) and Jouvea 

pllosa (upper beaoh).

TABLE 9 

PLOT 9* BAHIA SAN PEDRO, BEACH AT CENTER OF BAY, CA. 0-1.5 

M. ELEV. ABOVE HIGH TIDE LINE. WEST EXPOSURE, SLOÊ CA. 5%. 

BEACH SAND. COVERAGE CA. 2%, 11 NOVEMBER 196Jf 

Species 

Number 

(500m2) 

Nazlmum 

height 

(ft) 

Mean 

height 

(ft) 

Bebbla Junoea 3 1.6 — 

Jouvea pllosa 17 l.*f 1.3 

Atrlplex barolayana 5 1.2 - 

Sporobolus vlrglnlous 83 1.0 0.9 

Croton oallfomloa 5 0.9 0.7 

Enoelia farlnosa (dead) 2 - - 

Total 115 

Total species In quadrats 6 

Total speoles In stands 6 

69

TABLE 10 

PLOT 10. BAHIA SAN PEDRO, WINDWARD SLOPE OF BEACH DUNE AT 

CENTER OF BAY, CA. 1.5-2.5 M. ELEV. ABOVE HIGH TIDE LINE. 

WEST EXPOSURE, SLOPE CA. 15-20#. BEACH SAND. COVERAGE CA. 

^Tl NOVEMBER 1965 

Maximum Mean 


Speoies (500m 2 ) (ft) (ft) 

Bebbla Junoea 

0puntla fulglda 

Croton oallfornloa 

Jouvea pllosa 

Total 

Herbs Present; 

Amaranthus flmbriatus 


Palafoxla linearis 

Total speoies In quadrats 7 

Total speoies In stands 7 

8 1.9 1.5 

2 1.6 

58 1.3 0.7 

82 1.3 1.2 

1*5 

70

vlrglnloua Is widespread on the lower beaoh, and below 

Plot 9 it actually grows Into the upper limits of the high 

tide zone. On slightly higher terrain, but still on the 

windward side of the dune, Sporobolus is gradually replaced 

by Jouvea pllosa and a few perennial forbs, e.g., Croton 

californlcus. Jouvea extends onto the dune crest but 

quickly drops out on the lee side. Forbs present on the 

windward sides all reach greater oonoentration on the lee 

sides of the dunes (Plot 11, Table 11). Ephemerals, with 

rare exception, are absent from the lower beaoh in the 

region of Sporobolus (Plot 9) and are first encountered 

on the upper beaoh, becoming oommoner on the lee side of 

the dune. Euphorbia polvcarpa is the only oommon ephemeral 

on the windward slope of the dunes. 

71 

Proceeding from the windward to the lee side of the 

dunes, salt grass quickly gives way to a more complex 

desertsorub with dune-adapted small desert shrubs (Plot 11, 

Table 11, Pig. 15)* Jouvea is abundant along the crest of 

the dune at the west margin of the plot but does not extend 

inland more than 10 m. from the dune crest. Host of the 

species recorded here are widespread and characteristic of 

dunes along the coast of Sonora. Nineteen speoles were 

found in the quadrat and 21 in the stand, and about 30$ 

of the ground surface is covered by the vegetation. Some 

of the desert shrubs are here poorly developed and dwarfed

TABLE 11 

PLOT 11. BAHIA SAN PEDRO, CREST AND LEE SIDE OF BEACH DUNE 

AT CENTER OF BAY, CA. 3*5-5 M. ELEV. ABOVE HIGH TIDE LINE. 

BEACH SAND. AVERAGE CA. 33#. H NOVEMBER 1965 

Maximum Mean 


Speeiea (0.1 ha) (ft) (ft) 

Vlsoalnoa genioulata 7 6.1* 

Antigonon leptOpus - 6.4 

Jatropha ouneata 63 5*2 4.4 

Jaoquinia pungens 2 5«2 

Colubrina glabra 8 5*1 

Lyoium sp. 1 4.5 

Enoella farinosa 23 3*3 2.8 

Guaiaoum coulter1 2 2.9 2.1 

Trixls californloa 3 2.7 

Bursera miorophylla 4 2.6 

Bebbia junoea 118 2.3 1.7 

Bourreria sonorae 1 2.3 

Maytonus phyllanthoides 1 1.9 

Jouvea pllosa 268 1.5 1*0 

Croton californioa 130 0*9 0.7 

Lyrooarpa coulteri - 0.8 - 

Forohammeria watsonii 1 .7 

Phoradendron diguetianum 1 

Total 633 


Amaranthus fimbriatus 


Palafoxia linearis 



72

Figure 15* Crest of low beach dune, Bahfa San Pedro] look 

ing east* Bebbla junoea. Croton oalifornious. 

Jatropha ouneata, and Jouvea plloaa in foreground* 

Part of playa with Phragmltea communis in middle*

as compared with those of neighboring inland areas, e.g>, 

Bursera nlorophylla. Gualaoum coulterl. Forohammerla 

watsonll and Jaoqulnla pungens• 

Bajada.—BaJadas and pediments with ooarse, deep 

soils support relatively dense stands of mixed desert shrubs 

(Fig* 16)• Perennial ooverage is often 50# although the 

range is from approximately 35 to 75%* Summer-fall 

ephemerala may produce nearly 100/6 coverage but winter- 

spring growth is muoh more weakly developed, at least in 

some years. Succulent plants are generally absent or rare* 

Common species on the bajadas at Bahla San Pedro include: 


Andraohne clllatof 

laricTulosa 

gonon leptopus 

Antirrhinum oyathlferum 

Atamlsauea emaralnata "" 

Atriplex linearis 

Bursera"""hlndslana 

Bursera mlcrophyTla 

Caesalplnia gracilis 

Cardlospermum oorlndum 

Cassia oovesll 

Colubrlna glabra 

Condalla""nclobosa 

Condalla lycloldes 

Cordla piarvifolla 

Groton sonorae 

Pitaxis lanoeolata 

Enoella farlnosa 




Ferrooactus sp. 

Fououlerla diguetil 

Hibiscus denudatus 

hibiscus sp. 

JaoQuemontla 3p. 

Janusla oallfomlca 


Jatropha ouneata 

Kramerla sonorae 

Lemalreocereus thurberl 

Lyclum SP. 

Lvrocarpa ooulteri 

Manual liar la sp. 

Olneva teaota 

Qpunila fulglda 

Qpuntla versicolor 

Perltvle oallfomlca 

Perltyle enoryl 

Phaulothamnus splnescens 

prosopls torreyana 

Randla obcordata 

Buellla peninsularIs 

^mmnnrta\a ohlneUSlS 

Tldestromla lanuginosa 

Trlxls californlous 

Vlscalnoa genlculata 

South Slopes• -South-facing slopes are generally 

vegetated with mixed desert shrubs and some columnar oacti 

7^

Figure 16. Early fall aspect of upper bajada at Bahfa Sau 

Pedro. Bursera mlorophylla. Jatropha ouneata, 

0puntla versicolor, and Tidestromia lanuginosa.

(Plot 12, Table 12v Fig. 1?). The soil is rooky, coarse, 

and of moderate depth. Coverage is greatest at the base 

of hills or upper bajadas and gradually thins onto higher 

slopes with shallower soils. At the quadrat site (oenter 

of photograph, Fig. 1?) oa. $0% of the surfaoe is oovered 

by perennial growth. Forty speoies were found in the stand 

and 37 within the quadrat. The oommon desert shrubs here, 

e.£*» Cordla parvlfolla. Bnoella farlnoaa. Jatropha ouneata, 

and Ruellia peninsular is have small and simple leaves. 

Rooky cliff8 and steep slopes of nearly solid rook 

support large columnar oaotl, e .£., Carneglea glgantea, 

Lemalreooereus thurberl« and Paohyoereus prlnglel. and 

several nearly arboresoent desert shrubs, e.g.. Aoaoia 

wlllardlana and FouQulerla dlguetll (Fig. 17). These plants 

have their roots anchored in rock crevices. 

Pediment.—-A low rocky pediment extends north from 

the hills at the north end of Bahfa San Pedro. It consists 

largely of exposed rhyollte bedrock and supports thorny 

desertscrub (Plot 13, Table 13)* Plants are concentrated 

along fractures where the roots can penetrate the rook and 

along shallow drainageway depressions in which a thin 

and rooky soil profile is present. Average coverage is 

oa. 35^ although the plants tend to be aggregated and 

unevenly spaced. A total of 36 speoies was found within 

the 0.1 ha. quadrat and an additional 15 speoies were 

76

TABLE 12 

PLOT 12. BAHIA SAN PEDRO, CA. 1/2 KM. INLAND (NORTHEAST) 

FROM SHORE AT NORTH END OF BAY, CA. 12-15 M. ELEV. ROCKY 

HILL, VOLCANIC ROCK AND SHALLOW SOIL. SOUTH EXPOSURE 170* 

175°» SLOPE **6£. COVERAGE CA. 50%• 19 JANUARY 1965 

Maximum Mean 



Carneglea glgantea - 19 - 


Lemalreocereus thurberl 3 9.** - 

Bursera mlorophylla 23 8.1 - 

Jatropha ouneata 75 6.7 5.2 

Cordla parvlfolia 171 6.6 5.8 

Ceroidlun mlorophyllum - 6.^ - 

Colubrina glabra 11 5*5 *.9 

Jaequemontla sp. 3 5»b - 

Desmanthus oovlllel 13 5-3 ^.3 

Janusla gracilis 29 *t.8 - 

Slmmondsla ohlnensls 2 8 - 

Huellla peninsularIs 90 **•7 2.9 

Phaulothamnus spinescens - Jf.l - 

Opuntia versicolor 1 3.9 - 

Dltaxis lanoeolata 1 3.8 mm 

Enoelia farlnosa 102 3.7 3.^ 

Abutllon lnoanum 2 3.6 - 

Kramerla sonorae 2 3.6 - 

Croton sonorae 6 3.3 - 

Llppla palmer1 5 3.3 - 

Hibiscus denudatus 30 2.9 2.3 

Melochia tomentosa 3 2.7 - 

Passiflora sp. 1 2.5 - 

77


Perrooaotus sp. 1 2#3 

Abutllon or1spurn 5 1*2 

Mammillarla sp* 1 0*3 

Total 585 


Allionia lnoamata 

Amaranthus watsonli 


Boerhaavia ereeta 

Dalea parryi 

PItaxis neomezioana 

Euphorbia pedioulifera 


Feotis of. palmeri 

Perltyle oallfomloa 

Perltyle emoryi 

Physalis sp. 

Tidestroaia lanuginosa 

Total species in quadratt 37 


78

Figure 17. South-faoing slope at north end of Bahfa San 

Pedro. Bursera mlcrophylla (center), Jatropha 

ouneata. Ruellla penlnsularls. Jatropha ouneata. 

Cordla parvlfolia. Lemaireooereus thurberi. and 

Cameglea glgantea.

TABLE 13 

PLOT 13* BAHIA SAN PEDRO, CA. 1/2 KM. INLAND (NORTH) FROM 

SHORE AT NORTH END OF BAY, Cl. 8 M. ELEV. PEDIMENT OF VOL 

CANIC ROCK WITH FEW SHALLOW POCKETS OF SOIL. NORTHWEST 

EXPOSURE, 330°, SLOPE 12%, COVERAGE CA. 3fj%, 19 JANUARY 

1965 """ 

Species 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Aoaola willardlana 40 10.2 8.8 

Lemaireooereus thurberl 9 10.0 - 

DIphyaa oooidentalIs 4 9.6 8.0 

Mimosa laxiflora - 7.6 4.9 

Carneglea gigantea - 7.2 - 

Fouquierla diguetli 99 7.2 6.9 

Olneya tesota 1 7.1 - 

Bursera mlcrophylla - 6.6 5.8 

Marsdenia edulls 7 * 6.4 - 

Antigonon leptopus 10 6.3 mm 

Adella obovata 6 6.2 5.9 

Desmanthus oovillei 3 6.1 - 

Colubrina glabra - 5.2 - 

Caesalplnia pumlla 15 5.1 3.7 

Solanum hindslanum 3 4.8 3.7 

Croton sonorae - 4.7 3.0 

Lyoium sp. 8 4.6 - 

Jatropha ouneata - 4.5 4.0 

Meloohla tomentosa - 4.4 3.6 

Opuntia versicolor 18 4.3 - 

Paohyoereus prlnglel - 4.1 

Beloperone callfornloa 7 4.0 - 

Janusia oalifornioa 16 4.0 - 

Jacquemontla sp. - 3.9 - 

80

TABLE 13— Continued 

Kramerla aonorae - 3.8 3*2 

Randla thurberl 3 3.4 

Janusla gracilis 19 3*3 

Ferrocaotus sp* 1 3,0 

A but lion lnoanum 5 2»9 

Berglnla vlrgata 8 2.8 

Trlxls oaliforaloa 5 2.8 

Agave (Euagave) sp* 2 2*7 2*5 

Enoella farlnosa - 2, if 

Slmmondsla ohlnensls - 2*3 

Thryallls angustlfolla 10 1*4- 

Hibiscus denudatus 20 1.3 * - 

Carlowrightia sp* - 1*2 

Wllooxia striata 1 0*8 

Eohinooereus of* engelmannli - 0*6 

Mammillaria sp* - 0*3 

Struthanthua hahkeanus 9 

Total 329 


Aristida adsoenslonls 

Boerhaavla ereota 

Bouteloua sp* (perennial) 

Cathestioum ereotum 

Dltaxls neomezloana 


Panioum arizonloum 

Perityle palmer1 

Setarla liebmannii 

Sympeteleia rupestris 


Total speoleB in stands 51 

81

enoountered along the margins and nearby in the same stand* 

Aoaola wlllardlana and Fouqulerla dlguetll are the most 

numerous and important perennials. Host of the major 

perennials present do not reaoh maximum size, presumably 

as a result of the poor soil condition. The few giant 

oaoti, «•£•» Carneglea glicantea and Paohycereus prlnglel. 

appear as stragglers from nearby south and west-faoing 

slopes* 

Riparian* —Semi-riparian floodplains, arroyos and 

oanyons in the vicinity of Bahfa San Pedro support low 

thornsorub-like forests* 

Major arroyos leading out of the mountains behind 

the bay form floodplains of varying widths with thin 

forests of Lyslloma Candida (Palo Blanco)* Plot 14, Table 

14, Fig* 18* The soil is characteristically deep, and 

consists largely of sand and gravel with a well developed 

litter of leaves and humus. Forty-nine species are present 

in the stand and 47 of these ooourred within the limits of 

the quadrat* Lyslloma produces a nearly closed oanopy of 

lacy green foliage* Beneath the upper stratum of trees is 

a heterogeneous understory of shrubs, sparse enough to 

walk through, and a third layer of herbs near the ground 

is vaguely dlsoernlble and of minor significance* Vines 

are more prominent than in the nearby desertsorub and are 

represented by 8 species (l6j£ of the species present)* 

82

TABLE 14 

PLOT 14. BAHIA SAN PEDRO, CA. 1 KM. INLAND (EAST) PROM 

NORTE END OF BAY, CA. 8 M. ELEV. FLOODPLAIN• SANDY-LOAM 

SOIL WITH TRANSPORTED ROCK. COVERAGE CA. 80^. 17 JANUARY 

1965 "" 

Maximum Mean 



Lysiloma oandida 124 25.5 19.3 

Visoainoa geniculate 11.2 9.4 

Ceroidium floridum 16 9.1 8.9 

Bursera miorophylla 6 8.4 mm 

Colubrina glabra 24 8.4 8.1 

Beloperone oallfomioa 366 7.6 6.7 

Hyptis emoryi - 7.5 6.1 

Abutllon lnoanum 114 6.5 5.1 

Marsdenia edulis 4 6.5 - 

Solatium hindsianum 30 6.3 6.3 

Goseypium klotzchlanum 4 6.0 - 

Forohaomeria watsonli - 5.9 - 

Cardiospermum ooriudum 2 5.7 - 

Janusla oalifomiea 184 5.6 - 

Krameria sonorae 22 5.6 tm 


Meloohia tomentosa 56 5.4 5.3 

Matelea oordifolia 4 5.4 - 


Ditaxis laneeolata 32 5.2 - 

Simmondsla ohinensis 8 5.2 - 

Jatropha ouneata 20 5.1 - 

Abutllon oalifomioum 4 4.8 - 

Lyoium sp« 6 4.6 - 


83

TABLE 1*4-—Continued 

Janusla gracilis 30 

Ruellia peninsularIs 20 

Tragia amblyodonta 4 

Enoella farlnosa 16 

Opuntla versicolor 16 

Trlxls callfornloa 112 

Ferrooaotus sp. 8 

Hlblsous denudatus 12 

Jacquemontla sp. 2 

Lyrocarpa ooulterl 90 

Indigofera laevls 4 

Thryallls angustlfolla 26 

Carlowrightla sp. 56 

Carneglea glgantea 

Hammlllarla sp. 8 

Elytrarla lmbrloata 32 


Total 1510 


Boerhaavia sp* 

Coreooarpus sp. 



Kallstroemia grandiflora 

Mentzella adhaerans 

Perltyle oalifornioa 


Total speoles in stand: 49

Figure 18. Floodplain oa, 2 kms* inland from shore at 

Bah£a San Pedro. Lyslloma oandlda (Palo 

Blanoo)•

Aphyllous and succulent plants, with minor exceptions, are 

absent and the oommoner plants tend to have relatively 

large and thin leaves. The water oourses generally form 

broad sand and gravel washes with little vegetation other 

than sparse growth of Hyptls emoryl and other oooaslonal 

shrubs. 

Stream oourses In deep and narrow rook canyons at 

the base of the mountains support dense tangles of green 

thornsorub* A representative stand was sampled at the 

base of the mountain approximately 1 km* inland from the 

south end of the bay (Plot 15» Table 15t Fig* 19)* The 

understory shrubs merge with the taller elements and both 

are laced with vines which together with thorny habit of 

many of the species make the scrub nearly impenetrable. 

Barren bedrock Is exposed along parts of the oanyon bottom 

and soil pockets are of moderate depth* The relatively 

low stature of many of the common species seems rather 

discordant with the general rlohness of the stand and may 

be due to the shallow soil* The solid bedrock is generally 

barren, except for saxloolous species suoh as Flcus palmer1* 

Ephemeral or annual herbs are soaroe and generally limited 

to small sandy places In the streambed* Some have northern 

affinities (Sonoran Desert) but many are phytogeographlo- 

ally aligned with regions of subtropioal scrub to the south* 

86

TABLE 15 

PLOT 15. BAHIA SAN PEDRO, CA. 1 KM. INLAND (EAST) PROM 

SOUTH END OP BAY, CA. 30 M. ELEV. BOTTOM OF DEEP CANYON 

WITH EAST-WEST AXIS, CANYON FLOOR CA. 5 M. WIDE. GRAVEL 

SOIL AND EXPOSED VOLCANIC BEDROCK. COVERAGE CA. 85%. 

11 NOVEMBER 1965 

Maximum Mean 


Species (125m*) (ft) (ft) 

Erythea elara - 28 - 

Flous palmer1 - 21 - 

Acaoia willardiana 6 19 14.7 

Coursetla glandulosa 5 9.9 - 

3aplum biloculare 6 9.3 7.3 

Lysiloma dlvaricata 3 9.2 7.9 

Buraera microphylla 5 8.8 8.0 

Marsdenia edulis 2 8.8 mm 

Celtis pallida 1 8.3 - 



Diphysa occidentalis 5 8.2 mm 

Cordis sonorae - 7.6 - 

Guaiaoum ooulteri 1 6.3 mm 

Solarium hindsianum 2 6.2 - 

Simmondsia ohinensis 2 6.1 5.6 

Fouquieria diguetii 1 5.7 - 

Cardiospermum ooriodum - 5.6 - 

Melochla tomentosa 5.4 - 

Acalypha californioa 3 5.1 mm 

Tragia amblyodonta 3 5.1 - 

Desmarithus oovillei 2 4.8 mm 

Ditaxis lanoeolata 8 ^•7 - 

Visoainoa geniculata 2 4.6 - 

87

TABLE 15—•Continued. 

Jacoblnla ovata 1 4.1 

Croton sonorae - 4*0 

Euphorbia tomentulosa 29 4.0 2*9 

Abut lion lnoanum 2 3*9 

Brlokellla ooulterl 8 3.7 

Beloperone oallfornloa 16 3.4 

Bursera lazlflora 1 3,J* 

Buellla oallfornloa 2 3.3 

Trills oallfornloa 10 3.3 

Bourerrla sonorae 1 3.2 

unidentified Asolepladaoeae 

(vine) 2 2*9 

Calllandra rose! 1 2*8 

Jatropha cuneata 1 2.5 

Dlcllptera resuplnata 2 2.2 

Lyrooarpa ooulterl 10 1,7 

Opuntla versicolor 1 1.5 

Physails sp. (perennial) 1 1.3 

Hofmelsteria orassifolia 4 1.1 

Elytrarla lmbrloata 3 0«4 

Total 170 




Indlgofera laevls 

unidentified Gramlneae 


Total speoles In quadrat: **3 

Total speoles In stand: 48 

88

Figure 19. Canyon at south end of Bahfa San Pedro at oa. 

1.5 Urns. Inland from shore; looking northwest.

Summary*--The Guaymas region supports rloh and 

varied desertsorub and thomsorub communities. Mangroves 

occur in the protected bays and esteros. Thomsorub com 

munities are rioh in growth-forms and numbers of species. 

Xerophytic desertsorub communities dominated by Larrea 

dlvarlcata and Jatropha cuneata oocur in limited areas at 

low elevation between Guaymas and Bah£a San Carlos. An 

extensive area of thomsorub ooours through the higher 

elevations of the Guaymas Monadnock and extends to low 

elevation through riparian and semi-riparian drainageways 

and on north-facing slopes. Many subtropical elements 

ooour in the thornscrub and thornscrub-llke communities 

and reach their northernmost limits here. 

Vegetation in the vicinity of Bahfa San Carlos and 

Guaymas is somewhat more xerophytlc than at Bah£a San 

Pedro, and northward from Bahfa San Pedro conditions again 

become more arid. 

90

I SLA SAN PEDRO NOLASCO 

This very rugged and precipitous island lies in 

deep water approximately 30 kms. northwest of Guaymas. It 

oonsists of a narrow north-south oriented mountain (Figs. 

20 and 21) 3*5 kms. long and not more than 1*5 km* wide 

(Tamayo, 19^9)> and embraoes approximately 3.0 kms. A 

prominent crest( reaching a peak elevation of 315 m. 

(Tamayo, 19**9)» runs along most of the length of the 

island. On either side of the ridge-crest the terrain 

qulokly falls away into the sea. There are many short 

and steep canyons but no alluvial plains or fans. The 

shore is precipitous and the only beaoh is in a tiny oove 

at the southeast side of the island. Sheer cliffs and 

barren rock slopes reach directly down to the water and 

thus halophytio shore plants are absent. Along the entire 

east side of the island there are only two landfallss one 

at the above mentioned oove and the other at approximately 

one-third the distanoe from the north end of the island. 

The northeast landfall provides the best access to the 

island and the quadrat studies were made above it. 

The island lies 8 kms. west of Bah£a San Pedro 

with a channel of 170 fathoms (Shepard, 1950» Chart IV). 

San Pedro Nolasco consists of granodiorite and is prob 

ably related tjp the small granodiorite area, described by 

91

Figure 200 East side of Isla San Pedro Nolasoo seen from 

Bahfa San Pedro*

Figure 21* Aerial view of east side of Isla San Pedro 

Nolaaoo.

Anderson (1950) on the opposite Sonoran mainland, at very 

nearly the same latitude. Both are apparently of pre- 

volcanic age (Anderson, 1950)* 

The general physiognomy of the island and Its 

vegetation are unique and do not olosely matoh that of the 

opposite Sonoran ooast or any of the other Sonoran islands. 

Its isolation from the mainland oertainly must have been 

long, and it seems logical to infer that the present-day 

biota has reached the island by overwater means. 

of lizardst 

The known herpetofauna consists of five speoles 

Cnemldophorus baoatus 

Ctenosaura hemllopha 

PhvllodaaFylus homolepldurus nolasoensls 

Soeloporus olarkl olarkl 

Uta nolasoensls 

The Ctenosaura and Soeloporus are not taxonomloally dis- 

tinot from mainland populations while the other three taxa 

are endemio. The terrestrial mammal fauna is comprised. 

solely of two endemio Peromysous: P. boyll glasselll and 

P. pembertonl. The endemio vertebrate taxa are closely 

related to the Sonoran mainland fauna. 

Fifty-one speoles of vasoular land plants have been 

collected on the island (Appendix A). Most of the flora 

also oocurs on the opposite Sonoran mainland. Endemics 

are represented by two species of oaotii Echlnooereus 

websterlanus and Mammlllarla multldlaltata. Agave

ohrvsoglossa. onoe thought to be endemlo to the island, is 

now known from the opposite Sonoran mainland and a similar 

appearing population also ooours on Isla Tlburon. Speoies 

occurring as outlying populations from Baja California are 

Euphorbia maadalenae. Hofmeisterla laphamlold.es plurlseta, 

Mammlllarla evermannlana« and Salvia elmllla. (Euphorbia 

magdalenae is reported from Bahfa San Pedro by Johnston, 

1924, but I have been unable to looate it there, either in 

the field or in the collections of the California Academy 

of Solenoes.) Metastelma prlnglel occurs in Baja Cali 

fornia as well as in Sinaloa (Wiggins, 19*K>) but the 

Nolaseo population is the first record for Sonora. The 

platyopuntla on Nolaseo, tentatively referred to as Qpuntla 

bravoana (see Wiggins, 1964), also ooours in Baja California, 

on several small islands in Guaymas harbor, and on the 

ooastal plain south of Guaymas and southward into Sinaloa, 

but it is not found on the mainland north of Guaymas* 

These extralimital populations are generally restricted to 

higher elevations at the east side of the island. Their 

presence here seems to be due to the looally favorable 

conditions in this part of the island. A high east-facing 

slope bordering the sea is physloally not duplicated on 

the adjacent west ooast of Sonora and this may explain 

their absenoe there. 

95

In addition to the endemios mentioned above the 

populations of Mammillaria evermanniana and Salvia Blmills 

show minor morphological variation, hut doubtfully warrant 

subspeoiflo recognition. Thus a total of ** speoies, nearly 

ence. 

of the flora, show some degree of evolutionary diverg 

Ephemeral speoies are represented by Ik speoies or 

27*5/6 of the total flora* Amaranthus fimbriatus and 

Boerhaavla sp« are primarily summer-fall speoies while 

Parletarla florldana is a winter-spring ephemeral. The 

remaining ephemerals are non-seasonal and appear with 

both summer-fall and winter-spring rains* 

The majority of species on the island have small, 

simple leaves and some are aphyllous. There are only two 

speoies with compound leavesi Bursera mlerophvlla and 

Aoacia wlllardlana. Most of the leaf-bearing species are 

drought-deciduous* Agave chrysoglossa. the only true ever 

green speoies present, has succulent leaves. Several 

species are tardily drought-deciduous but become leafless 

or nearly so in time of severe drought, e.g., Flous 

palmerl. Hofmelaterla crasslfolla. and Slmmondsla chlnensls. 

Environmental and vegetational gradients on the 

island are sharply delimited. Corresponding with abrupt 

topographic changes the vegetation sometimes shows a 

mosaic-like pattern and vegetational contrasts on 

96

different exposure gradients are among the most striking 

enoountered anywhere in the Gulf Coast of Sonora* On the 

east side of the island and at higher eleTation there is 

a general trend towards relatively less xerophytio vege 

tation and an inorease in number of species* 

North Slopes.--»The north and northeast-facing 

slopes on the east side of the island are oovered with 

dense fields of grasses and forbs (Plot l6f Table l6v Fig* 

22)• One of the most evident features of these north 

slopes is the unbroken and continuous oover of topsoll, 

even on steep slopes* £*£*, a k5% slope in Plot 16* The 

soil is relatively deep, rich in humus, and loose* It is 

evident that the dense herbaceous fields not only build up 

the soil but prevent its erosion* The substratum is so 

loose and steep that major perennials. Including oaoti if 

present* would probably topple over before reaohing matur 

ity* Total ooverage of herbaceous species is approximately 

90 to 100^, while non-herbaceous perennials aooount for 

less than 5% coverage* Nine of the 16 species present 

are herbaoeous* Non-herbaceous perennials are weakly 

established and are stragglers from adjacent slopes, e.g., 

Pedllanthus* Simmondsla and Vlgulera. Jatropha cuneata 

and the few cacti are waifs from nearby slopes of differ 

ent exposure and do not reaoh reproductive size* It is 

evident that the greatest biomass productivity (per unit

TABLE 16 

PLOT 16. I SLA SAN PEDRO NOLASCO, EAST-CENTRAL SIDE, CA. 

100 M. ELEV. NORTH EXPOSURE, 3^0-3600, SLOPE 45*. SOIL 

LOOSE, ROCKY, RELATIVELY DEEP, AND WITH MUCH HUMUS. COVER 

AGE CA. 95% INCLUDING GRASSES AND FORBS, CA. 5% EXCLUDING 

GRASSES AND FORBS. 18 JANUARY 1^5 

Mali WW Mean 


Speoies (0.1 ha) (ft) (ft) 

Viguiera deltoidea 9 5.9 5-0 

SisuBondsia ohinensis 9 5.* 5.1 

Pedilanthus maorooarpus 6 3^ 2.4- 

Opuntia of. bravoana 2 3.8 2.7 


Paohyoereus pringlei 1 1.6 - 

Manual liar ia multidigitata JL 0.3 - 

Total 35 


Amaranthus finbriatus 


Coreooarpus arizonious 

Cusouta maorooephala 

Muhlenbergia niorosperma 

Parietarla floridana 

Perityle oalifornioa 

Setarla palmeri 

Vaseyanthus insularis 


Total speoies in stands 16 

98

Figure 22# Northeast side of Isla San Pedro Nolasoo* North- 

facing slope Kith grasses, Amaranthus flmbrlatus. 

and few scattered shrubs of Vlgulera deltoldea. 

Lenalreooereus thurberi and Paohyoereus prlnglel 

on opposite south-faolng slope.

area per unit time) oil the island ooours on these north 

slopes; most of it is seasonal and oan be attributed to 

several speoies( £•&•, Amaranthus fimbriatus. Coreooarpus 

arlzonlous. Muhlenbergla mlorosperma. Setarla palmerl. and 

Vaseyanthus Insular!s. 

South Slopes.—The south-faolng slopes are rugged, 

greatly eroded, and with much exposed bedrock. Although 

there is little build-up of soil the rook surfaoe is suf 

ficiently weathered to allow ample root-penetration. 

South slope vegetation (Fig. 22) consists largely of col 

umnar cacti (Lemalreocereus thurberl and Pachyoereus 

prlnglel). a sparse understory or desert shrubs, e.£«, 

Jatropha ouneata and Vlgulera deltoidea, and smaller cacti 

(Eohlnocereus websterlanus and Mammlllarla multldlgltata)• 

Ephemeral3 are poorly represented and are often absent. 

Only a few ephemeral species have been found on south-faolng 

slopes, e.£., Boerhaavla. Coreooarpus. and Vaseyanthus. and 

all of these reaoh greater development on other slopes and 

generally are mere stragglers here. 

East Slopes.—The richest and most diverse vegeta 

tion on the island occurs on east-facing slopes (Plot 17, 

100 

Table 1?, Figs. 23, 2kf and 25; Plot 18, Table 18, Fig. 26). 

The east slopes consist primarily of broad ridges whloh 

separate north and south-facing canyon slopes and degree of 

slope is seldom so steep as on other slope exposures.

TABLE 1? 

PLOT 17* ISLA SAN PEDRO NOLASCO, EAST-CENTRAL SIDE, CA. 

140 M. ELEV. EAST EXPOSURE, 95° • SLOPE k8%. LOOSE R

Figure 23• Northeast side of Isla San Pedro Nolasoo* East- 

faolng slope* Aoaola wlllardlana. Agave ohryso- 

gloasa, Eohinooereus wetasterlanua. Lenalreo- 

oereus thurberl. Qpuntla of* bravoana, Paohyoereus 

pringlel* and Vl«ulera deltoldea.

102

Figure 24* Northeast side of Isla San Pedro Nolasoo. East- 

facing slope. Aoaola wlllardlana. Agave ohryso- 

glosaa. Eohlnoeereus websterlanus. Leaalreooereus 

thurberl. Manual liar la multldlaltata. and Paohy- 

oereus orlnglel.

103

Figure 25. Northeast side of Isla San Pedro Nolasoo. 

East-facing slope. Eohlnooereus websterlanus 

and Mammlllarla multldlgltata.

104

TABLE 18 

105 

PLOT 18. ISLA SAN PEDRO NOLASCO, EAST-CENTRAL SIDE, 270 M. 

ELEV. (CA. 25 M. BELOW CREST*) EAST EXPOSURE. 1050, SLOPE 

57% • SHALLOW ROCKY SOIL. COVERAGE CA* 35%. 18 JANUARY 1965 

Speoies 

Number 

(500m 2 ) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Aoaoia wlllardlana 2 16.8 mm 

Paohycereus prlnglel 1 14.9 - 

Fouquleria diguetll 13 12.2 12.0 

Lemaireooereus thurberi 5 10.7 7.2 


Viguiera deltoidea 62 6.2 5-4 

Simmondsia ohinensis 15 5.3 - 

Bernardia sp. - 5.1 

Bursera mlcrophylla 9 4,0 - 

Jatropha cuneata 1 3.1 - 

Opuntia fulgida 4 2.9 - 

Agave ohrysoglossa 2 2.7 - 

Pedilanthus maorocarpus 66 2.7 2.6 

Trixis oalifornica 13 2.4 - 

Opuntia of. bravoana 1 2.2 - 

Eohlnooereus irebsterianus 22 - - 

Mammlllarla multidlgltata 85 mm - 

Total 303 



Aristlda adsoenslonis 

Coreooarpus arizonlous 

Muhleribergia mlorosperma 

Perityle oalifomloa 

Setaria palmerl 

Vaseyanthus insularis 


Total speoies in stands 24

Figure 26. East alope at orest of Isla Saa Pedro Nolasoo* 

Acacia wlllardlana. Lemalreooereus thurberi. 

and Vlgulera deltoldea.

106

Erosion Is evident and where soil Is not held In plaoe by- 

rocks and roots It Is quickly carried away leaving "barren 

rook. Erosion frequently undermines the larger oolumnar 

107 

oactl as well as other plants and speolmens thusly uprooted 

are not unoommon. East slopes are oharaoterlzed by a rloh 

growth of stem and leaf succulents, desert shrubs and herbs. 

Agave ohrvsoglossa and Qpuntla (Platyonuntla) of, bravoana 

are nearly confined to east slopes. Major perennials 

together with the herbaceous species produce more than 5®% 

cover and much of the open area Is exposed bedrock. At 

Plot 17, located at oa. IkO m. elevation, 20 species were 

present while at Plot 18, at oa. 270 m. elevation, 2k 

species were present. 

Crest and West Slopes.--The vegetation on the west 

slopes of the island olosely resembles that of the south- 

faoing slopes of either side of the island. The west side 

(Fig. 27) is more rugged and eroded than the east and 

appears to be without unique species. Plot 19 (Table 19» 

Fig. 28) was located on a small, steeply sloping H benoh M 

near the top and west side of the island. The most oons- 

piouous elements were columnar cacti, e.£., Lemalreooereus 

thurberi and Pachyoereus prIngle1 (Fig. 28), desert shrubs, 

£.«£•> Jatropha cuneata and Vlgulera deltoldea. and small 

oactl, £.&•» Echlnooereus websterlanus and Mammlllarla 

multldlgltata.

Figure 2?. Northwest side of Isla San Pedro Nolasco. 

Lemaireooereua thurberi and Paohyoereus 

pringlel. Fouquierla dlguetil (leafless, 

oenter foreground).

'0 

108

TABLE 19 

109 

PLOT 19. ISLA SAN PEDRO NOLA.SCO, WEST-CENTBAL SIDE, CA. 

270 M. ELEV. (CA. 25 H. BELOW CBEST.) SOUTHWEST EXPOSURE, 

235°. SLOPE 58jC SHALLOW ROCKY SOIL. COVERAGE 20J*. 18 

JANUARY 1965 

Speoies 

Number 

(500m 2 ) 

Maximum 

height 

(ft) 

O 

. 

o 

Mean 

height 

(ft) 

H 

Pachyoereus pringlei 5 14.8 12.7 

Lemalreooereus thurberl 

Fouquleria diguetii 

17 10.8 

5 

10.0 

m 

Colubrina glabra 2 6.5 5.

Figure 28. Northwest side of Isla San Pedro Nolasoo near 

crest. Lemalreooereus thurberl and Paohyoereus 

prlnglel* Vaseyanthus InsularIs ollmbing on 

Lemalreooereus (left)*

110

Ill 

Vegetation along the crest of the island (Plot 20, 

Table 20) olosely resenbles that of the west-facing slopes 

at higher elevation (e«g,, Plot 19)* 

Summary# —The interrelation of climax vegetation 

to slope exposure, soil profile, and erosion are unusually 

clear on Xsla San Pedro Nolasco. The vegetation is com 

prised of desertsorub sharply divided into distinotive com 

munities distributed acoording to slope exposure} north 

slopes Kith meadows of grasses and forbs; east-facing 

slopes with rich growth of suooulents, shrubs, grasses, 

and forbs; and south- and west-faolng slopes with stem 

suoculents and xerophytic shrubs* 

Por the most part the biota show closest relation 

with the opposite Sonoran coast; however, a number of 

plant species are otherwise known only from Baja Cali 

fornia and mainland regions at lower latitudes. Endemic 

taxa include three lizards, two rodents, and two species 

of caotl*

TABLE 20 

PLOT 20* ISLA. SAN PEDRO NOIASCO, RIDGE-CREST, CA. 300 M. 

ELEV. NEARLY LEVEL TERRAIN* ROCKY SOIL. COVERAGE CA. 50 jt. 


Speoies 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Aoaola villardlana • 17.0 _ 

Paohyoereus prlnglel 8 11.3 - 

Pouquleria diguetli 24 10.1 - 



Vlgulera deltoldea 76 5.6 5.1 

Simmondsla ohinensls 24 4.3 4.2 

Opuntia fulglda 124 4.2 4.1 

Bernardla sp* 4 3.1 - 

Pedilanthus macrooarpus 96 2.9 2.5 

Trills oallfomloa 20 2.9 2.3 

Coreooarpus arlzonious 8 - 

Eohlnooereus websterlanus 24 - - 

Mammlllarla multldlgltata 

724 

Total 1140 


Arlstlda adsoenslonis 

Aristlda sp. (perennial) 

Bouteloua aristidoldes 

unidentified Gramineae 

Total speoies in quadrats 1? 

Total speoies In stands 18 

112

LLANURAS DE SAN JUAN BAUTISTA 

A great plain oalled the Llanuras de San Juan 

Bautlsta stretohes aoross the ooast of Sonora from the 

violnity of Bahfa Kino south to Estero de Tastlota. It 

is formed of Quaternary sediments and seems to have an 

eroslonal history similar to that of the expansive ooastal 

plains south of Guaymas (see Allison, 196*0• The deep 

alluvial soil of the Llanuras, as well as that of the 

plains south of Guaymas, is of major agrioultural import* 

anoe and today little remains whloh is not under irriga 

tion exoept for parts of the ooastal margin* The region 

is therefore populated and is the most severely altered 

113 

portion of the Gulf Coast of Sonora. Muoh of the remaining 

vegetation has been seriously depreoated by cattle grazing 

and by leneros (woodcutters) who have made innumerable 

trackless roads into the onoe extensive mesquite forests 

and other areas. 

The R£O Sonora enters the Llanuras but its flow 

is ephemeral and surface waters seldom, if ever, reaoh the 

sea today. Shepard (1950) suggests that the broad and 

relatively shallow-water shelf along the ooast is the 

result of a sinking delta. Shreve (1951) also suggests 

deltaic origin of the Llanuras. It therefore seems that 

a river, or rivers, once oarrled water to the ooast aoross 

the Llanuras.

Beaoh dunes, often 10 to 15 m* high, border the 

entire shoreline except locally at Cerro San Nloolaa and 

at the three estero outlets* Generally there Is an outer 

series of high and unstable dunes and an inner series of 

lover and more stabilised dunes. The three major outlets 

for watercourses in the Llanuras are Estero de la Cruz in 

the north which empties into Bahla Kino, Estero de Punta 

Baja at about midway, and Estero de Tastlota in the south* 

From Cerro San Nicolas (at the south end of Bahfa Kino) to 

Punta Baja, a dlstanoe of approximately 30 Ions*, there are 

in* 

high dunes along the entire coast blooking any dlreot drain 

age to the sea* Thus the soil of the low flats behind the 

dunes oontalns a relatively high concentration of salts* 

Plantless salt flats surround muoh of Estero de la 

.. Cruz but suoh areas are greatly reduced at Punta Baja and 

Tastlota. These barren flats are most extensive towards 

the south end of Estero de la Cruz and reach nearly a 

kilometer In width. Here the fall of the terrain is 

almost imperceptible. Water from the estero may briefly 

Inundate the flats; however, for most of the year the sur 

face is dry with a hard and shiny orust of salt* It appears 

that the soil is too dry to sustain or allow the establish 

ment of littoral scrub and too poorly drained for Frankenla 

sorub. Littoral scrub occurs on the estero or lower side 

of the salt flats while inland and at slightly higher

elevation the first vegetation to be enoountered consists 

of Frankenla palmerl and Allenrolfea oooidentalls. Where 

the elevational gradients are steeper, e.g., at the west 

ern margin of the estero, Prankenla scrub lntergrades with 

littoral scrub and a plantless zone does not exist. 

Proceeding inland from the ooastal dunes several 

series of low and presumably older dunes are usually 

encountered. These are stabilized and would not be recog 

115 

nized as being derived from dunes exoept by their proximity 

to the shore, decreasing height as one proceeds inland, and 

long axis parallel to the coast. Throughout the Llanuras 

a repetitive pattern of slightly undulating terrain is 

found. The difference in elevation may be very slight, 

£•£•• less than one meter, but it is reflected in very dif 

ferent vegetatlonal structure over small distances, £•£•, 

several meters. Fossil marine mollusks representing modern 

Gulf Coast forms can be found over wide regions of the 

Llanuras. 

Cerro San Nloolas Juts out on a broad peninsula at 

the south end of Bahfa Kino and but for a few meters of 

elevation of the surrounding saline flats it would be an 

island muoh the same as Isla Alcatraz. Its granitic struc 

ture, physiognomy, size, and position along the ooast 

reminds one of Cerro Tepopa and the granitic understruoture 

of Cerro Prleto to which it may be related geologically.

Unfortunately the biota of Cerro San Nicolas and Cerro 

Tepopa are poorly known. 

116 

Throughout the length of the Llanuras a relatively 

oonaistent pattern of transition was noted from the shore 

to the interior and from lowest to highes terrain* A series 

of sample stations near Punta Baja will serve as a basis for 

the description and oomparison of the vegetation of the 

Llanuras region* 

Punta Ba.1a 

Approximately midway between Cerro San Nicolas and 

Estero de Tastlota the coastline of the Llanuras forms a 

prominent point called Punta Baja* There are poor dirt 

roads leading to it and some oattle grazing nearby but the 

vegetation nearest the mouth of the estero is relatively 

little disturbed. At the north side of the entranoe to 

the estero is a dense stand of oardon (Paohvcereus prlnglel) 

on a sand hummook and this place is oalled El Cardonal• 

Estero*—The estero at Punta Baja as well as 

Estero de la Cruz and Estero de Tastlota support dense 

stands of mangrove along their peripheries* All three 

speoies of mangroves are presents Avlcennla germinans, 

Laguncularla raoemosa, and Rhlzophora mangle. Avloennla 

is the most abundant of the three and oomprlses the major 

portion of these mangrove communities* In oontrast to

the mangrove esteros in the Tiburon and Guaymas regions, 

those of the Llanuras have muoh open water and mangroves 

oover only a minor portion of the estero. 

Bordering the mangroves and intermingling with the 

uppermost Avioennla Is the usual array of suoculent halo- 

phytes and salt grasses. These form dense and evergreen 

mats in the low and wet tidally inundated saline soils. 

Charaoteristlo species here are: 

Allenrolfea oooldentalls 

BatIs marltlma 

Mavtenus phvllantholdes 

Monanthoehloe llttoralls 

Salloornla paolfloa 

Sesuvlum verruoosum 

Sporobofus vlrglnlous 

Suaeda torreyana 

117 

Dunes.—-The outer coastal dunes are generally 10 to 

15 m. and consist of shifting sands with steep and usually 

barren lee slopes (Fig. 29). Dunes of different height 

show marked vegetational differences. A quadrat study site 

on an outer shifting dune was chosen at approximately 1 km. 

north of the entrance to the estero (Plot 21, Table 21). 

Low and spreading perennials, including succulents and salt 

grass, are oharaoteristio of the windward slopes, extending 

from near the high tide line to the dune crest, e.g., 

Abronla marltlma. Atriplex barolayana. Sesuvlum verruoosum. 

and Sporobolus vlrglnlous. Euphorbia leucophylla and Croton 

callfornlous« common dune-adapted speoles, are especially

Figure 29. Aerial view of coastal dunes several kilometers 

north of Punta Baja. Note unstable beaoh dunes 

engulfing Paohyoereus prlnglel*

118

TABLE 21 

PLOT 21. PUNTA BAJA, CA . 1 KM. NORTH OF 

SHIFTING BEACH DUNE CA. 12 M. HIGH, NEAR 

CA. 153C 17 FEBRUARY 1965 

Species 

Number 

(0.1 ha.) 

MOUTH OF 

CREST. 

ESTERO. 

COVERAGE 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Paohyoereus pringlel r» 9.6 m 

Prosopls torreyana 2 8.1 7.1 

Lyolum sp. 2 6.4 5.2 

Jatropha ouneata - 5.7 4.4 

Maytenus phyllantholdes 1 5.3 - 

Opuntla fulglda - 5.0 - 

Atrlplez oanesoens 4.8 4.2 

Jatropha oineara 1 4.6 - 

Sphaeraloea sp. - 3.5 - 

Viguiera deltoldea - 2.4 2.1 

Croton oalifornioa 43 2.3 - 

Dalea emoryi - 2.3 - 

Allenrolfea oooidentalls 27 2.1 - 

Atrlplez barolayana 2 1.8 - 

Sporobolus virginious mm 1.4 - 

Helianthus niveus - 0.9 - 

Euphorbia leucophylla 37 0.7 - 

Sesuvium verruoosum - 0.7 - 

Abronia maritima 0.4 w* 

Total 124 


Dalea mollis 

Datura disoolor 

Diooria oanesoens 

Palafoxia linearis 

Total species in quadrat 14 


119

abundant on top of the dunes* Epheaerals are represented 

by relatively few speoles but these often form large popu 

lations, £•£•» Dloorla oanesoens. and Palafoxla linearis* 

Both ephemeral and perennial dune speoles oommonly develop 

deep roots. Dloorla. apparently oonflned to the ooastal 

120 

dunes, often outnumbers all other plants on the dunes. The 

young plants qulokly develop deep tap roots many times 

longer than the shoot* When Dloorla matures and dries it 

breaks off at an absolsslon layer at ground level and 

beoomes a tumbleweed, an adaptation whloh has not been 

found among any other native speoles in the Gulf Coast of 

Sonora* The moving dunes sometimes leave small, high, and 

oonioal-shaped hummocks capped with shrubby mats of large 

desert shrubs, ©•£•# Atrlplex oanesoens. Lvolum SP*. and 

ProsoplB torreyana* These shrub-capped hummooks may per 

sist long after the main dune has blown away. 

Inner and stabilized dunes oharaoteristloally 

support extensive stands of Paohyoereus pringle1. Figure 

29 shows the leeward edge of an outer dune engulfing the 

inner dune and many cardons are in various stages of 

engulfment by the shifting sands. The plant is able to 

withstand partial burial and often persists in such a state 

for a number of years. Other major perennials common on 

partially stabilized sands of inner dunes include Jatropha 

olnerea. Qpuntla fulglda var. mammillata. Sphaeraloea sp., 

and Vlaulera deltoldea*

Coast-Shrub Zone (Frankenia).—An extensive zone 

of Frankenia palmer! occurs on the low flats surrounding 

Estero de la Cruz* Southward near the coast between 

Estero Cruz and Punta Baja there are only intermittent 

stands and at Punta Baja it again forms a well marked 

zone. Frankenia has not been found at Tastlota and Its 

ultimate southern limit in Sonora is In the vicinity of 

Punta Baja. 

At Punta Baja maximum development of Frankenia 

sorub ooours on hard-paoked soil near the estero, parti 

cularly on terrain of slight gradient with a western or 

southern exposure* Ephemerals are scant and inolude only 

a few xerophytlc species, 

121 

A quadrat was plaoed In a characteristic Frankenia 

stand at ca. 1/2 km* east of the northeast end of the 

estero (Plot 22, Table 22). This site is ca. 1 km. east 

of the ooastal dunes (Plot 21). The lowest ground in the 

area, consisting of poorly drained and hard-paoked soil, 

supports a low and sparse cover of succulent halophytes 

comprised primarily of Allenrolfea oocldentalis and Suaeda 

torreyana* At the quadrat site whloh is less than 1/2 m* 

higher in elevation the succulent halophytes diminish in 

density and the community stand is dominated by Frankenia 

palmerl whloh exoeeds the other species in total coverage 

and number of individuals. Allenrolfea and Suaeda are

TABLE 22 

PLOT 22. PUNTA BAJA, CA. 1 KM. INLAND (EAST) FROM SHOBE. 

SALINE FLAT BETWEEN LOWSTABILIZED DUNES. HARD-PACKED AND 

FINE-TEXTURED SANDY-SILT SOIL. COVERAGE CA. 15%. 

17 FEBRUARY 1965 

Speoies 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Jatropha oinerea 35 **•7 2.3 

Lycium sp. mm ^•5 - 


Opuntia leptooaulis 4 2.9 2-7 

Suaeda torreyana 75 2.6 2.0 

Atriplex linearis 12 2.5 2.1 

Lyoium sp. 8 2.5 2.5 

Opuntia fulgida 9 2.1* 2.2 

Allenrolfea oooidentalis 178 2.1 1.8 

Prankonla palmeri 3^8 1.8 1.5 

Eupatorlum sagittatum 1 1.2 - 

Viguiera deltoidea mm 0.9 - 

Paohyoereus pringlei 3 0.6 - 

Mammillarla swingle! 12 0.3 0.3 

Total 688 


Bouteloua aristldoides 

Bouteloua barbata 

Cryptantha angustlfolla 


Muhlenbergla porteri 

Peotls of. papposa 



122

common but their greatest concentration within the con 

fines of the quadrat are at its lowest elevation, although 

these elevational gradients are not more than 2 to 3 deoi- 

meters. Small plants of Pachycereus pringle1 are present 

but are clearly derived from nearby populations on higher 

ground* Frankenla continues to be abundant on adjacent 

small sandy hummocks which are 1 to 1.5 m. higher than the 

123 

surrounding flats. Here several species of Qpuntla (cylin- 

dropuntia or cholla) and small shrubs, e.g., Vlgulera 

deltoldea. become common. The height of the middle-lying 

ooast shrub community seldom exceeds 0.5 m. while on the 

higher terrain it commonly reaches 1*5 m. 

Seven species of herbaoeous or ephemeral plants 

are present. However, these are rare, generally localized 

in small depressions at the base of shrubs, and become more 

numerous on higher ground. Nineteen species were present 

within the confines of the quadrat and 21 species in the 

stand. 

Cardonal.—A quadrat study site in the cardonal 

(Plot 23, Table 23, Fig. 30) was located oa. 1.5 kms. 

inland from Plot 22. The terrain here consists of low 

undulating sand-hummocks, apparently derived from stabi 

lized old dunes. The higher ground supports a dense growth 

of cacti of diverse growth-forms and various desert shrubs. 

Pachyoereus pringle1. or cardon, is the largest and most

TABLE 23 

PLOT 23- PUNTA BAJA, CA. 1,5 KMS. INLAND (EAST) FROM SHORE, 

SANDY HUMMOCK OR LOW STABILIZED DUNE. COVERAGE CA. 50%• 

CATTLE GRAZING. 17 FEBRUARY I965 

Species 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Paohyoereus pringlei 11 38 32.3 

Lemalreooereus thurberl 10 21 15.1 

Carneglea gigantea - 16 - 

Prosopis torreyana tm 11.2 10.0 

Lophooereus sohottil 15 10,6 8.7 

Lyoium sp. 18 8.6 7.6 

Atamisquea emarglnata 15 8,1* 7.** 

May tonus phyllanthold.es 83 7.9 6.3 

Opuntia fulgida* 92 7.1 6.0 


Vlgulera deltoidea 59 5.2 4.0 

Abutilon oalifornioum 1 4.7 - 

Opuntia leptooaulls 3 4.4 - 

Jatropha oinerea 87 4.0 3.5 

Frankenla palmer! 10** 1.8 1.5 

Mammillarla sp. 20 0.4 0.3 

Total 519 

Herbs Present* 

Cenohrus palmeri 

Ditaxis neomexioana 




•Abundant small fallen joints from Qpuntla fulgida not 

counted•

Figure 30« Cardonal at Punta Baja, oa. 1 Ion* Inland (east) 

from shore. Paohyoereus prIngle1. Lophooereus 

aohottll. Lemaireooereus thurberl« and Qpuntla 

fulglda mammillata« Pole in oenter is 5 feet*

125

126 

prominent plant here and hence the name oardonal* The low- 

lying terrain between the sandy hummocks supports little 

more than a low sorub of Frankenla palmerl. Although 

Frankenla extends onto the higher ground of the oardonal it 

does so in diminished density and mostly oocurs in open 

areas. 

Caoti represent half of the perennial species. 

Common desert shrubs include drought-deciduous species, 

©,•£•t Jatropha ouneata and Vlgulera deltoidea. and ever 

green or tardily deciduous halophytes, £•£•» Frankenla 

palmerl and Maytenus phyllantholdes. The drought-deciduous 

desert shrubs occur farther inland, where some reach greater 

development, but the halophytio shrubs are here at their 

inland limits. The combination of the cacti and partially 

evergreen halophytes produces an aspect of relatively little 

seasonal variation. Although the vegetation is of "tree 

height" the number of species present is about the same 

as in the Frankenla zone (Plot 22). Species enumerated in 

the stand total 19, and 2 of these did not occur in the 0.1 

ha. quadrat. Cardonal of similar physiognomy occurs near 

the shore throughout the Llanuras region. Proceeding 

inland the dense stands of Pachycereus prlnalel are gradu 

ally replaced by Carneglea gjgantea. 

Mesqultal.—Farther inland the caotus sorub gives 

way to dense and thorny sorub in which mesquite (Prosopls

torreyana is prominent and henoe the term mesquital (Fig* 

31). Many of the oaotus scrub species inoluding Carne«lea 

gjgantea are common at the edges of patohes of mesquital* 

The mesquital is not continuous and interdigltatlng with 

it on slightly lower ground are open flats of hard-packed 

and supporting sparse growth of alkaline-tolerant shrubs, 

12? 

£*&** Atrlplex polycarpa and Suaeda torreyana* which occupy 

a position comparable to the Frankenla sorub between patohes 

of oardonal* 

A sample station was located at ca. 4 kms* inland 

(east) from the shore at ca* 8 kms* north of Punta Baja 

(Plot 2k, Table 24-, Fig* 32)* The terrain is flat and the 

elevational gradients are not readily evident* Dense 

island-like patches of mesquital stretch across the plain 

among open and partially barren flats with Atrlplex and 

Suaeda* Within the mesquital there is a closed oanopy of 

thomscrub-like trees and large shrubs* Where the larger 

trees have been out by leneros and/or where there has been 

overgrazing by cattle, a secondary growth of dense tangled 

splnesoent shrubs has developed. In mesquital which has 

been relatively little disturbed, the undergrowth is more 

open and the upper stratum forms a nearly olosed canopy* 

Such stands, however, are mostly destroyed today. The 

mesquital varies In height and the smaller patohes are 

shrubby with dense tangles of spiny shrubs much like the

Figure 31. Aerial view of mesqultal alternating with 

alkaline flats, several kilometers north 

and inland (east) from Punta Baja.

128

TABLE Zk 

129 

PLOT 24. CA. 4 KMS, INLAND (EAST) FROM SHOBE AT CA. 8 KMS. 

NORTH OF PUNTA BAJA. DESERT PLAIN, HARD-PACKED SILT-LIKE 

ALLUVIAL SOIL. COVERAGE CA. 95%* CATTLE GRAZING. 


Speoies 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Prosopia torreyana 41 oa. 30 - 

Jacqulnla pungens 2 oa.25 mm 

Carnegiea gigantea 5 23.6 22.3 

Lophooereus sohottii 6 13.1 9.9 

Condalia globosa l 12.3 - 

Lyolum sp 31 10.5 10.0 

Condalia lyoioides 2 10.3 - 

Atamisquea emarginata 4 9.3 7.8 

Maytenus phyllanthoides 1 9.3 - 

Koeberlinia splnosa 3 7.3 - 

Lyoium sp. 19 7.3 5.3 

Atriplex polycarpa 29 5.6 4.8 

Lantana sp. 2 5.2 - 

Vallesla glabra 1 4.7 - 


Suaeda torreyana 9 4.3 - 

Abutilon oalIforalcum 8 4.1 - 

Atriplex linearis 21 3-2 2.9 

Croton sonorae 30 3.2 2.8 

Ferrooaotus wislizenii 1 3.1 - 

Trixis oaliforaioa 336 2.8 - 

Viguiera deltoidea 61 2.7 2.5 

Struthanthus hankeanus 4 - - 

Phoradendron diguetianum 1 - mm 

Total 619


Dltaxls neomezloana 

TABLE 2^—Continued. 


Total speoles In standi 25

Figure 32. Saltbush flats at edge of mesquital patch, oa. 

8 kms* north and oa. 4 kms. Inland (east) of 

Punta Eaja. AtriPlex polyoarpa and Suaeda 

torreyana In foreground* Carneglea glgantea. 

Koeberllnla splnosa. Prosopls torreyana.

* ? V I** 

! -V.1/ 1 

*ar~r Si" 

131

132 

seoondary growth of more extensive mesqultal areas. Extenu 

ating oiroumstanoes did not allow time to searoh the vicin 

ity of Plot Zk adequately for total number of speoies 

present and a more thorough investigation should yield 

more than the 25 speoies listed* 

Between the island-like patches of mesqultal are 

broad and partially barren flats of varying size, often 

exceeding the mesquital in area (Figs. 31 and 32) • Plant 

ooverage on these flats is generally less than 10% and 

consists primarily of Atrlplex polyoarpa, A. linearis, and 

Suaeda torreyana. Carneglea glgantea. Ferrocaotus 

wlslizenll. and Qpuntla fulglda ooour at the edge of the 

mesqultal patches and occasionally onto the Atrlplex-Suaeda 

flats* Water may stand for days and sometimes weeks in the 

poorly draining flats of the Llanuras following major rains 

indicating that these partially barren areas are very poorly 

drained. Within the mesquital the soil is covered with a 

duff of twigs and fallen leaves, as well as herbaceous 

ground cover, while that of the Atrlplex-Suaeda flats has 

a hard crust of dried mud. 

Summary.—Desertsorub communities along the coast 

of the Llanuras de San Juan Bautista exhibit strong zona- 

tion parallel with the shore line. Mangroves ooour at 

Estero de la Cruz, Punta Baja, and Tastiota. Major desert- 

scrub communities include dune communities, coast shrub

(Frankenia palmerl)« oaotus scrub with oardonal (Paohy- 

oereus prlri«lci) near the ooast and Carneglea glgantea 

further inland, AtriPlex and Suaeda. and mesqultal* The 

southern limit for the important ooast shrub zone (Frank 

enia palmerl) occurs in the vioinity of Punta Baja. 

133

ISLA ALCATRAZ 

Isla Aloatraz is also known as Isla Tassne or 

Pelloan Island, Tassne Is a corruption of tosnl which is 

the Serl word for pelloano or aloatraz (Moser and Moser, 

13^ 

1961). It is situated in Bah!a Kino and lies nearly 2 kms. 

west of the adjacent mainland shore. The ohannel is not more 

than several fathoms deep (U.3,N. Ocean. Offloe, 1951). The 

area is given as 1.44 sq. kms. by Tamayo (19^9)• 

The east side of the island, comprising roughly 

one half of the area, is low and relatively flat while the 

western portion is rocky and rises steeply to ca. 165 m. 

elevation (figs. 33 and 3^). The Island appears to be 

more arid than the adjacent mainland. 

Isla Aloatraz has not been permanently inhabited 

by man, and the vegetation is essentially original and 

relatively unaltered. There Is no fresh water on the island 

and grazing animals are absent. The non-avian vertebrate 

fauna apparently consist solely of lizards: Sauromalus 

and Uta stansburlana. The ubiquitous Phyllodaotvlus may 

reasonably be expected to be present. Rodents are not 

known from the island and trapping efforts have been 

negative. 

Phvtogeography.—Thirty-eight species and two sub 

species of vascular land plants are reported from the island

Figure 33. Aerial view of Isla Aloatraz; looking north 

west.

135

Figure 3^. Isla Aloatraz, looking west from sandy flat at 

east end of island. Forbs in foreground include 

Amaranthus watsonll, Palafoxla linearis, and 

Snhaeraloea orouttll. Allenrolfea oooldentalis 

and Suaeda torreyana appear as a dark band across 

center of photograph.

136

in the present work. Not more than several additional 

137 

speoies, primarily summer-fall ephemerals, may be expected* 

The short distance to the mainland does not seem to 

be an effective barrier to plant migration. Several speoies 

are represented by very small populations consisting of one 

to several individuals* Bursera microphylla. Lopho- 

cereus sohottl. Phaulothamnus splnesoens. and Prosopls 

torrevana. These speoies are precariously established and 

may represent recent introductions* It is also possible 

that they may be relics from deollning populations but 

their distributions are more indicative of relatively 

recent immigration. Lophooereus sohottll. a speoies gener 

ally characteristic of finer textured soils of valley 

plains and bajadas, occurs here only in limited numbers 

near the top of the island, with birds seeming to be the 

agents of dispersal. Prosopls and Bursera occur only near 

the shore and their presence may be attributed to ocean 

currents as well as birds. Chenopodlum murale is abundant 

and well establlsheda and is common even on guano-covered 

slopes. It is indigenous to the Old World (Kearney and 

Peebles, 1951; Wiggins, 196*0 and thus must have reaohed 

the island sinoe its introduction from Europe. The seeds 

are tiny and might easily be wind transported} however, 

the seed is edible and is used for food by the Seri 

Indians. It has also reaohed the remote interior of Isla

Tiburon and is the only vascular land plant recorded from 

the uninhabited guano-covered Isla San Gorge (Johnston, 

1924) in the northern part of the gulf* Therefore I 

believe that bird and/or wind transport are the likely 

agents, with more emphasis on the former. 

The establishment of two forms of Qpuntia fulgida 

(var. fulgida and var. mammlllata) indicate two or more 

independent arrivals to the island. Qpuntia f. fulgida 

ocours primarily on the lower east slopes of the mountain 

138 

while var* mamml11ata is restricted to the sandy flats near 

the east shore. 

All of the species on the island are known from 

nearby mainland regions with the unique exception of the 

prickly pear, Qpuntia of. phaeaoantha. whioh ooours on 

the east-faoing slope of the mountain near peak elevation. 

It is interesting to note that the only other record of a 

platyopuntia (prickly pear) from the islands in the Gulf 

Coast of Sonora is on Isla San Pedro Nolasoo where a dif 

ferent species ooours and is also found only on the east 

side of the island. 

A number of common speoies ooourring on the adja 

cent mainland in seemingly comparable habitats are cons 

picuously absent from Isla Alcatraz. These includei 

Croton califoraloua Frankenla palmerl 

Errazurlzla megacarpa Jatropha""clnerea 

Euphorbia leucophylla Jatropha ouneata 

Euphorbia polyoarpa Larrea alvarloata 

Mammillarla swlnglel

c 

Growth-forms.—Arboresoent species on the island, 

include only Carnegiea glgantea, Qlneya tesota and Pachy- 

oereus prlnglel. Qlneya is represented by a small and 

tenuously established colony on steep slopes in the south- 

central part of the mountain near the summit* Individuals 

do not reach maximum size for the species but may be 

classed as large shrubs. It is here out of its character 

istic habitat and seems to represent fortuitous introduc 

tion by birds* Of the two species of arboresoent oolumnar 

oaotl on the islandv Carnegiea is poorly established while 

139 

Pachyoereus Is one of the more oommon and widespread species. 

Fruiting individuals of Carnegiea are present but most of 

the population consists of the immature individuals. 

Shrubs dominate muoh of the island's vegetation and are 

represented by 15 species, or approximately 40# of the 

flora. 

Suooulents, inoluding cacti and halophytes are 

prominent in the vegetation. These ares 

Abronla maritlma 

Allenrolfea oool'dentalls 

Carnegiea gjgantea 

Lemalreocereus tnurberi 

Lophooereus sohottll 

Qpuntla bigelovll 

Qpuntla fulglda 

Qpuntla of. phaeacantha 

Paohvoereus orIngle1 

Sesuvlum verruoosum 

Suaeda t'orreyana

These species present an evergreen aspect evidencing 

little seasonal variation, while the other perennials 

are, to varying degrees, facultatively drought-deciduous. 

Many of the other species on the island show succulent 

tendencies although they are not classed here as sucou- 

lents. Plants with semi-succulent leaves include Hof- 

melaterla laphamloldes. Lyclum sp., Palafoxla linearis, 

and Phaulothamnus splnescens. An interesting adaptation 

is seen in species with long-persistent leaves which 

become increasingly succulent or semi-suooulent with age, 

£•&•, Lyolum sp., Phaulothamnus splnescens. and Vlscalnoa 

genloulata. 

Ephemerals inolude 13 species, or about one fourth 

of the flora, and are distributed in both the summer-fall 

and winter-spring seasons. These are: 

Amaranthus fimbria tus 



Bouteloua barbate 

Cenchrus palmerl 

ChenopocTlum murale 

Dalea mollis 


Euphorbia petrfna 


Perltyle""emoryj 

Sphaeralcea orouttll 

Trlanthema portulacastrum 

Amaranthus flmbrlatusi Bouteloua barbata. and Trlanthema 

portulaoastrum occur almost exclusively in the summer-fall 

monsoon season; Bouteloua arlstldoldes is primarily a

summer-fall species but sometimes responds feebly again 

with winter-spring rainfall; and the remaining ephemerals 

are non-seasonal. 

Productivity.—Allenrolfea occidentalis and Amar 

anthus watsonll together account for the majority of the 

total number of individual plants, plant cover, and pro 

ductivity (weight of organic matter or total biomass pro 

141 

duced per unit time) on the island. Total weight (standing 

crop) or biomass of Pachycereus pringle1 may equal or 

exceed that of Allenrolfea and/or Amaranthus. but its slow 

growth certainly does not match the annual rate of pro 

ductivity of the latter two. 

It is interesting to note that as a result of very 

different adaptations the ecological and spatial distribu 

tions of Allenrolfea oooldentalls and Amaranthus watsonll 

are essentially mutually exclusive. The former reaches its 

maximum development in the playa region of the island while 

Amaranthus watsonll produces maximum cover during favorable 

seasons on lower slopes and sandy flats. Thus maximum pro 

ductivity appears related to soil moisture but with dif 

ferent local conditions resulting in correspondingly 

different vegetational responses. 

Regions supporting maximum number of species of 

leaf-bearing perennials, higher elevations on the 

east-facing slopes, show only modest plant cover and

IkZ 

therefore relatively low productivity. In contrast Allen* 

rolfea and Amaranthus obtain maximum development in areas 

with relatively few speoles. 

Guano.—•Extensive guano deposits, produced by cor 

morant colonies and other sea birds including pelicans and 

gulls, cover much of the island and impart a white color 

and an unmistakable nitrogenous odor (Figs. 33. 35# and 

36). Guano deposits are least developed on the east side 

of the island and greatest on the north, west, and south 

slopes towards higher elevations. 

It is difficult to separate the effects of aridity 

and guano deposits on the vegetation for the reason that 

the guano deposits occur in regions of extreme aridity. 

It does, however, appear that on Alcatraz the vegetation 

is in part limited by guano deposits. There are no regions 

as large as the western portion of Isla Alcatraz on the 

nearby Islands or mainland which are as barren with two 

notable exceptionsJ dry salt flats (e.g., Playa Noriega) 

and Isla Patos. Guano deposits on Isla Patos likewise 

correspond with extreme aridity. 

Shore,--The east coast of the island is in part a 

sandy beach, and the remainder consists of a more steeply 

rising beach of sand and sea-worn rocks. Hock cliffs and 

bluffs essentially devoid of vegetation form the western 

shores.

Figure 35* Southwest side of Isla Aloatraz* Note thick 

guano deposits and several Paohvoereus pringle1 

at top of mountain.

143

Figure 36. Cormorant rookery on northeast-faolng slope on 

east side of mountain, Isla Alcatraz, at ca. 

135 m, elevation. Vlscalnoa genloulata (middle 

foreground) and Nlootlana trlgonouhylla (left 

of Vlscalnoa and extreme foreground)•

4< v< 

'J,**-, * > 

144

The first plants encountered on the sandy beach 

above the high tide zone are low, spreading, and suooulent 

perennials and one saltgrasss Abronia marltlma. Atrlplex 

1^5 

barolayana. Sesuvlum verruooaum. and Sporobolus virgin!oua> 

Playa.—A small landlocked saline playa or flat 

ooours on the low eastern portion of the island. It sup 

ports a dense growth of halophytio perennialst Allenrolfea 

oooldentalls. Cressa truxlllensls. Monanthoohloe llttoralls. 

and Sesuvium verrucosum. This community shows little sea 

sonal variation due to what is undoubtedly a more perennial 

source of ground water than obtains in the adjacent and 

higher ground. 

Allenrolfea oooldentalls dominates the playa region, 

produoing 90-100# cover on the lowest and wettest ground and 

gradually diminishes in density onto higher and seemingly 

less saline but dryer terrain. The other speoies present 

are inoonsplouous in comparison and oeour on less than $% 

of the area oovered by Allenrolfea. 

Several halophytes common to nearby mainland 

regions are conspicuously absent» £•&•» Batls marltlma. 

Maytenus phyllantholdes. and Sallcomia paclflca. These 

species ooour on low saline soils which are not out off 

from the sea, and with relatively well drained soils. In 

suoh places Allenrolfea oharaoteristloally oooupies a 

position on higher and dryer ground than the above mentioned

species. The few other halophyte species found together 

with Allenrolfea on Aloatraz occur only In the lowest and 

wettest portion on the playa, corresponding to their 

characteristic position in other nearby regions* 

li*6 

Flats .—Vegetation on the higher ground of the flat 

eastern portion of the island consists primarily of sparsely 

distributed but aggregated desert shrubs and seasonally 

dense stands of ephemerals. These aret 

Allenrolfea occldentalls Datura dlsoolor 

Amaranthus flmbrlatua Euphorbia petrlna 

Amaranthus watsonlT Lyclum BP. 

Atriplex barolayana Qpuntla*rulglda mammlllata 

Bouteloua arlstldoldes Paohycereus prlnalel 

Bouteloua barbata Palafoxla linearis 

Bursera mlcrophvlla Perltyle"""smoryl 

Carneglea glaantea Proaopls torreyana 

Cenchrus""palmerf""" Suaeda torreyana 

Chenopocflum murale Trlanthema portulaoastrum 

Dalea mollis VIsoalnoa*"genl culata 

In February 1965 the total plant cover amounted to approxi 

mately 65/6* The following 12 species were present in an 

area not more than 50 m. across (Fig. 3*0« 


iH^rlPlex uarclayana 


Cenohrus"*palmerl 

ChenopoJlum murale 

Datura dlsoolor 

Euphorbia petrlna 

Lyclum BP. 

Qpuntla fulglda mammlllata 


Sphaerafoea orouttll 


The majority of plant cover at this time was produced by 

three ephemeralss Amaranthus watsonll. Palafoxla linearis.

and SPhaeraloea orouttll* On December 2 of the same year 

the ephemeral8 had largely disappeared and total plant 

coverage was only 3 

Slopes.—Perennial vegetation on the lower east 

slopes of the mountain Is comprised of widely spaoed 

1*J7 

medium-sized desert shrubs, e.g., Allenrolfea oooldentalls. 

Lyolum sp., Qpuntla fulglda var. fulalda. Suaeda torreyana. 

and Vlsoalnoa geniculate. Allenrolfea and Suaeda extend 

only onto the lowermost part of the bajada slope and reaoh 

greater development on the adjacent saline flat* Following 

favorable seasons these slopes support extensive stands of 

Amaranthus watsonll whloh reaoh 80 to $0% ooverage or more 

and from a distance give a grassy appearance to the Island. 

Perennial coverage amounts to less than $%• 

Arroyo or semi-riparian vegetation is lacking but 

a series of short and generally unbranched arroyos or 

gullies on the lower east slopes support a slightly 

greater number of species and shrubs than adjacent areas* 

Lyolum and Vlsoalnoa are common along these gullies and 

Phaulothamnus. which Is rare on the Island, Is present* 

Paohycereus Is common on the nearly straight and rooky 

ridges but absent from the Intervening gullies* These 

ridges seem to represent an older surface now dlsseoted 

away In the region of the gullies* Judging from the size 

of the cacti, the erosion time appears to be several 

deoades or more.

Near the reoess at the base of the mountain there 

is a looalized area in whioh Paohyoereus pringlei and 

Qpuntia fulgida var. fulglda are so dense that other 

plants are virtually excluded. Fallen Joints of Qpuntia 

IkQ 

cover the ground, and readily take root forming new plants* 

At higher elevations on the east side of the mount 

ain are populations of speoies whioh are not found else 

where on the islandi e.g., Beloperone oallfomloa. Hof- 

melsteria laphamioldes, Lophooereus schotti. Olneya tesota. 

and Qpuntia of. phaeaoantha. These speoies generally ooour 

on northeast exposures. In addition to the above speoies 

Niootiana trigonophylla and Vlsoainoa genloulata locally 

reaoh maximum development. 

The north side of the mountain is buffeted by 

strong winds and vegetation is relatively depauperate. 

The shallow and loose soil affords poor holdfast for roots, 

the slopes are steep, and the guano deposits are thiok. 

Nine speoies of plants are present but all attain greater 

development elsewhere on the island. These speoies are* 


Atrl pleaHBar olayana 

Carneglea gjganrea 

Chenopodium murale 

Lemaireooereus thurberi 

Lyoium BP. 

Qpuntia plgeloyil 

Paohyoereus pringlei 

Vlsoainoa genloulata 

The oaotl are rare and are small individuals only, prob 

ably waifs from nearby areas.

The steep and rooky western part of the island is 

inhabited by great numbers of sea birds, particularly cor 

morants » gullsa pelloans, and frigate birdst and the 

resulting guano deposits are thlok. This part of the 

island is largely devoid of vegetation (Figs. 33 and 35)* 

149 

Paohvcereus pringle1 is the only widespread perennial; how 

ever, its density is low, producing much less than 1% cover. 

A single ephemeral speoies, Amaranthus watsonll. is also 

sparse but may produoe up to 5% oover in small localized 

areas. No other plants were found in this strange guano- 

covered landscape, although a few extend from the adjacent 

east slopes to the top of the island. 

Summary*--The vegetation of Isla Aloatraz is xero- 

phytio desertscrub. Speoies of Amaranthaoeae, Caotaoeae, 

and Chenopodiaoeae form the most widespread and dominant 

elements. Several speoies ooour only in small looalized 

populations of apparently non-reproducing individuals. 

These are Interpreted as reoent arrivals to the island. 

Aridity and guano deposits render much of the island, 

especially the western part, inhospitable to the develop 

ment of vegetation. However, closeness to the mainland 

and a relative high degree of habitat diversity allows a 

comparatively high number of speoies to exist in the 

remaining portion. Two speoies of lizards are the only 

terrestrial vertebrates. There are no endemios.

ISLA SAN PEDRO MARTIR 

15° 

Isla San Pedro Martir, lying in deep water in mid- 

gulf, is the most isolated island in the Gulf of California* 

It seems to be volcanic in origin and has probably never 

been oonneoted to any other landmass. The shore rises 

abruptly to high sea oliffs which cure olaimed by thousands 

of noisy birds. There are no beaohest alluvial deposits 

or outwashes, and consequently there is no development of 

shore vegetation* Tamayo (19^9* P« 581) states that the 

island forms an equilateral triangle with sides 1.2 kms. 

long which would give an area of 0*62 sq. kms. However* 

I believe that the island is closer to 1.0 sq. Ion* in size. 

Above the high sea oliffs the topography shows relatively 

little relief and oonslsts roughly of two main plateaus 

or mesas, one at about half way and the other at the top 

and oocupying the eastern half of the island and with a 

peak elevation of 320 m. (Tamayo, 19^+9 )• 

Riparian or semi-riparian canyons and arroyos are 

absent. Most of the surface of the island is exposed and 

offers little or no shelter from wind. Soil is poorly 

developed and shallow. The island is covered with a rook 

surface of varying size and of voloanio origin. At its 

west end a rock headland about 75 to 100 m. high juts out 

into the sea and is oonneoted to the rest of the island by

a lowsaddle. The only landfall, although a poor one and 

oooupled by sea lions, is to the north of this headland. 

In the saddle are the ruins of rook-walled shelters built 

by guano workers. The occupation was not lengthy and the 

151 

island has long sinoe been uninhabited. There is no source 

of fresh water. The area whioh was mined and where the 

workers lived is mostly below the vegetated part and other 

wise there is no evidence of man-influenced disturbance of 

the biota. 

There are no meteorological reoords for the island 

but the climate is certainly arid with hot summer days and 

moderate winter nights. Winter rainfall ocours* as dearly 

evidenoed by the species of ephemerals and the general ver 

dant condition of the vegetation in late January of 19&3* 

In the early mornings in late January all but the lowermost 

portion of the island was enveloped by fog which remained 

until about an hour or so after dawn (Fig. 37) • The vege 

tation was thoroughly wet from this pre-dawn fog which 

evidently provides an important source of moisture. 

Extensive guano deposits on the steep sea cliffs 

and lower elevations (Pig. 38) further indicate arid con 

ditions. The midday temperature in late January of 19^3 

was surprisingly warm and slightly uncomfortable. 

Terrestrial vertebrate fauna includes a rattle 

snake, Crotalus atrox. and two small endemic lizards*

Figure 37* Southeast side of Isla San Pedro Martir, 

shortly after dawn, January 1963*

152

Figure 38. Northwest side of Isla San Pedro Martir, 

approximately 100-120 m. elevation. Paohy- 

oereus prlnglel and Sphaeraloea halnsiana.

153

Cnemldophorua tlgrla martyrla and uta palaerl. in addi 

tions Phyllodaotyllus might reasonably be expected to 

ocour. No native land mammals are known* 

For Ita size and elevation the vegetation and 

flora of San Pedro Martlr la the most Impoverished of any 

of the Sonoran Islands. Twenty-five speoles of vascular 

land plants are known and It Is predicted that further 

Investigation will yield no more than 5 to 10 additional 

ones. Distance to neighboring land masses, aridity, and 

relatively low ecologlc diversity all seem to contribute 

to the paucity of speoles. Unlike the reptilian fauna 

15^ 

there are no known endemlo plants on Isla San Pedro Martlr. 

Two prlnolpal phytogeographlo patterns are evident 

among the floras (1) speoles common to both sides of the 

Gulf, and (2) plants ooourrlng otherwise only on the Baja 

California side of the Gulf. Most of the speoles show the 

former pattern and for these oolonlzatlon could have ori 

ginated from either side of the Gulf or from other Islands. 

The seoond pattern Is shown by only a few speoles, £,•£•» 

Pelucha trlflda and Sphaeralcea halnesll. Camlssonla 

oardlouhylla shows a relationship with Baja California 

and the west coast of Tlburon. It ooours on the mainland 

of Sonora only at the head of the Gulf. 

Significantly the plants found on fttertir are small- 

seeded or with dlssemlnules adapted to over-water

colonization. The fruits of Vaseyanthus InsularIs are 

light structures with alr-fllled chambers readily suited 

to ocean dissemination (see Gentryt 1950)* The sticky 

fruit of Mentzella adhaerans might readily be carried to 

the island on the feet of birds while others such as Flcus 

palmer1. Paohycereus pringlel. and Stegnosperma hallml- 

follum have edible fruit and may also have been introduced 

by birds. Light weight achenes of the composites oould 

easily be wind transported from neighboring land masses. 

It is Interesting to note the relatively large representa 

tion of this family on the island, l*e.f 7 species or 

nearly 25% of the flora. 

The vegetation is sparse throughout and the major 

perennials are generally widely spaced. The guano-covered 

cliffs and lower slopes at the edge of the island are 

nearly devoid of plants. On ascending the island from its 

only apparent point of ingress at the west end, one is 

Impressed by the strangeness of the pioneer community con 

155 

sisting of three species of divergent growth-formst Paohy 

oereus pringle1. Snhaeralcea hainesli, and Vaseyanthus 

lnsularls. These species are concentrated along drainage- 

ways as they extend below the more vegetated plateau (Fig. 

38). The same speoles dominate muoh of the remaining land 

scape. Many of the other perennials are localized or rare. 

The number of species and population densities are greatest

towards the top of the island and gradually diminish at 

lower elevations. Among the plants oonfined to the higher 

elevations are Baooharis sarathroides. Fieus palmer!. 

Peluoha trifIda, and Viscalnoa geniculate. 

Major perennials consist of aphyllous stem succu 

lents (cacti) and drought-deolduous shrubs. Species show 

ing extensive stem die-back during dry season are common, 

£•£• • Abut lion palmerl. Nlootlana trlgonophylla. Sphaeral- 

cea hainesli. and Vasevanthus insularis. and to a lesser 

extent Fioua palmerl shows a similar habitat. Vasevanthus 

insularis with its long trailing stems is the only speoies 

present which may be considered to be vining. Several 

156 

growth-forms common on the opposite shores are conspicuously 

absent on Martir, e.g., leaf-bearing trees and leaf succu 

lents. Also absent are plants with bulbs, stolons, rhi 

zomes* or tuberous roots. Winter-spring ephemerals com 

prise about 30% of the flora, the commonest of which 

include Aristlda adscensclonls. Euphorbia petrlna. Ment- 

zella adhaerans. and Peritvle californica. The nature of 

the summer-fall flora is unknownj however, most of the 

winter-spring ephemerals are species potentially capable 

of growth again during the summer-fall rains. 

Siy0g£ê—Aridity and relatively little habitat 

diversity appear to be principal factors contributing to 

the relatively depauperate condition of the flora and

fauna of Isla San Pedro Martlr. Insular isolation, how* 

ever, is here inseparable from aridity. Two endemic 

lizards are present but endemics do not ocour among the 

plant species. Two prinoipal phytogeographic patterns are 

showns (1) species common to both sides of the Gulf, and 

157 

(2) species with distributions largely in the arid northern 

part of the Gulf. Species of the latter group oocur on the 

opposite Gulf Coast of Baja California, the adjacent penin- 

"Hsular 

islands, and the west side of Isla Tiburon, but are 

absent from the Sonoran coast south of the Infernillo.

ISLA TIBURON 

Isla T1buron Is the largest island in Mexioo. Its 

geology, topography, and vegetation are complex. Gentry 

(19^9» P* 9*0 provides the following sketch of the islands 

It is separated from the Sonoran mainland by a 

shallow narrow channel, "el infiernillo," two to 

five kilometers wide and only three to four meters 

deep. Roughly quadrangular in shape, the island 

contains about 1170 square kilometers. Although 

mountainous, there are extensive valleys • • • • 

There are two igneous ranges of mountains trending 

north and south and paralleling the adjacent ranges 

of Sonora. The western is Sierro Henor, the eastern 

and higher is Sierra Kunkaak . • • with a middle 

peak elevation of 1218 meters ... the shallow 

infiemillo ohannel was emerged repeatedly during 

the low sea levels of the glacial periods. 

158 

The geology is briefly discussed by Anderson (1950). 

The Inferoillo* earned its name from its treacherous cur 

rents and dangerously shallowsand bars; it is navigable 

only by the smallest of craft (U.S.N. Ocean. Office, 1953-)* 

At low tide large sand bars become exposed, even in mid- 

channel, and at the Santa Rosa narrows tide-exposed sand 

flats may extend out into the sea two to three kilometers 

in a southerly direotion. It has been rumored that at 

lowest tide a horse can wade aoross the channel except for 

a very short distance which might be traversed by swimming. 

Such a feat, however, is unlikely, because of the strong 

1. Infemillo is a local usage and corruption of 

the word " Infiemillo."

currents which are present exoept during the few minutes 

of neap tide. Thus the island is today out off to immigra 

tion of terrestrial life exoept by overwater means* It is 

reasonable* however• to suggest that the narrow Infernillo 

does not effectively Isolate the flora* 

Indians (Griffen, 1959t MoGee, I8961 MoGee and Johnston, 

1898» Kroeber, 19311 Moser and Moser, 1963)* who refer to 

themselves as the Kunkaak (see Noser, 1961)1 it is the set 

ting of many false and exaggerated tales* The number of 

seri living on the island has greatly dwindled in recent 

years and today it is essentially unoccupied* 

tlally not different from the adjacent Sorioran mainland* 

Twenty-five species of reptiles and 2 speoles of amphibians 

are now known to occur on the island (Appendix B)« The 

mammalian fauna is likewise similar to the adjacent main 

land but some endemic forms have apparently evolved on the 

island (Appendix C), Critical study of the mammalian 

fauna may show that some of these endemic taxa are not 

dlstinot from mainland populations. More striking are 

species of larger mammals which occur on the adjacent 

mainland and are consplouous by their absence on Tiburon* 

These include: 

The island is the traditional home of the Seri 

Fauna.—The herpetofauna of Isla Tiburon is essen< 

Fells ooncolor Ovls canadensis 

Lepus californlous Peoarl"~angulatus 

Lvnx rufus Prooyon lotor 

oousl 

Sylyllagus audubonl 

Taxldea taxus

Antllocapra amerloana onoe ranged aoross northern Sonora 

Including the coast opposite Isla Tiburon (Burt, 1938) 

but it apparently did not ooour on Tlburon, at least in 

modern times. The total lack of cats also seems unusual. 

It may be that some of these species, and others» used to 

i6o 

oocur on the island but the hunting pressure by indigenous 

people caused their local extinction. The relatively few 

watering plaoes on the island would attract larger animals 

and provide an easy means of hunting. Although such may 

be the case for some species it seems that the land mass 

of the island is not sufficient to support many species 

of larger mammals. The following speoies are especially 

abundant on the islands Canls latrans. Dipodornvs merrlami, 

Lepus allenl. Neotama albigula. and Odocolleus hemionus. 

Vegetation.--The vegetation of Isla Tiburon 

includes mangroves along the eastern shore, subtropical 

scrub on Sierra Kunkaak, and desertsorub oovering most of 

the island. The different communities or vegetation types 

on the island broadly intergrade with each other in a con 

tinuum pattern. The most prominent of these inolude: 

Littoral scrub 

mangrove 

halophytic succulents and salt grass 

Desertsorub 

coast shrub (Frarikenla palmerl)

oreosotebush (Larrea dlvarloata) 

mixed desert shrubs 

columnar cacti and mixed small desert trees 

and shrubs 

semi-riparian desert shrubs and trees 

riparian (aguajes or tlnajas) 

Subtropical scrub 

riparian or semi-riparian 

thomsorub of higher elevation (Lyslloma 

dlvarloata and Aoaola wlllardlana) 

Much of the coast supports shore vegetation which 

l6l 

is substantially similar to the mainland* Marshy areas are 

characterized by perennial evergreen sucoulents and salt 

grasses. The most extensive development of littoral sorub 

ocours along the Infernlllo in shallow sea-water inlets 

and on gradually sloping beaohes. The rugged and exposed 

west and south coasts support meager shore-plant communi 

ties and where sea cliffs plunge directly into the ooean 

shore plants are precluded altogether. Common shore 

species are listed below in the approximate order in which 

they are often enoountered from lowest to higher elevations 

Avlcennla «ermlnans Allenrolfea oocldentails 

suaeaa torreyana 

Vasevanthus InsularIs 

Atrlplex barolayana 

Sesuvlum yerrucosum Frankenfa palmerT palmerl 

Monanthochloe llttoralls Atrlnlex*"linearis

There are two relatively small but well developed 

162 

mangrove esteros on the Island, both along the Infernillo, 

one at Santa Rosa and the other at Palo Fierro. The vege 

tation appears substantially similar it both and is des 

cribed for Palo Fierro (pp. 184-186), 

Large areas of the Infernillo shore are bordered 

directly by impenetrable thickets of Mavtenus phyllan- 

tholdes. In suoh places the shore gradually slopes into 

the sea and the soil is muddy and permanently moist rather 

than sandy and subject to periodic drying. Although Mav- 

tenus sometimes extends a short distanoe inland onto desert- 

dry soils it reaches maximum density and height along muddy 

shores bordering mangroves. In auoh oases it often forms 

pure stands with 100% coverage and may reaoh heights of 

3 to 4 m.f or rarely 5 

The coast shrub or Frankenla palmer1 zone is well 

developed on Tlburon but it is not found on the other 

Sonoran islands. It oooupies an often well-defined zone 

near the shore Intermediate between the halophytic shore 

scrub and the more extensive mixed desert shrub communi 

ties. 

Throughout its range on Tlburon* Frankenla occurs 

only on sites direotly facing the sea. On hills bordering 

the shore it does not extend inland beyond the seaward 

slopes, but on low terrain, suoh as gradually sloping

ajadas, It ranges inland to about one kilometer. Con 

densation of dew on oool nights dampens the foliage, and 

at dawn moisture may be seen dripping off the wet leaves. 

The distribution of Frankenla thus appears to be limited 

163 

by maritime dew more than any other faotor. Soil and topo 

graphy within the Frankenla zone are highly varied and 

include rocky hills and pediments* bajadas, sandy flats, 

and coastal dunes* Arroyos dissecting and interdlgitatlng 

with Frankenla flats or pediments contain "gallery" com 

munities of mixed desert shrubs. Unlike the protected 

arroyos, the ooast shrub communities are invariably exposed 

to the full force of winds whloh place severe limitations 

on moisture. The overall harsh conditions to whioh the 

Frankenla sorub is exposed is reflected by the paucity of 

species, ooverage, and greatly reduced stature of the 

plants and their xerophytlc adaptations. EphemeraIs may 

be present but they are sparse and show marked increase 

toward the upper (inland) limits of the coast-shrub zone 

as it merges with the mixed desert shrub communities of 

bajadas and hills. 

On iBla Tlburon the coast-shrub or Frankenla zone 

is most evident along the Infernillo and it becomes greatly 

narrowed on the other more rugged coasts. It is absent 

from sea-cliff shores at the south and west side of the 

island.

At the coastal margin of the coast shrub zone 

there are few speciest although growth-forms may be rela 

161* 

tively diverse, £,•£•• leaf and stem succulents* halophytes, 

and evergreen and drought-deciduous speoles may be present. 

The major portion of the Island Is covered with a 

shrubby to semi-arborescent desertscrub of diverse types. 

Vegetation along arroyos or washes Is arborescent or semi- 

arborescent. Away from streamways In the more arid regions 

there are broad stretohes of creosotebush scrub (Larrea 

dlvarlcata). 

Extensive stands of tree or giant cacti are absent 

over most of the Island and were found only along the east 

side of the central or Interior valley which drains Into 

Bah£a Agua Dulce. Here the bajada slopes gradually west 

ward and supports a large population of Cameglea gjgantea 

(saguaro), small desert trees, £•£•* Gercldlum mlcrophyllum. 

and mixed desert shrubs. The exposure slope compares with 

the bajada of the mainland side of the Infernlllo where 

extensive stands of Pachycereus prlnglel (cardon) occur. 

The Inland position on Tlburon seems to favor the saguaro 

instead of the cardon. The relatively sparse populations 

of cardon therefore seems to be due to the absence of west- 

facing coastal bajadas. Cardon is widely scattered on the 

island and the colonies are generally looalized.

On Sierra Kunkaak rich desertscrub gradually 

merges into thornscrub. The disoovery of an extensive 

region of subtroploal sorub in the interior oanyons and 

165 

higher elevations raises many new and interesting problems* 

Phytogeography«—Two hundred and sixty speoles of 

plants are reoorded in the present work (Appendix A) from 

Isla Tiburon and it is reasonable to expect another 25% 

to be present. Most of the additional species will prob 

ably come from the higher elevations of Sierra Kunkaak 

whioh are still nearly unknown biologically. The array 

of plant taxafound on the island is "well balanced" and 

indicative of a continental region rather than an island. 

An undesoribed speoies of Schlnocereus belonging to the 

peotinatus complex is the only endemic plant on the island. 

(Ferrooactus wlsllzenll var. tlburonensls. which is a 

scarcely differentiated ecotype, also oocurs on the adjac 

ent Sonoran mainland.) 

Most of the species occurring on Tiburon are found 

on the adjacent mainland; however, the exceptions provide 

interesting phytogeographlc information. A small number 

of speoies are common to Baja California, its adjacent 

islands, and Isla Tiburon but do not occur on the Sonoran 

mainland, e.g., Acalypha commonduana. Cassia confinis, 

Castela sp.» Cryptantha fastlglata. Drymarla halosteoldes. 

and Fagonla palmerl. An interesting pattern is seen in

several species which ooour at the head of the Gulf and 

the arid northern portion of Baja California but which are 

not present on the mainland of Sonora as far south as the 

166 

latitude of Tlburon, e.£., Camlssonla cardlophylla. Fagonla 

pachyaoantha. Franserla lllclfolla. Lotus salsuglnosus. and 

Oenothera leptocarpa. on Tlburon these speoles seem to be 

restricted to the arid western part of the Island. The 

Interior regions of Sierra Kunkaak support a number of 

species with subtropical or southern affinities which are 

not found along the Gulf coast north of the Guaymas region, 

although some range northward along the eastern edge of 

the desert. These lnolude: 

Ayenla glabra 


Croton nuagdalenae 

Gualaoum ooulterl 

Laslaols aorgholaea 

Lyslloma* dlvarloata 

Toume/ortla hartweglana 

Growth-forms. —The broad span of growth-forms present 

on the Island nearly equals the Guaymas region In richness. 

Large trees are present but not common In the Interior of 

the Island. The tallest and most massive tree Is Flcus 

palmerl whloh often reaches 10 m. In height and exceptional 

specimens reaching oa. 25 m. have been discovered In the 

Interior. The second tallest tree Is Bumella occidental!s 

whloh occasionally reaohes 12 m. but smaller specimens are 

more numerous. Other trees found are listed below In

approximate decreasing order of maximum heighti 

Prosopls torreyana 

Olneya tesota 

Aoaola wlllardiana 

Condalla globosa 

Jaoaulnla pungens 

Ceroldlum florldum 

LyBlloma""dlyarlcata 

Ceroldlum mlcrophyllam 

Koebcrllnla splnosa 

Buraera mlorophyllum 

167 

Tree oaoti are represented by Carneglea gjgantea and Paohv- 

cereus prlnglel. and semi-arboresoent speoies are Lemalreo- 

oereus thurberl« Lophooereus sohottll. Maohaereooereus 

gummosus. and Qpuntia fulglda. Platyopuntia (Qpuntia) or 

priokly pear is conspicuously absent. 

Shrubs and sub-shrubs or suffrutesoent plants are 

the most abundant forms. The ubiquitous drought-deciduous 

desert shrub ooours nearly throughout the island and forms 

the most important element in the landscape. Simple-leaved 

speoies are often the most numerous although pinnate-oom- 

pound groups are prevalent) e.g., Bursera mlorophylla and 

the legumes. 

A single fern, Notholaena oallfornloa. has been 

collected only in the vicinity of Sauzal and Teoomate 

above 200 m. elevation and is rare. Other ferns may be 

expected on Sierra Kunkaak• 

Only a few oonspiouous perennial vines have been 

found on Tiburon, e» Cardlospermum oorlndum. Janusla 

oallfornloa, Janusla graollls. and MargAenla fldulla.

Ephemeral vines are likewise few, e.£.» Cusouta SPP. and 

Phaseolus filiformIs. Other vining speoles are unoommon 

or only weakly vining. The latter are interesting because 

they are generally derived from subtropical forms of 

168 

strongly vining habit, e.g., Jaoauemontla abutlloldes east- 

wood lana. Masoagnla maorootera (the Tiburon plants are 

soarcely vining), Passlflora foetlda gossyplfolla. and 

Tragla amblyodonta. 

There are only two species of root perennials on 

Tiburonj Amoreuxla palmatlflda and Probosoldea althel- 

folia. Both have a large fleshy underground tuber and 

respond to the summer-fall season. Other geophytes are 

unknown here. 

The ephemeral flora of Isla Tiburon is now rela 

tively well known except for the higher elevations of 

Sierra Kunkaak and oonsists of approximately 72 speoles 

or nearly 28# of the total flora. Twenty-two of these 

species are characteristically restricted to the summer- 

fall rainy season, 25 ocour almost exclusively with winter- 

spring precipitation, and the remaining 26 are non-seasonal 

(ooourrlng during both seasons). The distinction between 

summer-fall and winter-spring speoles is not always exaot, 

e.£., certain summer-fall species may sometimes respond 

weakly to winter-spring rainfall and vice versa. In the 

following list of ephemerals the summer-fall speoles are

lndloated with an S, winter-spring species are indicated 

with a W, and non-seasonal speoies are unmarked. 

169 

Aohyronyohla oooperl (W) E* polyoarpa 

Alllona lnoaraata cs) 1. setlloba 

Amarantnus flmbrlatus (S) Kallstroemla oallfornioa (S) 

Amarantnus wataonll (S) K. firand^flora CS? 

Andraohneolllato- Llnarla oandensls texana (W) 

glonduJLosa CW) Lotus tomentellus JW) 

Antirrhinum oyathiferum L. salsuglnosus TW) 

A. 1?atsonll (VP Eupinug arlzonloa (W) 

Aristlda adsoenslonis Mentzella adhaerans 

Boerhaarla oouitert CS) M. hirauTlssima CW) 

B« ereota (S) Mollugo oervlana 

Bouteloua arlstldoldes (S) Nama of. hlspldum (W) 

B. J barbaEa CS) Nlootlana oleyelandll (W) 

aoftvga eardlophyllatW) Oenothera leptooarpa (W) 

the length of the west ooast. The divide is close to the 

shore and in some plaoes it drops away into sheer sea 

oliffs* In the vicinity of Ensenada Blanoa it is set 

hack from the shore several kilometers* The terrain is 

rough and rises steeply with several discernible terraces* 

In general the vegetation is sparser and more xerophytic 

in the north coastal margin of Sierra Henor than toward 

the south where it appears to be slightly less arid* How 

ever* the entire west coast is more arid than the rest of 

the island* 

Ensenada Blanoa is the name given by fishermen to 

an area long the southwest ooast approximately 15 to 20 

kms* north of Punta de Willard* It is sometimes also 

referred to as El Vaporeto. Many of the mountains and 

hills in the region form flat mesas at their summits and 

are interspersed with broad rooky oanyons or narrow valleys 

running perpendicular to the ooast. 

The vegetation at Ensenada Blanoa is sparse and 

mostly dominated by small to medium-sized desert shrubs 

with relatively small leaves* Trees are generally absent* 

Coast Shrub Zone (Frankenla)*—High beaches of 

cobblestone-like rock preclude most development of lit 

toral scrub although a few halophytio species often occur 

scattered along the inland edge of the rock beaches, £•&•» 

Atrlplex polyoarpa and Suaeda torreyana*

The low gravelly and stony pediments between the 

beach and the first hills are covered with nearly pure 

stands of Frankenla palmerl» Atrlplex barolavana often 

follows small gullies transversing the pediment* The 

coastal pediment here is narrow and seldom exceeds 100 to 

300 m. in width. 

171 

Frankenla continues onto rocky slopes bordering the 

pediment and faoing the sea (Plot 25# Table 25)• Here 

dwarf shrubs and suffrutescent species constitute the 

dominants, e.g., Atrlplex barclayana and Frankenla palmerl. 

Host of the other small desert bushes and herbaceous plants 

recorded in Plot 25 ocour along small but steep rocky 

gullies* The total plant coverage is 12% and Frankenla 

alone accounts for 10% coverage. The plant coverage is 

looally highest along the edge of gullies and toward north- 

oriented portions of the slope. Twenty-six speoles were 

found in the quadrat and 28 in the stand. More than half 

of the species present are ephemerals or herbaceous. 

Mesas.—Mesa-like ridge-crests with desert pavement 

at Ensenada Blanca are partially barren and support only a 

sparse cover of xerophytic desertsorub (Plot 26, Table 26, 

Fig. 39). Winds are persistent and the desiocatlng effects 

and lack of runoff of water from adjacent areas correspond 

with the poverty of vegetation. Large areas are devoid of 

plants and maximum coverage reaches only 5»5%» Most of the

TABLE 25 

172 

PLOT 25- ENSENADA BLANCA, ISLA TIBURON, CA. 100 M. INLAND 

(EAST) PROM SHORE, CA. 15-20 M. ELEV. ROCKY HILLSIDE PACING 

SEA, WEST EXPOSURE, 295°» SLOPE 32)*. 29 JANUARY 1965 

Maximum Mean % 

Number height height Coyer- 

Speoles (0*1 ha) age 

Lyolum sp. 

Solarium hlndslanum 

Frankenla palmerl 


Franserla dumosa 

Hibiscus denudatus 



D1tails lanoeolata 

Mammlllarla sp. 

Total 


3 

5 

252 

1 

k 

11 

2 

570 

2 

8*17 


Boerhaavla of. ereota 



Cenohrus palmerl 

Dalea mollis 

D1taxis neomexloana 

Drymarla halosteoldes 

Euphorbia erlantha 



Fagonia paohyaoantha (seedling and small plants) 

Panloum arlzonloum 

Perltyle oallfomloa 

Perltyle emoryl 

Physalls sp. (annual) 

Trlanthema portulaoastriun 



10 

0.5 

1.5 

12

TABLE 26 

173 

PLOT 26. ENSENADA BLANCA, ISLA TIBURON, CA. 150 M. INLAND 

(EAST) FROM SHORE, CA. 22 M. ELEV. MESA-LIKE RIDGE-CREST. 

2? JANUARY 1965 


Number height height Cover 

Speoies (0.1 ha) (ft) (ft) age 

Maohaerooereus gummosus - 6.2 

Fouquleria splendenB 1 5.2 3.1 

Errazurizia megaoarpa 1 2.4 - 0*5 

Hibisous denudatus 3 1*5 1*3 

Atriplex barolayana 271 1.1 0.9 4*0 

Jatropha ouneata - 1.0 

Enoelia farinosa lit 0.6 - 1.0 

Fagonla paohyaoantha 174 0.4 0.2 - 

Total 464 5*5 



Boerhaavia of. ereota 

Drymaria halostoold.es 

Euphorbia of. mloromera 

Fagonla paohyaoantha (seedlings andanall plants) 

Kallstroemla grandiflora 



Trlanthema portulaoastrum 


Total speoies in stand: 17

Figure 39. Ensenada Blanoa, Isla Tlburon. Partially 

barren mesa with Fagonla paohyaoantha and 

a few soattered AtrlPlex barolayana. Fou- 

aulerla splendens In baokground*

174

plants present are aggregated in the shelter of large 

rooks or in slight depressions where Hater may gather fol 

lowing rainfall. Speoles ooourring here generally reach 

greater development in adjacent or nearby habitats and 

appear to be stragglers., on the mesa-top* A triplex bar- 

olayana is common but dwarfed. Fagonla pachyaoantha is 

175 

the only speoles reaching maximum density but the perennial 

individuals are for the most part restricted to sheltered 

niches and shallow gullies or depressions. Its nearly 

prostrate habit appears well adapted to the wind-buffeted 

mesa. Both Fagonla and Atrlplex may flower in their first 

year or season of growth and the gap between annual and 

perennial habit is not sharp. Ephemerals outnumber the 

perennials in number of species, but they are scarce. Like 

the perennials they ocour aggregated at the base of shrubs 

or in the shelter of rooks or shallow gullies. 

Canyons.—Small intermont valleys or broad canyons 

support rioher desertscrub than the adjacent slopes. How 

ever, desertsorub here is relatively xerophytlc as com 

pared with other regions of the island. Mixed desert 

shrubs and ephemerals form the major elements of the can- 

yon-bottom community (Plot 27» Table 27). The streamways 

are not stable and their shifting courses, probably altered 

by flash floods, produce locally barren areas of sand and 

gravel* The western margin of the island may be the only

TABLE 27 

176 

PLOT 2?. ENSENADA BLANCA, ISLA TIBURON, CA. 1/2 KM. INLAND 

(EAST) FROM SHORE, CA. 6 M. ELEV. MBROW FLOODPLAIN IN BROAD 

CANYON. ROCK, GRAVEL, AND SAND SOIL. 30 JANUARY 1965 

Species 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

" f. 

Cover 

age 

Fouquieria splendens 1 10.8 - 0.5 

Atamisquea emarginata 1 5.8 4.4 0.5 

Lyoium sp. 1 5.* - 0.5 

3tegnosperma halimifolium - 5.* - 

Simmondsia ohinensis 2 4.8 4.4 0.5 

Lyoium sp. 6 4.4 4.3 0.5 

Sphaeraloea sp. 11 4.2 3.9 - 

Colubrina glabra 2 3.8 - 0.5 

Condalia lyoioides 3 3.7 3.0 - 

Larrea divarioata 4 3.5 - 0.5 

Bursera hindsiana 1 3-0 - - 

Errazurizia megaoarpa 23 2.9 2.0 0.5 

Enoelia farinoaa 6 2.6 2.1 1.5 

Jatropha ouneata 1 2.6 - - 

Franseria divarioata - 2.2 2.1 - 

Eriogonum inflatum 12 2.1 - - 

Ferrooaetus Kislizenii 1 2.0 - m 

Hoffmanseggia lntricata 19 1.7 1.3 - 

Atriplex barolayana 764 1.6 1.1 8.0 

Ditaxis lanoeolata 2 1.2 1.3 - 

Fagonia pachyacantha 30 1.2 0.7 - 

Condalia globosa 1 1.1 - 

Hibiscus denudatus 1 1.0 - - 

Opuntia fulgida «• 1.0 - " 

Total 901 13*5


TABLE 27 —CONTINUED 

Antirrhinun oyathiferum 

Aristida adsoensionls 

Boerhaavia of* ereota 

Bouteloua aristidoides 

Coreooarpus of. arlzonlous 

Ditaxia neomezloana 

Euphorbia of* mloromera 

Euphorbia pediculifera 


Mentzelia adhaerans 

Phaseolus f11iforals 

Trianthema portulaoastrum 




part where flash floods are a major faotor because of the 

partly barren and steep slopes of the Sierra Menor range. 

Thirty-three speoles are recorded in the quadrat and 37 in 

the stand* Perennials exceed ephemerals In number of 

species yet the total number of ephemeral speoles present 

178 

is greater than on other nearby sites, hi11slopes and 

mesas* 

South Slope * —South-facing slopes above the canyon 

floor support a thin cover of xerophytio desert shrubs 

(Plot 28, Table 23). Bursera mlorophylla. Enoella farlnosa* 

and Fouqulerla splendens locally reach maximum concentra 

tion on the upper slopes near the rim of the canyon, while 

Atrlplex barolayana and Larrea divarlcata increase in dens 

ity toward the bottom of the slope and merge into the 

canyon-bottom communities* Total plant coverage is sparse, 

i*e*, 13$, but equal to that along the canyon bottom (Table 

29)• In contrast to the canyon floor there are fewer num 

bers of speoles present: 2k in the quadrat and 25 in the 

stand. 

North Slopes*—Hills and canyon slopes with north 

exposures do not show much physiognomic difference from 

south slopes and are similarly vegetated with xerophytio 

desert shrubs (Plot 29* Table 29 )• Plot 29 was located 

on the opposite side of the same small interhill valley 

or oanyon from Plot 28* Differences between these sites

TABLE 28 

179 

PLOT 28. ENSENADA BLANCA, I SLA TIBURON, CA. 1/2 KM, INLAND 

(EAST) FROM SHORE, CA. 15-20 M. ELEV. SOUTH EXPOSURE, 195- 

215°, SLOPE 38#. ROCKY, SOUTH-PACING SLOPE OP BROAD CANYON* 


Species 

Number 

(o.l ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

% 

Cover 

age 

Fouquleria splendens 1 13.8 12.1 0.5 

Atamisquea emarginata 1 4.9 - 0.5 

Jatropha ouneata 44 ^•3 3.3 6 

Phaulothamnus spinesoens - 3.9 - - 

Bursera mlorophylla 4 3.5 3.2 0.5 

Larrea dlvarlcata 6 3.0 2.3 0.5 

Lycium ap. 2 2.7 - 0.5 

Lyoium sp. 1 2.3 - - 

Eneella farlnosa 10 2.0 1.7 mm 

Hlbisous denudatus 57 1.9 1.6 - 

Sphaeralcea sp. 4 1.7 - 1.5 

Atrlplex barolayana 183 1.6 1.1 0.5 

Errazurizia megaoarpa 23 1.2 1.1 1.5 

Hoffmanseggla intrioata 37 1.1 0.6 0.5 

Fagonla pachyacantha 0.8 0.8 0.5 

Total 412 13.0 


Allionla incamata 

Amaranthus watsonil 

Antirrhinum oyathiferum 

Boerhaavia cf. ereota 


D1taxis neomexioana 


Euphorbia polyoarpa

Mentzelia adhaerana 

Phaaeolus filiformis 



Total speoles in stands 25

TABLE 29 

181 

PLOT 29- ENSENADA BLANCA, ISLA TIBURON, CA. 1/2 KM. INLAND 

(EAST) FROM SHORE, CA. 15-20 M, ELEV. NORTH EXPOSURE, 20®, 

SLOPE 38^. ROCKY NORTH-FACING SLOPE OF BROAD CANYON. COVER 

AGE CA. 25*. 29 JANUARY 1965 

Maximum Mean 


Speoles (0*1 ha) (ft) (ft) 

Fouquierla splendens 1 11.2 10.7 

Lycium sp. 2 3.3 - 


Bursera microphylla 2 3.0 - 

Sphaeralooa sp. 7 2.2 - 

Lyoium sp. 12 - - 

Condalia globosa 2 2.0 - 

Condalia lycioides 3 2.0 - 

Encelia farinosa 46 1.7 1.5 

Larrea divarlcata 2 1.7 - 

Errazurizia megaoarpa 24 1.6 1.5 


Atriplex barelayana 185 1-5 1.1 

Ditaxis lanoeolata 1 1.4 - 

Ferrocaotus wislizenii 3 1.4 - 

Fagonla pachyaoantha 108 0.9 0.7 

Hoffmanseggia intrioata 28 0.6 - 

Total 561 


Amaranthus wataonii 

Antirrhinum cyathlferum 




Cenohrus palmer1 

Datura discolor

Dl taxis neomexloana 

Dryaarla haloateoidea 



Mentzella adhaerana 

Perltyle oallfornloa 

Peotia of* pappoaa 

Phaaeolua f11Iforala 



Total apeoiea in quadrats 33 

Total apeoles in standi 33

Is seen as a shift In densities of species present and 

minor florlstlc changes. Bursera mlcrophvlla and Larrea 

dlvarlcata are rare as compared with their occurrence on 

south-facing slopes but their presence on north slopes 

lndloates the aridity of the area. Atrlplex barclayana 

183 

Is the most abundant species here and It Is common through 

out the entire north-facing slope. It Is thus present at 

the Yarlous habitat gradients but reaohes greatest develop 

ment on north slopes, along the oanyon bottom, and on the 

lower south-facing slopes adjacent to the canyon bottom. 

Fagonla pachyacantha is almost as common as on the mesas 

(Table 26) and It appears that the environmental condi 

tions simulate the narrow niche which It occupies on the 

mesa. Thirty-three species were present and nearly half 

of these were ephemerals. 

East Coast (Palo Flerro and Santa Rosa) 

An expansive bajada stretches across the east side 

of the Island between the Infemillo shore and the Sierra 

Kunkaak range. It Is the western counterpart of the main 

land bajada of the opposite shore of the Infemillo. If 

the sea were to fall about a fathom much of the Infemillo 

channel would be exposed, these bajadas would constitute 

opposite sides of the same broad valley, and would prob 

ably look similar to the broad Bacuachl valley plain which

Ilea east of Desemboque San Ignaolo. Certainly the Infer- 

nlllo channel was dry during Pleistocene times. Both 

184 

physiognomloally and phytogeographlcally the opposite sides 

of the Infemlllo appear similar but with the obvious 

absence of an extensive cardonal on the Tlburon side* The 

few florlstlc differences are minor and may also be due to 

variation of slope exposure. 

The following series of quadrat studies were 

obtained In the vlolnlty of Palo Flerro and are supple 

mented with data taken between the vicinity of Santa Rosa 

and the east slopes of Sierra Kunkaak• The remaining por 

tion of the east shore bajada substantially conforms to 

the observations given below. 

Palo Flerro Is the name given to the campsite, 

airfield, and estero In the vlolnlty of Punta Tortuga at 

the eastern-central side of the Island (Fig. 40). Santa 

Rosa Is the name used for the large sandy point which marks 

the south end of the Infernlllo channel. 

Shore Zone.—The small estero at Palo Flerro con 

tains well developed mangroves. Large shrubs or small 

trees of Avlcennla germlnans 2.3 to k m. high clog the 

shallow sea water Inlets with nearly Impenetrable thickets. 

Rhlzophora mangle and Laguncularla racemosa are probably 

present but verified collections are lacking from Tlburon. 

Above the usual high tide line, and Intermingling with the

Figure 1 +0. Aerial view showing bajada at east-central side 

of Isla Tiburon; estero and landing field at 

Palo Fierro (oenter). Mainland (background) 

showing Punta Chueoa (sandy peninsula, right 

background) and part of Sierra Seri range. The 

coast-shrub (Frankenla) zone appears as a light- 

colored band near the shore and is dissected by 

dendritic arroyo systems with dense mixed desert 

shrubs appearing dark-colored.

uppermost Avlootmla. are dense mats of suooulent forbs and 

salt grass* These are* 

Bat is marltlma 

Monanthoohloe llttoralls 

Salloornla paolfloa "" 

Seauylum verruoosum 

Suaeda"a p. (not torreyana) 

On successively higher ground Allenrolfea ocoldentalls. 

186 

Maytenus phyllantholdes. and Suaeda torreyana are generally 

oommon, although any of these may abut or Intermingle with 

Avlcennla. 

From the southern edge of the Palo Fierro estero to 

Santa Rosa, saline marshy areas support extensive thickets 

of Maytenus phyllantholdes. The soil is muddy and per 

manently moist, but seldom if ever, inundated by tidal 

waters* At the estero margins it is not uncommon to find 

Maytenus in pure stand with 100# coverage and heights reach 

ing 3.3 to b m., or rarely to oa. 5 nu 

Lower Ba.lada (Frankenla).—The lower bajada along 

the east shore of the island is characterized by a well 

marked Frankenla zone which imparts a greyish cast to the 

landscape (Fig# *H). At its lower edge there are rela 

tively few speoies, but these are of diverse growth-forms 

and may include the following speoies: 

Atriplex linearis 

Fouqulerla splendetis 

Frankenia palmerl 

Maytenus nhvllanthoide s 

Perltyle emorvl 

Suaeda torreyana

Figure 41. Coast-shrub (Frankenia) zone at Santa Rosa, Isla 

Tlburon. Maytenus Dhyllanthold.es (left) and 

Frankenia palmer1•

tm 

m \n\r il

At Palo Fierro most of the lower bajada ends In a series 

of low mesa-like ridges surfaced with pavement-like trans 

ported felolte. These ridges do not extend Inland more 

than 1.5 to 2.5 kms. and support only a meager ooast shrub 

(Frankenla palmerl) oover (Plot 30, Table 30)• The orest 

or oenter of the mesa-ridge is nearly barren except for 

188 

very widely spaced Frankenla bushes which here produce less 

than 2-3* coverage• Twenty speoles are reoorded from the 

50 x 20 m« ridge-top quadrat* However, due to the narrow 

ness of the ridge-crest the majority of the speoies as 

well as individuals occurred at the edge of the quadrat to 

either side of the ridge-crest* Proceeding into the 

adjacent swales a richer vegetation and many more indi 

viduals are quickly encountered (Plot 31* Table 31, Fig* 1*2). 

4«P 

The swale or depression in which Plot 31 was 

located is characteristic of the areas lnterdlgltating 

with the sparsely vegetated coast-shrub dominated ridges 

(Plot 30). These swales are actually the termini of den 

dritic dralnageways which run perpendicular to the shore 

line (Fig. *K>). Plot 31 was placed approximately 50 m. 

away from Plot 30• Here Frankenla plays only a minor role 

and the major plant oover consists of drought-deciduous 

desert shrubs and caoti. 

Local variation in the monotonous low and grey- 

oolored ooast shrub zone ooours on smaller areas in which

TABLE 30 

PLOT 30. PALO FIEBRO, ISLA TIBUBON, CA. 1,5 KMS INLAND 

(WEST) FROM SHORE, CA. 8 M. ELEV. LOU FLAT-TOP RIDGE, 

DESERT PAVEPffilT OF TRANSPORTED FELCITE* 

COVERAGE CA. 6%, Ik FEBRUARY 1965 

Speoles 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Bursera niorophylla 5 **•3 3.8 

Fouquieria splendens 3 4.2 - 

Cordia parvifolia 1 3.5 - 


Sinaondsia ohinensis 2 3.3 - 

Enoelia farinosa 9 3.1 - 

Maohaerooereus gunmosus 1 2.5 - 


Errazurizia megaoarpa if 2.2 1.6 

Hibisous denudatus 35 1.6 1.0 

Franlcenia palmeri 200 1.4 1.1 

Fagonla oalifornioa 2 0.1+ - 

Total 271 


Antirrhinum oyathifenun 


Cryptantha angustifolia 

Dalea mollis 

Dalea parryi 

Ditaxis neomezloana 




Total species in stands 20 

189

TABLE 31 

PLOT 31. PALO FIEHRO, ISLA TIBURON, CAj. 1.5 KMS. INLAND 

(VEST) FROM SHORE, CA. 6 M. ELEV. LEVEL TERRAIN IN SWALE 

BETWEEN DESERT PAVEMENT RIDGES. SILTY-SAND SOIL. COVER 

AGE CA. 80%, 14 FEBRUARY~1965 ~ 

Maximum Mean 



Bursera miorophylla 8 14.3 12.1 

Fouquieria splendens 1 12.5 11.1 

Maohaerooereus gummosus 17 12.3 11.2 


Atamlsquea emarglnata 17 9.1 8.1 

Cordla parvlfolla **3 8.8 7.2 

Olneya tesota - 7.5 - 

Maytenus phyllanthoides 94 7.2 6.4 


Abutilon califoralcum if 6.6 5.6 

Larrea divarloata 8 6.6 5.6 


Janus la oalifomloa 1 6.1 - 

Encelia farinosa 43 4.9 4.3 

Cardiospermum corlndum 2 4.8 - 

Jatropha cuneata - 4.4 - 

Condalla globoaa 1 4.1 - 


Trills oalifornicus 2 3.7 - 



Ruellia peninsularis 12 3-2 

Frankenia palmeri 160 2.2 1.5 

Hoffmanseggia intrioata - 1.9 - 

Total 510 

190


Amaranthus flmbrlatus 




Dalea mollis 

Dalea parryl 



Probosoldea altheifolla 




Total speoles In standi 3^

Figure **2. Swale in lower "bajada, Palo Fierro, Isla 

Tlburon. Maohaerooereus gummoaus and 

Bursera microphylla (right), Pole is 5 

feet*

192

there Is thin overstory of Fouqulerla splendens In addi 

193 

tion to Frankenla palmerl (Plot 32, Table 32, Pig. ^3)* The 

soil Is sandy and the terrain lies about one meter below 

nearby mesa-rldges. Similar communities of Fouqulerla and 

Frankenla occur on widely scattered areas elsewhere along 

the coast of Tlburon and the adjacent mainland where they 

are not restricted to sandy soil but occur also on rooky 

substrates. Other species present In Plot 32 are mostly 

stragglers from mixed desert shrub communities found far 

ther Inland, Ephemerals exceed perennials In number of 

species present but their densities are very low. The 

ephemerals are generally aggregated Into small colonies 

In depressions or catchments at the base of shrubs where 

extra water may collect and penetrate Into the soil. The 

number of species present totals 13 In the 0.1 ha. quadrat 

and In the stand. These figures are lower than those 

among mixed desert shrub communities but higher than may 

be expected among the littoral scrub or shore halophytes. 

Mixed desert shrub species characteristic of the 

bajada plain are encountered along small arroyos which 

cross the coast shrub zone (Table 33» Fig. kO). These 

plants often follow the arroyo single file on each side 

of the streamway. The height of arroyo communities Indi 

cate the marked contrast with the adjacent Frankenla 

scrub. Such gallery stands are essentially continuous

TABLE 32 

194 

PLOT 32. PALO FIEHRO, ISLA TIBURON, CA. 1 KM. INLAND (WEST) 

PROM SHORE, CA. 5 M. ELEV. LEVEL TERRAIN, SANDY SOIL. COVER 

AGE CA. 25%, 15 FEBRUARY 1965 

Speeies 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 


Bursera mlcrophylla 1 6.0 4.9 

Maohaerooereus gummosus - 5.5 - 


Frankenla palmerl 693 1.6 1.2 

Total 708 



Amaraathus fimbriatus 





Oligomerls llnifolia 

Perityle emoryi 

unidentified Gramineae (annual) 


Total speoles in standi 14

Figure 43, Lower bajada, Palo Fierro, Isla Tlburon; look 

ing northeast. Fouquieria splendena and 

Fratikenla palmer!»

195

TABLE 33 

PALO FIERRO, ISLA TIBURON, CA. 1/2 KM. INLAND (WEST) PROM 

SHORE. COMMON ARROYO MARGIN SPECIES IN COAST SlfiUB ZONE 

(FRANKENIA). 15 FEBRUARY 1965. 

Speoles Maximum height 

(ft) 

Pachycereus prlnglel 17.6 

Fouqulerla splendens 15.9 

Desmanthus frutioosus 13.7 

Lemaireooereus thurberl 13.0 

Bursera mlcrophylla 12.2 

Janus la oallfomloa 12.0 

Maohaerooereus gummosus 12.0 

Jatropha olnerea 10.6 

Atamlsquea emarglnata 10.4 

Lyolum sp. 8.2 

Abutlion oallfornlcum 8.0 

Larrea divarlcata 8.0 

Slmmondsla ohlnensls 7.6 

Jatropha ouneata 6.4 

Maytenus phyllantholdes 6.2 

Cardlospermum corlndum 5.9 

Llppla palmer1 5.8 

Trlxls oallfomloa 4.3 

Berglnla vlrgata 3.6 

Enoella farlnosa 3.6 

Atrlplex linearis 3.2 

Frankenla palmerl 1.9 

Herbs Present s 


Cenohrus palmer! 

Dalea parry1 


196

with the mixed desert shrub oommunities of the middle 

bajada plain* The arroyos are not large and seldom exoeed 

1*5 to 2 m. in depth and are usually slightly wider than 

deep* 

Middle Ba.lada.—At approximately 1*7 to 2.5 kms. 

197 

inland (west) from the ooast the pavement-like rook surface 

and ooast shrub (Frankenia) zone ends. Here the ridges 

merge into the main body of the expansive east-shore bajada 

and the vegetation gradually becomes rioher and more oom- 

plex. The bajada slopes so gradually that it appears as 

a plain and the streamways generally form shallow washes 

of a retioulate pattern. Vegetation across the bajada con 

sists largely of desert shrubs which frequently reach 2 m. 

in height and various small desert trees (Fig. 44). Nearly 

all of the leaf-bearing species are drought-deolduous. 

In the region of eootone between Frankenia and the 

mixed desert shrubs of the middle bajada lycoid shrubs, 

large oaoti, and various xerophytlo desert shrubs are 

prominent. The oaoti generally are oommonest within the 

inland or upper limits of Frankenia while the lycoid shrubs 

reach peak development Just beyond the inland limits of 

Frankenia. Common caotl here are: 

Lemaireooereus thurberl 

Lophooereus sohottll 

Qpuntla fulglda 

Machaerocereus aummoaus 

Paohyoereus pringle1

Figure 41*. Middle bajada, several kilometers west of Santa 

Bosa, Isla Tiburon* Euellla peninsularIs. 

Enoella farlnosa, and Olneya tesota. Note 

dense stand of summer-fall ephemeraIs, October 

25. 1963.

198

199 

LoPhooereua is widely scattered through muoh of the remain 

ing middle bajada but other oaoti are usually absent or 

rare farther inland* The lyooid shrubs include desert 

shrubs which exhibit a growth-form convergent with Lyclum* 

These plants have stiff, usually spinescent twigs and small 

simple leaves* They are quickly drought-deciduous, and 

characteristically form broad and spreading tangled growth* 

The stems are photosynthetic and in dry season condition 

they resemble dwarf palo verdes* Characteristic Lyclum- 

like species in this zone includes 

Castela sp* 

Condall'alycioldes - 

Kramerla grayl 

Lyclum SPP. 

Phaulothamnus spinesoens 

Larrea is first encountered towards the inland edge 

of the lyooid shrub zone* Proceeding west (inland) across 

the bajada plain the vegetation gradually becomes richer, 

and species found only along streamways in the lower bajada 

occur away from streamcourses* At any one point on the 

bajada plants along dralnageways tend to be larger in 

stature than those of the adjacent desert flats* 

A quadrat study site was located on the lower part 

of the middle bajada Just inland from the lycoid shrub 

zone, at about 2*5 lcms* west of the shore (Plot 33» Table 

3^)* The terrain is level and surrounded by shallow stream- 

ways of reticulate pattern. Xerophytlc desert shrubs

TABLE 34 

PLOT 33* PALO FIERRO, ISLA TIBURON, CA. 2.5 KMS. INLAND 

(WEST) FROM SHORE, CA. 30 M. ELEV. LEVEL TERRAIN. ROCK, 

GRAVEL, AND L5£M SOIL. COVERAGE CA. 50#. 


Maximum Moan 






Condalia lyoioides 1 6.9 6.4 

Cordla parvifolia 111 6.5 5.9 

Larrea dlvarloata 67 6.5 5.5 

Slmmondsia ohinensis 3 5.9 - 

Atamisquea emarginata 1 5.1 - 


Enoelia farinosa 6 3.7 2.5 

Ruellia peninsular is 28 3.2 2.9 

Haplopappus sonoriensis 2 2.5 2.5 

Hibisous denudatus 10 2.2 1.9 

Hoffmanseggia intrioata 11 1.6 1.4 

Errazurizia megaoarpa 2 1.7 - 

Total 251 


Boerhaavia sp. 


Dalea mollis 


Euphorbia eriantha 


Mollugo oervlana 

Peotis papposa 



200

oharaoterize the dominant species away from streamways, 

e*£*t Cordla parvlfolla and Larrea dlvarloata. Several 

small desert trees or large shrubs including olneya and 

Bursera occur within the plot but appear to be looated 

along the margin of a streamway which has now shifted. 

A total of 23 species ooours within the confines of the 

0*1 ha* quadrat* 

Two quadrats were placed in the middle bajada 

about 4- kms* inland from the shore at Palo Fierro (Plot 

3**, Table 35» and Plot 35 • Table 36)* Plot 3** chosen 

201 

for its zerophytic nature while Plot 35* located oa* 100 m* 

from the formert represents the densest and riohest desert- 

scrub found in the vioinlty* Plot 3^ was also chosen to 

include a maximum area between streamways; however, the 

reticulate streamways are so finely divided here that it 

is difficult to wholly exclude a streamway from a 0*1 ha* 

(50 x 20 m*) quadrat* In these interstreamway islets 

xerophytic desert shrubs form the dominant oover, e*£*v 

Cordla parvifolia» Encella farlnosa, Larrea dlvarloata* 

and Ruellla peninsularls* Plot 35 was seleoted as contrast 

with Plot 3*t> and to inolude maximum streamway area* Char 

acteristic common large shrubs and small desert trees along 

streamways inolude t 

Bursera mlorophylla Colubrlna glabra 

Ceroldlum mlorophvllum Olneya tesota 

Proaopis torrevana

TABLE 35 

202 

PLOT 3^* PALO FIERRO, ISLA TIBURON, CA. k KMS. INLAND (WEST) 

FROM SHORE, CA. 50 M. ELEV. LEVEL TERRAIN, BAJADA. GRAVELLY 

SOIL. COVERAGE CA, $0%. Ik FEBRUARY 1965 

Maximum Mean 


Speoies (o.l ha) (ft) (ft) 

Olneya tesota 2 17.** 16.9 

Prosopis torreyana - 7 - 

Cercidium miorophyllum - l*f.l - 


Bursera miorophylla - 10.3 - 

Cordia parvifolla 19 8.6 7.3 

Larrea divaricata 97 8.1 6.1 

Simmondsia ohinensis 8 7.7 5.6 

Condalia lyoioides - 7.6 mm 

Atamlsquea emarginata 2 mm 


Cardlospermum oorlndum 1 5.^ - 

Llppia palmeri 1 5.3 - 

Abut i Ion oalifomlca 6 5.1 - 

Ruellla peninsularIs 82 l*.l 3.8 

Trixis oallfomioa - *f.O 3.6 

Enoelia farinosa 62 3.9 3.^ 

Errazurlzia megaoarpa 2 3.4 - 

Total 296 

Herbs Presentt 

Boerhaavia ap. 


Dalea parryl 

Datura neomezlcana 

Dltaxis neomexioana 


Euphorbia pedioulifera



Kailstroemla oalifomloa 

Pectis papposa 




Total speoies in standi 30

TABLE 36 

204 

PLOT 35« PALO FIERRO, ISLA TIBURON, CA. 4 KMS. INLAND (WEST) 

FROM SHORE, CA. 50 M. ELEV. LEVEL TERRAIN WITH SMALL SHALLOW 

WASHES. SAND AND GRAVEL SOIL, COVERAGE CA. (>5%. 


Maximum Mean 



Olneya tesota 3 20*5 17*9 

Ceroidium mlcrophyllum 2 15*2 

Desmanthus fruitioosus 2 13*2 8.1 

Prosopls torreyana 2 12.8 

Stegnosperma halimifollum 2 12.4 

Hyptis emoryl - 11.9 



Atamlsquea emarginata - 9.4 

Cordla parvifolia 18 8.3 7-7 

Larrea divarioata 17 7*4 7*3 

Janusia oalifornioa - - 

Viscainoa geniculata 2 6.6 

Cardiospermum corlndum 1 6.4 

Melochia tomentosa 1 5*5 

Simmondsia ohlnensis 33 5*4 4.6 

Enoelia farinosa 13 5*4 4.5 

Ruellia peninsularis 118 5*4 3*6 

Horsfordia sp. 13 4.7 4.5 

Lippia palmeri 1 4.7 

Trixis oalifornica 2 4.4 

Hibiscus denudatus 3 3*0 2.2 


Ceroidium mlcrophyllum - 1«4


P or o phy Hum graoile 2 1.4 

Lyrooarpa ooulteri 3 1.2 

Fagonia califoralca 2 0.9 

Total 249 


Amaranthus watsonli 

Antirrhinum oyathiforum 

Cryptantha angustifolla 

Dalea parryi 


Ditaxis neomexicana 





Kallstroemia oalifomics 


Physails sp. 


Total species in stand: 40 

205

The total number of speoies present in Plot 3*t was 

30 in the stand and 25 in the 0.1 ha. quadrat while in the 

more riohly vegetated Plot 35 species totaled 40 and 3*f 

206 

respectively. The number of perennial and ephemeral speoies 

at Plot 35 is greater than at any of the other quadrat 

sites in the Palo Pierro region. 

Upper Ba.lada.--The upper bajada is rooky and rough 

as a result of outwash from the east slopes of Sierra Kun- 

kaak. Arroyo channels are usually deeper than on the lower 

or middle bajada. The vegetation of the upper bajada is 

largely dominated by small desert trees and mixed desert 

shrubs (Fig. ^5)• Cacti and many xerophytlo desert shrubs 

Larrea divarioata). common on the lower portions of 

the bajada are absent, others are less oommon but the 

individuals reaoh significantly larger stature here. Some 

of the species present on the upper bajada but not occurring 

at lower elevation show affinities with subtropioal scrub 

regions to the south and oocur onto Sierra Kunkaak (©•£• > 

Gualacum coulterl and Thrvallls angustlfolla). 

Sierra Kunkaak.—Higher elevations of Sierra Kun 

kaak contain extensive areas of thomscrub, particularly 

on east-and north-faoing slopes. Close aerial inspection 

of the summit revealed extensive low forests in which 

Lyslloma divarioata and Aoaola wlllardlana are among the 

major dominants. Thornsorub on the east side of the

Figure 4*5. Upper bajada, east foothills of Sierra Kunkaak 

at several kilometers west of Santa Rosa, Isla 

Tlburon; looking east. Sierra Seri (mainland) 

in background. Bursera mlorophylla. Huellla 

peninsular1s» and mixed desert shrubs*

207

mountain follows the narrow interior intermont valleys or 

canyons nearly to the base of the mountain. Canyon floors 

and north- or east-facing slopes in the interior foothills 

or base of the mountain west of Santa Rosa support rich 

208 

groifth of small thomsorub and desertsorub trees and shrubs 

(Fig* 46). Characteristic speoies include: 

Abutlion callfornicum 

Abut lion lncanum 

Acacia w'lllardlana 

Acalypha oomonduana 

Ayenla compaota 

Avenla glabra 

Berglnla vlrgata 

Haplophyton oimlcidum 

Jacoblnla ovata 

Jaoaulnla pungens 

Janusla callfornloa 

Janusla graollls 

Llppla palmerl 

Lysiloma dlvarloata 

Brlokellla ooulteri 

Bumella "oocldentalls 


Calllandra rose57" 

Cardlospermum oorlndum 

Celtis pallida 

Colubrlna glabra 

Coursetfa glandulosa 

Croton _ magdalenae 

Pitaxi8 lance Plata 

Elvtrarla lmbrloata 

Flcus palmerl 

Gualacum ooulteri 

Marsdenla ed tills 

Mimosa Jaxlflora 

Mascagnia macroptera 

MelochlaTtomentosa 

Phaulothamnus splnesoens 

Bandla thurberl 

Ruellla peninsular!s 

Saplum blloculare 

Stegnosperma halTinlfollum 

nalimlfol3 

Thryallis tills angi angustlfolia 

Tragla ia ambl.yo< amblyodonta 

Verpeslna >slna sp. sp. 

South-faolng slopes in the foothills show great 

variation depending largely upon buildup of soil. In 

general Acacia wlllardlana and Lemalreocereus thurberl 

occur together with various desert shrubs (Fig* ^7)* At 

the base of south slopes Euellla penlnsularls may be 

especially abundant. On canyon or valley bottom benches 

it often forms nearly pure stands with 100# oover exoept 

for deer trails which crisscross the valleys and canyons. 

Apparently these benches represent former canyon floor

Figure 46. East foothills of Sierra Kunkaak, west of Santa 

Rosa, Isla Tiburon. Riparian thornsorub. Aoaola 

wlllardlana and Coursetla glandulosa (left); 

Phragmites oommunls (center). Senor Jesus 

Morales is oarrying bundles of carrizo (Phrag 

mites oommunls) to make a model Seri balsa (boat) 

whioh is now at the Arizona Museum* October 26, 

1963.

i •* f- • 

209

Figure b?. East foothills of Sierra Kunkaak, west of 

Santa Rosa, Isla Tlburon. South-facing 

slope.

210

levels or arroyo beds. Desertsorub on south-facing slopes 

extend to near peak elevation and the west faoe of Sierra 

Kunkaak likewise supports desertscrub rather than thorn- 

scrub. 

Tlnajas or canyon waterholes are widely soattered 

through the Sierra Kunkaak range and provide vital oases 

for deer and other animals* The tinajas were oritlcal to 

the survival of the Serls and potsherds often litter the 

211 

trails. Waterpools and seepage are marked by locally dense 

colonies of Fhragmltes communis (Fig. 48). The stems or 

reeds of Phragmltes were employed by the Serl Indians to 

build ocean-going balsas or reed boats (McGee, 1898). 

Figure **8 shows Senor Jesus Morales, a Serl who now lives 

at Desemboque, selecting reeds to be used In building a 

model balsa. 1 

South-Central Region (Sauzal) 

Arroyo Sauzal drains one of the major intermont 

valleys at the south-central end of the island (Fig. ^9)» 

Its broad channel winds through rugged mountains and hills 

in a general north-south direction and produces a complex 

topography. The name Sauzal refers to the well known 

1. This balsa model is now in the oolleotion of 

the Arizona Museum.

Figure ^8. East foothills of Sierra Kunkaak, west of Santa 

Rosa, Isla Tiburon. Phragmltea communis at a 

tlnaja (waterhole)« Seiior Jesus Morales Is pre 

paring bundles of oarrizo (Phragmltea) to carry 

baok to Desemboque.

212

Figure lf9« Aerial view of south-oentral side of Isla 

Tiburon showing Arroyo Sauzal* Note the 

conspicuous marine terrace several hundred 

feet above the present level of Sauzal•

aguaje or waterlog place located at approximately 5 tans. 

Inland from the shore (see pp. 223-230). 

214 

Desertsorub at the south-oentral side of the Island 

appears somewhat more xerophytlo than at the east side of 

the Island (Palo Flerro) but Is decidedly richer than 

the western shore (Ensenada Blanoa). Hillsides, bajadas, 

and pediments generally support sparse mixed desert shrub 

communities and floodplalns and arroyos are characterized 

by mixed large desert shrubs and small desert trees* 

Low Relief Hills and Plains.—Low lntermont areas 

away from streamways show 15 to 18$ coverage with xero 

phytlo desert shrub communities (Plot J6, Table 37; Plot 

37, Table 38). The substrate lnoludes loose rock and 

rough yellowish gravel In a relatively shallow soil pro 

file which Is often extensively tunneled by desert rodents. 

On the surface rodent trails form conspicuous patterns and 

the sparseness of plant cover, particularly the absence of 

cactii may be due In part to the activities of the large 

rodent populations. 

Larger shrubs are widely scattered and gener 

ally aggregated. Smaller shrubs and bushes, e.£«, Encella 

farlnosa, far outnumber the larger ones In total coverage 

and number of Individuals. Encella Is common throughout 

and the populations often consist of nearly the same size 

class, presumably as the result of a high percentage of

TABLE 37 

PLOT 36. SAUZAL, ISLA TIBURON, CA. 1/4 KM, EAST OP ARROYO 

SAUZAL AT CA. 3 KMS. INLAND (NOBTH) PROM SHORE, CA. 25 M. 

ELEV. TOP OP LOW ROLLING HILL. ROCK, GRAVEL, AND LOAM 

SOIL. COVERAGE CA. 15*. 31 JANUARY I965 

Number 

Species (0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Bursera miorophylla 12 9.2 7.^ 

Larrea divarlcata 15 6.5 *.3 


Enoelia farlnoaa 253 2.8 1.7 

Lyoium sp. - 2.7 - 

Cardiospermum corltidum 2 2.7 - 

Hibiscus denudatus 5^ 2.3 1.6 

Perrooactus sp. - 1.9 - 

Hoffmanseggia intrloata 30 1.7 1.3 

Fagonia califomioa Jt1 0.7 0.4 

Total 415 




Ariatida adsoensionia 


Cusouta sp. 

Dalea parryi 



Kallstroemia sp. 


Feotia of. palmeri 

Phaseolus filiformis 




215

TABLE 38 

PLOT 37• SAUZAL, ISLA. TIBURON, CA. 1/2 KM. EAST OF ARROYO 

SAUZAL AT CA. 3 KMS. INLAND (NORTH) FROM SHORE, CA. 30 M. 

ELEV. TOP~^F LOW ROLLING HILL. LIGHT-COLORED SMLL LOOSE 

ROCK AND FINE-TEXTURED SOIL. 31 JANUARY 1965 


Number height height Cover 

Species I [0.1 ha) (ft) (ft) age 

Fouquieria splendens - 12.6 - - 

Olneya tesota 5 11.7 10.7 2.0 

Bursera mlcrophylla u, 9.7 7.2 3.5 

Colubrlna glabra 16 6.9 4.7 2.0 

Lophocereus sohottil - 5.2 - - 

Jaoquemontia abutiloides 43 4.6 1.8 - 

Opuntia blgelovii - 4.3 - - 

Enoella farlnosa 2k9 3.0 2.3 10.5 

Lyoium sp. 1 2.6 - 0.5 

Ruellia peninsularIs 18 2.4 2.2 «» 

Hiblsous denudatus 2 1.7 - - 

Ayenla oompaota 1 0.9 - - 

Total 339 

Herbs Presentx 

Amaranthus watsouli 

Aristlda adscensionls 




Cusouta sp. 

Dalea parry! 





Peotls palmeri 

Fhaseolus flllformls 

Setaria llebmannll 

216


Tephrosla sp. 




Total speoies in stand: 30

survival during a particularly fortuitous season* Summer- 

fall ephemeral sometimes reaohes 100# coverage with Tlde- 

stromla lanuginosa playing a major role. At both quadrat 

sites the number of ephemeral speoies exoeeds perennial 

species* 

Hlllsloues* —The rooky hills scattered through the 

Sauzal region are generally vegetated with desert shrubs 

which seldom produoe more than 10 to 1$% cover* Two hill 

side quadrats were obtained, one on a north-facing slope 

(Plot 38, Table 39) and the other on the south face of the 

same hill (Plot 39• Table 40)* At Plot 38 plant cover was 

218 

oa, 30# with 3k species present while at Plot 39 the cover 

age was only oa* 10# with 30 species* The steeper (43#) &ud 

more eroded south slope may be a result of less vegetation 

cover than on the north slope (24# slope); however, a 

steeper slope gradient may secondarily limit plant growth* 

Flood Plain* —Ma .lor perennials along streamways and 

floodplains inolude rich stands of desert shrubs and trees* 

Larger trees are widely scattered, usually ooourrlng in 

small oolonles, while smaller trees are more oommon and 

often form major elements of the community* Approximate 

ranges of maximum tree heights are indicated below: 

Bumelia oooldentalis 

Flous 

Proaopla torreyai 

Acacia wlllardla 

JaoQUlnla wumcens 

Olneya tesota 

10-12 m* 

8-12 m* 

8-10 m* 

5—10 m * 

7-8 m* 

7—8 m* 

6-8 m*

TABLE 39 

PLOT 38. SAUZAL, ISLA TIBURON, CA. 1/2 KM. EAST OF ABBOYO 

SAUZAL AT CA. 3 KMS. INLAND (NOlOT) FROM SHORE, CA. 40 M. 

ELEV. SMALL ROCKY HILL, NORTH EXPOSURE, 15°, SLOPE 2k%. 

COVERAGE CA. 30J*. 31 JANUARY 1965 

Speoies 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Fouqulerla splendens 3 14.0 12.4 




Janusla gracilis 2 3.3 - 

Lippla palmer1 35 3.2 2.9 

Colubrlna glabra - 3.2 - 

Ruellla peninsularis 23 3.1 2.8 


Krameria gray! - 2.6 - 

Errazurlzia megacarpa 11 2.6 - 

Enoelia farinosa 1 2.4 - 

Hoffmanseggla intricata 38 2.4 1.9 

Tephrosla sp. 189 2.4 2.3 

Jaoquemontia abutiloldes 13 2.1 - 

Ditails lanoeolata 20 2.1 - 

Hiblsous denudatus 235 1.9 1.8 

Thryallls angustifolia 18 1.3 1.0 

Ferrooactus sp. 1 1.1 - 

Carlowrightia sp. 6 1.1 - 

Krameria parvifolia 2 1.0 - 

Ayenla oompaota 8 0.8 - 

Total 634 

219

TABLE 39— Continued 





Bouteloua "barbata 

Dalea mollis 

Dalea parryl 


Kallstroemla sp. 

Peotls palmerl 


Phaseolus flllformls 

Taphroala sp# 

Trlantheaa portulaoastrum 

Total speoles In quadrats 32 

Total species In stands 3^

TABLE 40 

PLOT 39* SAUZAL, I SLA TIBURON, CA. 1/2 KM. EAST OF ARROYO 

SAUZAL AT CA. 3 KMS. INLAND (NORTH) FROM SHORE, CA. 40 M. 

ELEV. SMALL ROCKY HILL, SOUTH EXPOSURE, 205°, SLOPE 43J*. 

COVERAGE CA. 10%. 31 JANUARY 1965 

Maximum Mean 



Acaola wlllardlana 8 13.5 12.9 

Carneglea glgantea - 7»8 - 

Fouqulerla splendens 6 7*8 5.3 

Ceroidlum mlorophyllum 4 6.8 6.4 





Ascleplas subulata 2 3.5 mm 

Errazurlzla megaoarpa 38 3.1 1.8 

Bebbla Junoea 11 2.9 2.6 

Kramerla grayl 2 1.9 - 

Jaoquemontia abutlloides 8 1.7 - 

Dltaxls lanoeolata 25 1.6 1.1 

Hlblsous denudatus 60 1.5 1.2 

Hoffmanseggla Intrloata 35 1.5 1.4 

Cardlospermum oorlndum 11 1.4 - 

Thryallls angustlfolla - 1.0 - 

Carlowrlghtla sp. 3 0.8 - 

Ayenla oompacta 1 0.7 - 

Total 255 

Herbs Present) 



221

Boerhaavia cf. ereota 


Dalea parryi 




Peotls palmeri 

Phaaeolus filiformis 




The composition of valley floor plant communities 

varies greatly with the substratum and elevation above the 

arroyo ohannel or streamway. Thickets of Hyptls emorvl 

are oommon along the gravelly ohannel and reaoh heights 

of 3 to n. Along the valley floor or oanyon bottom away 

223 

from the shifting streambed the vegetation is markedly richer 

and more varied (Plot *+0, Table 41). Perennials oover oa. 

70% of the ground surfaoe and the struoture of the vegeta 

tion is relatively complex. Aoaola willardlana here forms 

a well developed trunk and the Individuals are the largest I 

have seen* It is very oommon although only two large trees 

fell within the quadrat* Forty-five species are recorded 

in the stand and 38 in the quadrat. The habitat supports 

the greatest number of species per unit area in the region. 

Additional species occur over relatively short distances 

from the quadrat site along the same floodplain. Perennials 

exceed ephemerals in number of species by a ratio of slightly 

more than 2; however, the ephemeral flora here is relatively 

extensive with l** speoies present. 

Sauzal Waterhole.—Sauzal (Pigs* 50 and 51) is one 

of the better known watering plaoes on the island and once 

played a vital role in the life of the Serl Indians. 

Besides providing life-sustaining water the Indians utilized 

the extensive stand of carrlzo (Phragmltes communis) to 

build ocean-going balsas (reed boats). There are two main

TABLE 41 

PLOT 40. ARROYO SAUZAL, ISLA TIBURON, CA. 3 KMS. INLAND 

(NORTH) PROM SHORE, CA. 25 M. ELEV. ROCK, GRAVEL, ANS SAND 

SOIL. COVERAGE CA. ?Qf. 31 JANUARY 1965 

Maximum Mean 



Aoaola willardiana 2 21.6 17.4 


Lemaireooereus thurberl 1 14.7 11.8 

Bursera mlorophylla 4 13.3 - 

Stegnosperma halimifolium 3 10.1 - 

Ceroidlum florldum 1 9.6 - 

Hyptia emoryi 38 9.2 7.1 


Vlsoainoa genlculata - 8.5 - 

Desmanthus frutloosus - 7.8 - 

Card10spermum oorlndum 13 7.1 - 

Condalia lyoioldes - 6.9 mm 

Horsfordia alata - 6.8 6.1 

Janusia graollis 3 4.3 - 

Abutilon oalifomloum 1 3.9 - 

Ruellla penlnsularis 247 3.8 3.6 

Llppia palmeri 6 3.8 3.1 

Dltaxls lanoeolata 6 3.8 - 


Errazurlzia megaoarpa 6 3.3 - 


Bebbla junoea 4 2.3 - 

Euphorbia tomentulosa - 1.8 - 

Jacquemontia abutiloldes 57 1.8 1.7 


224

TABLE 4l—Continued 

Tephroala sp. 33 1.7 

Sncella farinosa 9 1.4- 1,2 

Trixls oaliforaloa - 0.9 

Ayenia oompaota 2 0.8 

Fagonia oallfomlca 1 0.8 

Masoagnla maoroptera 2 0.4 

Total 595 



Antirrhinum cyathiferum 


Bouteloua arlstidoides 





Kallstroemia grandiflora 


Feotls palmer! 

Perityle emoryl 





225

Figure 50* Sauzal waterhole, Isla Tiburon. Phramaltes 

communis. Lemaireocereus thurberl. and Paohy- 

oereus prlnglel.

226

Figure 51 • Sauzal, Isla Tiburon, Miss Cathy Moser at one 

of the permanent pools* Ficus palmeri growing 

on rock bank.

ft 'V'W 

ro 

ro

aguajes about 100 m. or more apart and eaoh is marked by 

a separate thicket of Phragmltes. The aguajes are appar 

228 

ently formed by a solid rook substratum and dykes preventing 

rapid peroolatlon of water into the streambed. There are 

perennial pools of water (Fig. $1) and in late spring 

thousands of tadpoles of Bufo punotatus and Soaphlopus 

oouohl occur in the warm shallow water. Fish, however, are 

absent* Well marked deer paths lead to Sauzal and ooyotes 

also frequent the waterhole. The water is highly alkaline 

and rotting Phragmltes produoes a sulphuric odor. 

Riparian vegetation here is essentially evergreen 

but winter oold 1 oauses minor damage to the foliage of 

Phragmltes. Luxuriant new green growth follows the advent 

of warmer weather in spring. Sallx and Tamarlx also show 

brief winter dormancy or semi-dormanoy. Thus the pheno 

logy of the oommunity is keyed more to temperature than 

to the precipitation pattern whloh so severely limits the 

majority of the Gulf Coast vegetation. Most of the per 

manently wet aguaje soils are oovered by Phragmltes com 

munis which forms dense thiokets mostly 3 to 3*5 high. 

The name Sauzal suggests that willow or sauz (Sallx) might 

be prevalent when in fact there is only a small colony of 

1. It is unlikely that temperatures fall below 

freezing.

moderate-sized shrubs of Salix gooddlngll. 3alix may have 

onoe been more extensive when Phragmites was being har 

vested by the Seri Indians or before Tamarlx became estab 

229 

lished, and either (or both) may have subsequently replaced 

most of the Salix. Tamarlx pantandra is native to the old 

world (Mason, 1959l Wiggins, 1964) and may have been brought 

here by migratory birds. It is a persistent weed along 

roadsides and irrigation ditches near cultivated fields 

in the Sonoran Desert, and has become extensively natural 

ized along the lower Colorado River (Mason, 1959) and the 

r£O Sonoyta. 

Alkaline surface encrustations are evident here and 

characteristic alkaline-adapted species are common, e.g., 

Dlstlohlls splcata. Hellotroplum ourassavloum. and Tamarlx 

pentandra. Plants confined to shallow water and damp or 

wet soil are listed below in their approximate order of 

abundance and height: 

Phragmites oommunls 

Tamarlx pentandra 

Typha domlnaensls 

Baccharls glutlnosa 

gallx gooddlngll 

Stemodla durantTfolla 

Hellotroplum ourassavloum 

Dlstlohlls spToata 

culata 

Plumbago scandens 

Consplouous species found near the waterhole but not 

restricted thereto inoludet

Bumella occidentalIs 

Ceroidlum florldum 

Flcua palmer1 


Mascagnfa maoroptera 

Prosopls torreyana 

Interior or Upper Central Valley 

Vegetation studies were made in the southwest end 

or upper reaohes of the island's central valley and on the 

adjacent slopes in the vlolnlty of latitude 28° 57' N. and 

longitude 112° 27* W.# at 20 to 21 kms* south of Teoomate* 

The valley floor here is approximately 200 m* elevation 

and immediately to the west an arm of the Sierra Menor 

230 

range reaohes J*6o m. elevation* At one time a band of Serl 

Indians occupied the interior region of the island for at 

least part of each year (Moser, 1963)* However, middens 

and potsherds which are so abundant around the periphery 

of the Island were not found here. Thus for more than half 

to three quarters of a oentury the area has not been 

Inhabited and before this time there were probably only a 

relatively small number of indigenous people. The total 

absenoe of present-day depredations by man is evidenced 

by the presence of many gargantuan and seemingly old indi 

viduals of several speoies of trees and shrubs whioh here 

become truly arboresoent, £•£•» Bumella occldentalls (Fig* 

52), Condalla globosa* and Koeberllnla splnosa.

Figure 52• Upper end of central valley, Iala Tiburon. 

A large Bumella oooldentalis (12 high)* 

February 18, 1965*

231

Vegetation in the upper central valley region con 

sists wholly of desertscrub even to peak elevations of the 

232 

adjacent Sierra Menor range. Along streamway margins there 

is rich and varied arboresoent and semi-arborescent growth 

while non-dlsseoted flats consist largely of monotonous 

stands of creosotebush scrub (Iarrea dlvarlcata). On the 

adjaoent east side of Sierra Menor there are highly diverse 

communities of mixed desert shrubs, various small desert 

trees, and shrub and tree caoti. Exposure and elevatlonal 

differences produoe marked variation in the vegetational 

gradients. In general east-facing slopes and higher eleva 

tions support a more varied and richer growth than adjacent 

west and south slopes and lower elevations. 

Valley Plain.—Much of the valley plain away from 

streamways at the western edge of the upper oentral valley 

contains a nearly pure stand of Larrea dlvarlcata (Plot 41, 

Table 42, Fig. 53)* Coverage values for Larrea with 5 

coverage-stick readings showed a range of 6 to 12# and an 

average of 9*2%, The remaining 14 species recorded are 

ephemerals. This is the highest ratio of ephemeral to 

perennial species recorded in the Gulf Coast of Sonora and 

is matched only in parts of the arid regions at the head 

of the Gulf. Both summer-fall and winter-spring species 

are well represented. The phytogeographlc affinities of 

the creosotebush sorub species are with arid desert regions

TABLE k2 

PLOT 1*1. UPPER CENTRAL VALLEY, ISLA TIBURON, CA. 200 M. 

ELEV. VALLEY PLAIN, FINE-TEXTURED SOIL WITH MUCH ROUGH 

GRAVEL AND SHALL ROCK. 1 FEBRUARY 1965 

233 


Number height height Coverage 


Larrea dlvarloata 212 ^.9 *K0 9.2 






Cryptantha angustlfolia 

Cryptantha marltlma 

Cusouta sp. 

Dalea mollis 



Nama hlspldum 

Ollgomerla llnlfolia 

Olneya tesota (seedlings) 

Peotls of. papposa 


Total speoies In quadrats 16 

Total speoies In standi 16

Figure 53* Upper end of central valley, Isla Tlburon. 

Larrea dlvarlcata. Pole Is 5 feet.

234

to the north. Seedling or small plants of Olneya tesota 

are abundant In the Larrea flats but seldom reaoh more 

than 30 cms. high* They germinate during the summer rains 

and many survive through the winter and early spring but 

ultimately perish during the following pre-summer drought. 

The seeds oome from mature Olneya tesota along adjacent 

or nearby arroyo margins where it is common. 

Extensive areas of valley plain in the upper val 

ley apparently once were major watercourses or floodplalns 

235 

which have slnoe been isolated by meandering and now deeper 

out arroyo beds. The vegetation here (Plot *f2, Table 1*3) 

is physlognomlcally Intermediate between that of the 

adjaoent arborescent arroyo margin communities and the 

relatively depauperate Larrea flats. The surface is gener 

ally coarse and uneven, and consists largely of transported 

rock and gravel. Large specimens of Ceroldlum mlorophyllum 

dominate the landscape and are widespread in the coarse- 

soiled ex-floodplain. About half of the 37 speoles present 

are ephemerals and the perennial species include a variety 

of growth-forms of which desert shrubs and small trees are 

the dominant elements. Two stem succulents are present: 

Wllcoxla striata which is relatively common and Lopho- 

cereus schottll. widely scattered but not common. 

Streamways.—An extensive dendritic arroyo system 

drains northward through the central valley (Fig. 57» P* 250)

TABLE 43 

PLOT 42. UPPER CENTRAL VALLEY, ISLA TIBURON, CA. 200 M. 

ELEV. VALLEY PLAIN, COARSE GRAVEL AND ROCK SOIL. COVER 

AGE CA. 20#, 2 FEBRUARY 1965 

Maximum Mean 



Ceroldium miorophyllum 3 13.4 10.5 


Randla thurberi 10 6.7 5.7 

Cfcnmlcarpus soandens - 6.3 - 

Mimosa laxiflora 6 6.2 6.0 


Janus la callfomloa 5 5.2 - 

Lophooereus schottil 1 4.9 - 

Prosopis torreyana 1 4.6 - 

Simmondsia chlnensls 14 4.4 4.0 

Trixis californica 15 4.4 2.7 

Berglnla virgata 25 4.3 4.0 

Lyoium sp. l 4.2 - 

Abutilon ineanum 2 3^ - 

Abutllon oalifornioum - 2.8 - 

Brickellia coulter1 2 2.8 

Kramerla parvifolia 10 2.8 2.2 

unidentified Asclepiadaceae 

(vine) 1 2.4 - 


Porophyllum graoile - 1.7 - 

Carlowrightia sp 3 1.7 - 

Phoradendron oalifornioum 1 - - 

Total 205 

236



Arlstlda adsoenslonis 

Boerhaavia of* ereeta 

Bouteloua barbate 

Cusouta sp. 

Dalea mollis 






Kallstroemla grandlflora 

Panioum hirtloaule 

Peotla of. papposa 

Phaseolus fillformis 

Setaria sp, (annual) 

Tephrosla sp. 

Total speoles in quadrats 36 


and finally terminates at Bahfa Agua Dulce at the north 

shore. These streamways support rich gallery growth of 

238 

small trees and large shrubs with an undergrowth of smaller 

shrubs and herbs* Diversity and stature of the arroyo mar 

gin scrub varies directly with size of the arroyo. A repre 

sentative stand along a moderate-sized arroyo was chosen 

for analysis (Plot 43, Table Mf, Pigs. 5^ and 55) • Peren 

nial species here produce ca. Q0% coverage and larger 

arroyos nearby support stands with up to 100$ coverage. 

Forty speoles were found along the arroyo margin quadrat 

site and 32 of these ocourred within the confines of the 

0.1 ha. plot. Additional species are encountered over rela 

tively short dlstanoes along the streamways. Ephemerals are 

well represented and especially abundant in light shade and 

on the north side of trees and larger shrubs. Olneya 

tesota is the most conspicuous element in the community, 

widespread throughout the valley drainage systems, and 

generally exceeding any other single species in coverage. 

Larrea extends into the periphery of the arroyo margin com 

munities from the adjaoent flats where it attains greater 

height than on the flats, but it apparently occurs in 

reduced numbers (density). 

A recent shift in the streamway Is evident at the 

edge and adjacent to Plot 4-3 (Figs. 5^ and 55)• Shifting 

and meandering streamcourses or arroyos, a continuous

TABLE 44 

PLOT 43* UPPER CENTRAL VALLEY, ISLA TIBURON, CA. 200 M. 

ELEV. ARROYO, GRAVELLY SAND SOIL. COVERAGE CX7 80#. 


Species 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Olneya tesota 7 22,5 18.6 

Condalla globosa 4 17.2 - 

Stegnospema halimlfolium 1 17.2 12.7 


Koeberlinia spinosa 13 11.9 - 

Celtis pallida - 10.6 9.6 

Atamisquea emarglnata 5 8.3 7.7 

Commioarpus soandens 11 8.2 7.8 

Lyoium sp. 13 8,2 7.2 

Larrea divarioata 103 7.9 7.0 

Simmondsia ohinensis - 7.2 6.6 

Lophooereus sohottii - 6.3 - 

Tragia amblyodonta 14 6.3 - 

Phaulothannus spinesoens - 6.0 - 

Hymenoclea monogyra mm 5.6 - 

Briokellia ooulteri 9 5.5 5.2 

Berginia vlrgata mm 4.1 2.7 

Trizis oalifornioa 1 3.8 - 

Asolepias subulata - 3.3 3.2 

Abutilon oalifomicum 19 2.9 «• 

Haplopappus sp. - 1.1 - 

Mimosa laziflora 2 - - 

Lyrooarpa ooulteri 78 mm - 

unidentified Asolepiadaoeae 

1 - - 

Total 285 

239


TABLE Mf—Continued 

Aaaranthus watsonii 

Andraohne oiliato-glandulosa 


Di dipt era resupinata 






Kallatroemla grandiflora 

Lotus tomentellus 

Feotis of* papposa 


Tephrosia sp. 




Figure 5^* Upper end of central valley, Isla Tiburon. 

Olneya tesota* Proeopla torreyana. Ephe- 

merals in right foreground are primarily 

Amaranthus watsonil and Boerhaavia sp> Pole 

is 5 feet* Note older arroyo bed to left of 

pole*

241

Figure 55 • Upper end of central valley, Is la Tiburon. 

Olneya tesota along old arroyobed. Larrea 

dlvarloata on left. Pole is 5 feet.

242

phenomenon of the valley plain, is clearly evident here. 

As the streamway shifts the large shrubs and trees char 

acteristic of the arroyo margin eventually die and the 

arroyo bed fills with herbaceous growth and soil* For a 

while the reoently extinct streamway is discernible as a 

21*3 

shallow swale filled with grasses and forbs (Fig* 55) • If 

the new watercourse remains nearby some of the larger shrubs 

and trees may persist for yearss however, there is no suo- 

oessive generation of arroyo margin speoles along the old 

streamway* Eventually, as the old arroyo bed fills in, 

the gallery vegetation perishes, and it is replaoed by 

Larrea scrub* 

Long lines of dead and eroded ironwood stumps are 

often present in the creosotebush flats* That these stumps, 

seemingly very old, were onoe growing along an arroyo mar 

gin of slightly lower elevation is evidenced by the fact 

that the crown of the stump is usually burled 2 to 4 deci 

meters* Every stage in this dynamic erosion-directed cycle 

is present and evident in the upper valley* 

Mountain Slopes*—The southern part of the Sierra 

Honor range at about the latitude of the southern end of 

the central valley rises to approximately 670 m* elevation* 

Studies were made on an eastward arm of the range which lies 

about 1 km* west of the other quadrats at the upper oentral 

valley* In general the desertsorub here appears richer than

at the northern end of the range, e*£., vest of Teoomate. 

244 

However* the elevations are higher at the southern station. 

Two 0*1 ha* quadrats were obtained on the east 

slope of the mountain, one at oa* 300 m* elevation (Plot 44, 

Table 45)» and the other on the same slope but at oa* 450 m* 

elevation (Plot 45» Table 46). The east slopes to nearly 

330 m. elevation support mixed desert shrubs* Above 330 m* 

a few arborescent or semi-arboresoent species beoome preva 

lent (Figs* 56 and 57)» *•&•» Aoaola wlllardlana. Ceroldlum 

mlorophyllum* Caraeglea gjgantea* and Lemalreooereus thur- 

berl* In Plot 44 a total of 30 speoles were present within 

the quadrat and 31 in the standa while at the higher eleva 

tion of Plot 45 the number of species was 34 in the quadrat 

and 38 in the stand* Fourteen species of ephemerals were 

present in both quadrats* 

Desertscrub on the south-facing slope of the same 

ridge (,i*e*, sites of Plots 44 and 45) is relatively sparse 

and at about 330 m* elevation perennial coverage totals oa* 

20%. Plant heights and number of species present appear to 

be less than on other slope exposures* Prominent south 

slope perennials include: 

ceroldlum micropnyxiui 

Desmanthus frutlcosus 

Encella7arlnosa 

Fouaulera splencTens 

Horsfordla alata 


Larrea (flvarloata 

Lemalreooereus tKurberl 

Olneya tesota

TABLE 45 

245 

PLOT 44. ABM OP SIERRA MENOR AT UPPER CENTRAL VALLEY, ISLA 

TIBURON, CA. 300 M. ELEV. EAST EXPOSURE, 95°, SLOPE 23#. 

ROCK SLOPE? WITH SHALLOW POCKETS OP SOIL. COVERAGE CA. 50%. 


Species 

Number 

(0.1 ha.) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 



Larraa dlvarloata 1 5.1 mm 

Condalia lyoioides 1 5.0 - 

Llppia palmer! 12? 4.8 4.0 



Ditaxls lanoeolata 51 4.6 - 


Phaulothamnus spinesoens - 4.6 mm 


Berginia virgata 133 3.5 2.8 

Enoelia farinosa 144 3.5 3.0 

Trixis oalifomioa 1 2.8 mm 

Krameria gray! 5 2.4 - 


Fagonia oalifomioa 121 1.2 0.9 

Ayenia oompaota 3 0.8 - 

Total 685 



Ar1stIda adsoensionis 

Bouteloua arlstidoldeB 



Dalea parry!

TABLE ^5—Continued 



Kallstroemia grandlflora 

Peotis palmeri 



Setaria llobmannil 




TABLE 46 

24? 

PLOT 45. ARM OP SIERRA MENOR AT UPPER CENTRAL VALLEY, ISLA 

TIBURON, CA. 450 M. ELEV. EAST EXPOSURE, 70°, SLOPE 21J*. 

ROCK SLOPES WITH SHALLOW POCKETS OF SOIL. COVERAGE CA. 50£. 


Maximum Mean 


Species (0*1 ha) (ft) (ft) 

Aoaela wlllardlana 12 17.8 15.5 

Cameglea glgantea - 15.0 aw 

Fouqulerla splendens 10 14.8 14.0 


Lemalreooereus thurberl - 11.2 - 

Ceroldlum mlcrophyllum 5 8.9 - 

Bursera mlorophylla 18 8.1 7-5 



Lyolum sp. 4 4.2 •a 

Saplum bllooulare 1 4.1 - 

Croton sonorae 44 3.6 2.9 

Larrea dlvarloata mm 3.4 - 

D1taxis lanceolata 82 3.2 2.8 

Llppla palmer1 161 3.2 3.1 

Wllooxla striata 1 3.1 - 

Berglnla vlrgata 276 2.8 2.5 


Colubrlna glabra 2 2.2 - 

Kramerla grayl 31 2.2 - 

Ferrooactus wlsllzenll 1 2.1 

Trills oallfornlca 14 1.8 - 

Enoella farlnosa mm 1.4 - 

Mammlllarla sp. 1 - - 

Total 838



Alllonla lnoarnata 



Aristlda sp« (perennial) 

Boerhaavla cf. ereota 

Bouteloua arlstldoides 


Dalea parryl 



Fectls of. pappoaa 


Setaria liebmannll 

Tldestromia lanuginosa 

Total species in quadrats 

Total species in stand: 

3k 

38 

2^8

Figure $6• Upper oentral valley, Isla Tlburon. Looking 

northeast from arm of Sierra Nenor* Jatronha 

cuneata. Aoaola wl 1 lard 1 ana. Carnegiea glgan- 

tea. and Ceroldlum mlorophyllum in foreground 

on southeast-faoing slope. Llght-oolored area 

in middle oonslsts primarily of Larrea dlvari- 

oata sorub. North end of Sierra Kunkaak range 

In background,

249

Figure 57• Looking east from arm of Sierra Menor range 

adjaoent to upper central valley, Isla Tiburon. 

Sierra Kunkaak in background. Acacia wlllard- 

lana and Olneya tesota. Pole is 5 feet (left).

250

North-facing slopes of the same ridge show the 

251 

densest perennial growth in the area with ca« 75% coverage 

above 330 m. elevation. Common speoies found here inoludes 


Ceroldlum mlorophvllum ^ 

Croton sonorae 

Enoelia farinosa 

Fouaule'rla splendens 

Horafordia alata 

Larrea dlyarlcata 

Llppia palmer! 


Trixls oalifomlca 

The west side of the same mountain ridge drops off 

abruptly into rook slides with a relatively sparse cover of 

xerophytic desert shrubs and a few small desert trees (Fig. 

58). Near the ridge ooverage is ca. 25/6# most of which is 

produced by the following species. 


Ceroidlua mlorophyllum 

Fouqule'ria gplendens 


Larrea cTlvarlcata 

Larrea thus ranges to peak elevations on these arid slopes 

but develops greater density on south and west-facing 

slopes than on east and north slopes. Olneya tesota. 

generally characteristic of the valley plain arroyos, is 

here a facultatively dwarfed shrub. 

North Coast (Tecomate) 

Teoomate is located at the northwest end of the 

island on the shore of BahXa Agua Duloe. It was once a

Figure 58. Arm of Sierra Menor, west of upper central 

valley, Isla Tiburon. Looking north, show 

ing west-facing slope in foreground* Bursera 

mlorophylla. Ceroldlum mlorophyllum. Jatropha 

curie a ta, and Larrea dlvarloata.

Mfi\FAWW \ 

MjlsSh•'

principal Seri village and was occupied as recently as 

1952 but today it is seldom used except for fishermen who 

occasionally camp along the shore. 

Shore Zone.—'Localized halophytic littoral growth 

occurs in marshy alkaline soils at the west end of Bahfa 

Agua Duloe. The soil is usually saline or alkaline moist 

hut without tidal sea water which may in part explain the 

absence of mangroves. Large and dense mats or mounds of 

succulent and evergreen species are comprised of Atriplex 

barclayana. Batls marltlma, Maytenus phyllanthoides. and 

Suaeda torreyana. 

A Frankenla palmer1 or ooast shrub zone is dis 

cernible along a narrow coastal strip on rocky hills, 

coastal dunes, and level terrain. It is not as clearly 

delimited nor as extensive as on the east shore of the 

island (Palo Pierro) and the opposite Sonoran mainland. 

High beach dunes front the shore of Bahfa Agua 

Dulce and form distinctive landmarks. Plant oover is thin 

and highly variable, richest on the leeward, sides and on 

the relatively more stable dunes. Common dune species 

include: 

Abronla marltlma 


Croton callTornlcus 

Dalea emoryi 

Euphorbia petrlna 



253

At the east end of the hay dunes extend inland for several 

kilometers and sand has piled against the windward side of 

the rooky hills bordering the east side of the oentral 

valley. These dunes, with their long axis parallel to the 

north shore, are direotly in the path of prevailing winds 

and may not represent anoient beaches. 

Valley Plain.—Non-diBseoted desert plains stretch 

254 

aoross much of the oentral valley and extend from the vicin 

ity of Teoomate to the south end of the oentral valley 

(upper oentral valley station). For the most part these 

plains support oreosotebush scrub in which the most preva 

lent and widespread major perennials inolude Larrea dlvarl- 

oata, Enoella farlnosa. and Errazurlzla megaoarpa« Larrea 

is invariably oommon but Enoella and Errazurlzla are inde 

pendently present or absent. Shrub cover in these communi 

ties usually attains a maximum height of 1.5 m. or less and 

only rarely exoeeds 2 m. Perennials cover 10 to J0% of the 

surface while ephemerals may temporarily produce much 

greater ground cover. 

Two quadrat studies sites were obtained among Larrea 

scrub at Tecomate (Plot 46, Table 47; Plot 47• Table 48). 

Plot 46 was ohosen for sparseness of plant cover and Plot 47 

for its relatively greater density and diversity. Plot 47 

was looated closer to the floodplaln and at oa. 2 m. lower 

elevation than Plot 46. At Plot 47 a total of 24 speoies

TABLE 47 

255 

PLOT 46. TECOMATE, ISLA TIBURON, CA. 1,5 KMS. INLAND (SOUTH) 

PROM SHORE, CA. 15 M. ELEV. VALLEY PLAIN; ROCK, GRAVEL, AND 

LOAM SOIL. COVERAGE CA. 10#. 12 FEBRUARY 1965 

Maximum Mean 


Species (0.1 ha.) (ft) (ft) 


Atamisquea emarglnata - 7.7 - 

Larrea dlvarioata 40 4.8 4.0 

Errazurlzia megacarpa 9 4.0 2.7 

Enoelia farinosa JiL 3.4 20 

Total 101 


Aristlda adsoensionis 




Dalea mollis 

Dltazls neomexloana 




Peotls papposa 

Tidestromla lanuginosa 



Total speoles in stand: 1?

TABLE 48 

PLOT **7* TECOMATE, ISLA TIBUHON, CA. 1 KM. INLAND (SOUTH) 

FROM SHORE, CA. 12 M. ELEV. VALLEY"7LAINt ROCKY LOAM SOIL. 

COVERAGE CA. 25#. 13 FEBRUARY 1965 

Maximum Mean 


Speoles (0,1 ha) (ft) (ft) 


Fouqulerla spiendens - 11.6 

Jatropha oinerea 7 9,2 8*3 

Atamlsquea emarglnata 1 7.7 7*1 

Cercidium florldum 1 6*5 

Larrea dlvarloata 40 6.3 5*1 

Simmondsla ohinensls - 5*1 

Trizls callfornloa - k.6 

Olneya tesota 2 - 

Koeberlinla splnosa - 3*6 

Encella farlnosa 91 3*3 3*1 

Errazurizla megaoarpa 98 2.3 2.0 

Hoffmanseggia intrioata 10 2.0 1*7 

Total 124 






Cuscuta sp* 

Dalea mollis 

Ditaxis neomexicana 



Nlootlana olevelandii 



Total speoies in stands 

256

were present in the stand and 20 in the quadrat while at 

Plot 46 only 17 and 16 speoies respectively were present. 

At Plot 46 the number of perennial (5) is surprisingly low 

and the ratio of ephemeral to perennial species is 2.4. 

Comparing the two stands it is seen that the number of 

ephemerals is about the same, I.e., 12 species in Plot 46 

and 11 in Plot 47* Thus the variation between the two 

stands is primarily a dlfferenoe in perennials, both as to 

number of speoies present and population size. Vines and 

succulents including oaotl are absent from both sites. 

There is extensive rodent tunneling throughout the Larrea 

257 

scrub regions of the valley plain and absence of succulents 

may be due to the rodent populations. Small arroyos or 

gullies in the Larrea plains support narrow and frequently 

interrupted files of larger desert shrubs or rarely small 

desert trees, e.g., Bursera alorophvlla. Koeberllnia spln- 

osa. and Prosopls torreyana. but here they seldom reaoh as 

large a size as in the nearby floodplain or larger arroyos. 

Floodplain.—As the dendritic arroyo system of the 

central valley drains northward it oonverges into a flood- 

plain which terminates in the vicinity of Teoomate and 

drains into Bahfa Agua Duloe. The meandering channels have 

left several successive higher levels of old floodplain 

surface which today appear as islets or benches near the 

present channels. Small desert trees, mixed desert shrubs,

and various undergrowth plants and several vines are com 

mon. Caoti and suooulents are rarely present. 

Two 0.1 ha* quadrats were plaoed along the Arroyo 

258 

Agua Duloe, one on a low benoh (Plot 48, Table 49)» and the 

other in the present floodplain (Plot 49, Table 50)* Snail 

trees and large shrubs, e.g., Bursera mlcrophvlla. Olneya 

tesota, and Prosools torrevana. dominate the landscape* 

The number of mature individuals of these speoies within 

a 0.1 ha. quadrat (50 * 20 m.) are few, due to the rela 

tively broad orown spread of an individual plant, and for 

these speoiiss the 0.1 ha. quadrat does not provide an 

adequate means of oomparison. Olneya seems to be the most 

widespread and regularly spaced major perennial in the 

flood plain. 

The site of Plot 48 is on a benoh which appears to 

have been part of an older flood plain channel. Coverage 

is ca. 20$ and 38 speoies were encountered in the stand, 

of whioh nearly half are ephemerals. Phoradendron oall- 

foralcum, a parasite on Olneya and Prosopla. is the only 

aphyllous species present. 

Plot 49 was plaoed in a representative stand in 

the present floodplain. Bursera mlorophylla. Olneya tesota. 

prosopls torreyana and many shrubs are common, and maximum 

heights (Table 53) generally exceed other vegetation in 

the Tecomate region. Speoies composition along the

TABLE 49 

259 

PLOT 48. TECOMATE, ISLA TIBURON, CA. 2 KMS. INLAND (SOUTH) 

FROM SHORE, CA. 10 M. ELEV. LOW BENCH ADJACENT TO FLOOD- 

PLAIN OF ARROYO AGUA DULCE. ROCK, GRAVEL, AND SANDY-LOAM 

SOIL, COVERAGE CA. 20J6. 13 FEBRUARY 1965 

Maximum Mean 


Species (0.1 ha). (ft) (ft) 

Prosopis torreyana - 17.2 - 


Simmondsia ohinensis 52 9*3 6.1 

Aoaoia greggii 4 7.2 6.6 


Cardiospermum oorindum 3 6.3 - 

Atamisquea emarginata - 6.3 - 

Larrea divarioata 2 5.6 - 

Lyoium sp. - 5.6 5.5 

Viscainoa geniculata 6 5.5 5.2 

Condalia globosa 3 5.3 5.2 

Condalia lyoioides - 4.2 - 

Enoelia farlnosa 3 3.2 3.2 

Ditaxis lanceolata 1 2.3 - 


ftuellia peninsularis 16 2.2 2.0 


Porophyllum graoile 4 1.4 1.2 

Dalea parryi 3 0.9 - 

Phoradendron oalifornioum 1 - - 

Total 133 



Aristida adseensionis 

Boerhaavia sp.




Cuscuta sp. 

Dalea mollis 

Dalea parryi 




Hentzelia adhaerans 

Mollugo oerviana 

Nlootlana olevelandli 

01IsomerIs llnlfolla 




Total speoies in quadrats 3^ 

Total speoies in standi 38 

260

TABLE 50 

261 

PLOT 4-9. TECOMATE, I SLA TIBURON, PLOODPLAIN OP ARROYO AGUA 

DULCE, CA. 1 KM. INLAND (SOUTH) FROM SHORE, CA. 8 M. ELEV. 

ROCKY GRAVEL AND SAND SOIL. COVERAGE CA."To£. 

12 FEBRUARY 19^5 

Maximum Mean 



Olneya teaota 3 25*8 20.4- 

Prosopls torreyana - 16.8 

Bursera miorophylla - 12.1 

Simmondsia ohlnensls 68 9«5 6.3 

Ceroidlum floridum - 8.8 - 

Jatropha cinerea 1 7*5 

Aoaoia greggli 60 7.*f 6.6 

Lycium sp. 20 6.8 

Atamisquea emarginata 1 7*2 

Colubrina glabra 7 7*1 

Stegnospermum hallmlfollum - 6.7 

Vlsoalnoa genioulata 12 6*5 5*9 

Ditaxis lanoeolata 1 6.2 

Cardiospermum oorlndum 3 5*2 

Condalia lyoloides - 5*2 

Horsfordia alata 1 • 

Enoelia farinosa 2 ^.2 3,1 

Abutilon oallfornicum 1 ^.1 

Condalia globosa 1 3*9 


Errazurizia megaoarpa 2 2*3 2.1 

Porophyllum graoile - 1.2 

Lyrooarpa ooulteri 3 1.2 

Total 196








Euphorbia polyearpa 



Mentzelia sp* 

Niootlana olevelandll 

Oenothera of* leptocarpa 


Total speoles in stand: 3^

floodplaln shows much variation over relatively short dis 

tances* Floodwaters seasonally nay produce marked changes 

or shifts of the gravelly and rooky surface* Large local 

ized colonies of seedlings often spring forth following a 

storm but the mature plants do not seem to be unusually 

aggregated. Locally dense stands of Hyptls emoryl and 

Hymenoolea monogyra often ooour along the Immediate arroyo 

margin and often extend Into the sandy arroyo bed. Ephe- 

263 

merals are plentiful but do not seem to be as well developed 

as on other habitats at Teoomate. 

Hill slopes .—The northern extremity of the Sierra 

Menor range lies approximately 1 km. west of the village 

site of Tecomate. Its slopes support mixed desert shrubs, 

a few small desert trees, and oolumnar caotl. The vege 

tation generally becomes richer on east- and north-facing 

slopes and toward higher elevation. Agave subBlmplex and 

Ascleplas albicans become common above 200 m. elevation. 

Notholaena oallfornlca. the only fern collected on Tiburon, 

was found on north slopes among the voloanlo rooks. Hock- 

adapted xerophytlo species are common on south-facing slopes 

and includes 

Carnealea glgantea 

Cerclalum mlcrophyllum 


Lemalreocereus thurberl 

Pachyoereus prIngle1

264 

Both Paohyoereus and Carneglea ooour together; however, the 

former show greatest development on lower slopes with east 

exposure while the latter reaches maximum density and size 

on the more arid south-faoing, higher, and steeper slopes. 

A quadrat study was obtained on the lower east 

slopes (Plot 509 Table 51) at several hundred meters west 

of Plot 46 (Table 4?). Fouaulerla splendens* Jatropha 

ouneata. and Larrea divarloata form the most oonspiouous 

elements in the landsoape and several oaoti are also 

present* The xerophytio nature of the oommunity is further 

shown by the relatively high percentage of ephemerals which 

slightly outnumber the perennials* 

Summary.—The wholly natural vegetation of Isla 

Tlburon includes an extensive area of thornsorub on Sierra 

Kunkaak > several mangrove esteros along the Infemillo 

coast* and desertsorub of diverse nature covering most of 

the island. Desertsorub oonsists largely of mixed small 

desert trees and shrubs* Extensive areas of simple com 

munities dominated by Larrea divarloata ooour on the plains 

of the oentral valley* 

Desertsorub of the west side of the island is con 

spicuously xerophytio* A significant portion of the flora 

here does not occur on the Sonoran mainland at the same 

latitude nor on the relatively more meslo eastern part of 

the island* These speoies characteristically ooour also

TABLE 51 

265 

PLOT 50* TECOMATE, ISLA TXBURON. LOW HILL AT EAST BASE OF 

SIERRA MENOR, CA. 1/2 KM* WEST OF VILLAGE SITE, CA. 30 M. 

ELEV. NORTHEAST EXPOSURE, 65°, SLOPE 22^. COVERAGE CA* 20%. 

ROCKY SOIL. 12 FEBRUARY 1965 

Maximum Mean 


Speolea (0.1 ha) (ft) (ft) 

Fouquleria splendens 10 13.8 12.9 


Lemairaooereus thurberl - 8.2 - 

Ceroid lum mlorophyllum 1 6.5 - 



Lyolum sp. 1 5.1 - 

Errazurlzla megaoarpa 6 3.0 - 

Enoella farlnosa 4 2.4 2.3 

Ferrooaotus wislizenii 1 2.2 - 


Fagonia califoralca 2 0.7 - 

Total 110 







Salea mollis 

Dalea parryi 

DltaxlB neomezleana 




Peotls papposa 

Perityle emoryi

Phaseolus fillformis 

Tideatromla lanuginosa 


Total species in quadrats 26 

Total speoies in stands 2?

on Baja California, the adjacent islands on the west side 

of the Gulf, and some also on the Sonoran ooast toward the 

head of the Gulf, north of Isla Tiburon. 

The thomscrub and thornsorub-like areas oontain 

populations whioh are northern outliers from subtropical 

regions to the south. The greatest concentration of these 

2 67 

elements ooours in the southeast foothills and canyon-valleys 

of Sierra Kunkaak* 

Several plant speoies introduced to the New World 

in post-Columbian times have reached the interior of the 

island and are now well established* 

The terrestrial vertebrate fauna is by and large 

not differentiated from the adjacent mainland* A reoently 

discovered speoies of Eohlnocereus is the only endemio 

plant•

ISLA SAN ESTEBAN 

Isla San Esteban Ilea about 12 kms. south of the 

southwest shore of Isla Tlburon* Gentry (1949, P« 95) 

provides the following suoolnot description* 

San Esteban lies in mld-ohannel In the middle of 

the gulf region off Tlburon Island. Quadrangular 

in shape, it embraces about 35 square kilometers 

of rugged land with a top elevation of 

meters at the south end* Voloanio in origin, it 

has "sooriae-oovered slopes and muoh breooia" 

(Johnston 192^*95^)• It is shored mostly with 

high vertical cliffs, but on the southeast is a 

pebble beaoh and a broad valley above the beaoh 

provides ready ingress* No souroe of fresh water 

has been reported* 

The island is not entirely voloanio in origin and seems to 

268 

be geologioally related to Isla Angel de la Guarda and with 

a similar origin (Bunsk and Fisher, 196*0 * 

A horseshoe-shaped series of steep mountains sur 

round the central valley (Figs* 59 and 60)* Its floodplain 

is full of transported rook and gravel heaped into uneven 

ridges and traversed by shallow washes* Interiorly the 

valley narrows into a number of small and rather short 

rugged canyons. 

The island is arid and summer precipitation in 

some years is drastically reduced or even absent* In the 

fall of 1963 the oondition of the vegetation indioated 

that there had been little or no summer-fall rainfall*

Figure 59* Aerial view of Isla San Este'ban; looking south 

east. West shore on right*

Figure 60• Aerial view of Isla San Estebanj looking west. 

Central valley (oenter); rock jutting into sea 

is El Monumento (left foreground)*

270

However, In August of 1961* the island had apparently 

received sufficient rainfall to produce verdant summer 

vegetation (J* R. Dixon, personal communication and review 

of Kodaohrome transparencies)• The oentral valley, shel 

tered by the surrounding mountains« appears to contain a 

271 

"heat sink" due to intense insolation and re-radiation from 

the partially "barren rook slopes, and looal island heating 

may oontrlhute to the observed aridity* It is assumed that 

the island is frost-free. 

Seven species of reptiles are known from Isla San 

Esteban (Appendix B) • The following are endemios 

Crotalus molossus estebanensls 

enemafphorus tigrls estcbanensls 

Mastlcophus blllneatus slevini^^ 

Sauromalus varlus 

Uta stansBurlana"klauberl 

Hvpslglena torauata venusta is principally a Baja California 

subspeoies while Phvllodactvlua xantl is relatively wide 

spread in the northern part of the Gulf* Thus while at 

least one of the speoies shows greater affinity with Baja 

California most of the herpetofauna indicates closest rela 

tionship with Isla Tiburon and the Sonoran mainland (see 

Lowe, 1955i Lowe and Norris, 1955)* The scant evidenoe 

now available, the differential phyllogenetio divergences, 

and the various biogeographioal patterns indioate a separate 

history for each of these populations*

The endemio Peromvsous stephanl is the only native 

land mammal occurring on the island. A population of 

Battus rattus is well established (Burt, 1938), and my 

observations indicate its continued existence, at least 

near the east shore of the island* It apparently does 

not compete with the Peromvsous (Burt, 1938)* That Battus 

was able to beoome established seems to be due in part to 

272 

an unoooupled niohe and possibly the laok of oertain poten 

tial predators. Battus is not known to have beoome estab 

lished elsewhere in the Sonoran Desert away from human 

habitation. 

Van Bossem (19^5) considered the avifauna of Isla 

San Esteban to be more olosely related to that of Baja 

California (San Laoan avifauna area) than Isla Tiburon and 

the Sonoran coast, but as pointed out by Lowe (1955» P* 3^1)» 

"The avifauna is not well enough known to arrive at any 

satisfactory conclusion as to its affinities, . . . ." 

Herblvors on San Esteban are limited to the two 

rodents and the large ohuokwalla, Sauromalus varlus. which 

is abundant throughout the island. Favorite food plants 

of the ohuokwalla include Pitaxis lanoeolata. Hibiscus 

denudatu8i Trlxls califomlous. and cactus flowers. In 

dry seasons these plants (exoept for the oaoti) are often 

grazed to mere nubbins by the ohuokwallas, yet they are 

very oommon. Several mammals prevalent on Isla Tiburon,

£.•£•* Caula. Dlpodomys. Lepus. Neotoma, OdoooIleus, and 

Peropnaathus. are not present on San Esteban and the effect 

upon the vegetation, although not measureable( must cer 

tainly be significant. 

Prior to the decade of about i860 a small band of 

273 

seafaring Seri Indians lived on San Esteban (Griffen, 1959; 

Moaer, 1963)* They had no agriculture and probably did not 

spend the entire year there (Moaer, 1963). Agave dentlens, 

whioh is common on the island, provided them with an import 

ant source of sustenance (Moser, 1963) and has likewise been 

utilized by non-Serl Mexicans, but only to a minor extent* 

Senor Jesus Morales, an elderly Seri now living at Desem- 

boque, Sonora, tells of the time when he was a boy, of 

expeditions to San Esteban from Tiburon for the purpose 

of gathering Agave. The base of the plant was roasted in 

the same manner oommonly employed elsewhere in Mexico and 

large pits for suoh use are still visible on the island* 

It is rumored that goats were onoe introduced but 

that the project failed because Seris captured and 

slaughtered them for food, and thereby saved the vegetation 

from sure ruination (E. Moser, personal communication)* 

Plora and Phytogeograohy.—Eighty-eight species of 

vasoular plants are reported from San Esteban in the present 

work (Appendix A) and I estimate additional speoles. 

There are no phylogenetioally related series of species

and not more than two species ooour within any one genus. 

27^ 

The 88 speoies are distributed among different families* 

The greatest number of speoies per family ooours in the 

Caotaceae, Composltae, Gramlneae* and Leguminosae. Speoies 

of the latter three families play only a minor role in the 

total vegetation while the Caotaoeae form a oonspiouous and 

dominant element in the landsoape (Figs* 6l and 62)« 

Indications of endemism are shown only by Carlo- 

wrlahtla callfornloa and a yet unidentified Qpuntla 

(Cvllndropuntlaand a Mammlllarla. but they are too 

poorly known to allow conoluslons* Thus with suoh possible 

exceptions neither dlstanoe nor time of isolation has been 

sufficient to allow endemic forms to evolve. 

Host of the speoies are oommon to both shores of 

the Gulf* However> the general physiognomy of the vege 

tation and the distributional patterns of many of the 

speoies show relationship with the arid regions of the 

west side of the Gulft 

Agave dentiens 

Arpemone subintegrlfolla 

Chiorla^brandegeel 

Cryptantha fastlalata 

Echinooereus^grandls 

Lvrooarpa linear1folia 

Mftimniiiaria of, angelensls 

Slderoxvlon Ieuoophyllum 

1. This Cyllndropuntla was relegated to Qpuntla 

versicolor by Gentry {19^9) but it is at least subspeclfioally 

distinct*

Figure 6l. Lower portion of central valley, Isla San 

Esteban; looking southeast. Atrlplex poly- 

oarpa. Jatropha ouneata. Maohaerooereus gum- 

moaua. and Paehyoereus prlnglel.

275

Figure 62. Eohlnocereus grandls on Isla San Esteban* 

Buler calibrated In feet and tenths*

276

Species with similar ranges but also occurring at the head 

277 

of the Gulf inolude Pranserla lllclfolla. Nenocladus glandu- 

liferust and Petalonvx linearis* The distributional affin 

ities with Isla Tlburon are generally with its arid west 

rather than south coast, and thus the relationship appears 

to be correlated more with climatic similarity than spatial 

distance. 

The following twenty-five species of ephemerals, 

comprising nearly 30J$ of the total flora, are presents 

Amaranthus watsonll Euphorbia polyoarpa 

Antirrhinum oyathlferum Luplnus "ap. 

Arlstlda adscenslonls Mentzella adhaerans 

Boerhaavla ap. Muhlenbergla mlcrosperma 

Bouteloua arlstldoldes Nemaoladus glapdul1ferua 

Bouteloua barbata Panlcum arlzonious 

Camlsslona cardTophylla Parletarla florldana 

Cryptantha fastlglata Per1tyle"cal1foraloa 

Cryptantha marltlma Perltyle emoryl 

Cenohrus palmerl Petalonyx linearis 

Phaseolua flllformls 

plants is surprisingly low* Some of the few truly common 

ones arex 


SnElrrhlnum oyathlferum 

Arlstlda ad'soenslonls 



Dalea parryl 

Sympetefela rupestria 

Vaseyanthus insularIs 

The density of most of the ephemeral and herbaceous 

The following trends were noted during winter and 

spring seasons in several different years: (1) Ephemerals

are generally absent over most of the south-faeing slopes 

but are sometimes present with up to coverage; (2) 

toward higher elevations and on north- and east-facing 

slopes herbaoeous plants may produoe nearly half of the 

plant cover, but these often tend to be perennial rather 

than ephemeral speoles; (3) looallzed colonies along the 

main floodplain and along the rooky east beach may produoe 

up to 80# ooverage* but in general they are very sparse* 

The gap between short-lived typical ephemerals, 

e.g., Antirrhinum oyathlferum. Arlstlda adsoenslonls. 

Cenohrus palmer1. and Perltyle emoryl. and the perennial 

278 

habit is represented here by various intermediate patterns. 

Cryptantha fastlglata is commonly a "long-lived annual* 1 

(see Johnston, 1924, p. 11^8) and doubtfully perennial here. 

Euphorbia polycarpa. Dalea parryl. Petalonyx linearis, and 

Vaseyanthus insularIs flower during their first season of 

growth and a small percentage sometimes survives to become 

perennials. Euphorbia pedlcullfera. frequently developing 

into a perennial elsewhere in the Gulf, has been found 

solely as an ephemeral on San Esteban. Most of these 

species have small leaves and quickly develop deep tap 

roots, and when existing as ephemeral (or during their 

first season) they continue to flower and bear foliage 

longer into the spring drought than the strictly ephemeral 

species.

Growth-forms.—Only a few species present on the 

island develop an arborescent habit, e.g., Fleas palmer1. 

Olneya tesota. and Paohyoereus prlnglel. Paohyoereus. the 

largest, generally reaches a maximum height of 6 to 7*5 a* 

and the tallest Olneya measured 4.1 m. in height* Both 

Paohycereus and Olneya reach maximum development along the 

valley floodplain where they are common.. FIQUB palmerl is 

unoommon on San Esteban and is generally restricted to 

steep sea cliffs where it usually remains a facultatively 

dwarfed shrub and only rarely becomes a small tree 4 to 5 

high. Slderoxylon leucophylla. occurring at the top of the 

island, may become a small tree. Bursera microphylla has a 

well developed trunk but soaroely becomes arborescent on 

San Esteban. 

The vegetation of the island consists largely of 

shrubby plants representing approximately 65$ of the flora. 

Large vines are lacking and vining, trailing, or semi- 

vining plants are few, small, and relatively inconspicuous, 

e.g., Janusla gracilis. Passiflora arida, Phaseolus flll- 

forml3. and Vaseyanthus insularls. Forms with tuberous 

roots and bulbs are unknown from the island. 

Pinnate-leaved species are represented by Bursera 

mlcrophylla and the legumes, and comprise nearly 10% of 

the flora. The remaining speoies have simple leaves or 

are aphyllous. Most of the leaf-bearing perennials are

drought-deciduous and other than the suooulents there are 

only a few with an evergreen or partially evergreen habit, 

e.g., Peuoephyllum schottll and Atrlplex polvoarpa. 

Several species may be tardily drought-deciduous but ulti 

mately become leafless or essentially so during severe 

280 

drought, e.£., Flous palmeri, Olneya tesota. and Slamondsla 

ohlnensls. Franserla lllolfolla shows an interesting adap 

tation whereby the dead leaves turn whitish and persist on 

the stems through dry seasons, and thus provide shade to 

the rest of the plant. 

Suooulent plants form a very evident part of the 

landscape and are oommon and widespread. The large stem 

succulents (columnar oactl and oholla) reach greatest 

development along the valley floodplaln while the smaller 

succulents, e.g., Eohlnooereus grandis. Agave dentlens. 

and llarla of. angelensls. are most abundant on the 

rooky slopes. In general, maximum suooulent growth occurs 

on east-facing slopes, diminishes with south and west 

exposure, and is mostly absent from north slopes. 

Shore and Sea Cliffs.—Sea cliffs and short rooky 

beaches preclude all but a rarlfied shore vegetation of 

semi-littoral species, e.g., Atrlplex barolayana« Suaeda 

torreyana. and Vaseyanthus lnsularls. These occur along 

rook beaohes in front of arroyos (Fig. 63) but suoh habit 

ats are few and of limited scope.

Figure 63. East-central shore of Isla San Esteban, lower 

end of central valley; looking northward* 

South shore of Isla Tlburon in background. 

Agave dentlens. Eohlnooereus grandls. Maohaero- 

oereus CT"»"OSUS (extreme right), and Paohy- 

oereus nrlnglel.

-8s —^ 

*" 

1& 

ro 

00

Characteristic sea cliff speoies include Flcus 

palmerl. Hofmelsteria fasoloulata. Hofmelsterla lapha- 

mioides. and Svmpetelela rupestris. 

Floodplain.—Desertscrub along the main valley 

floodplain shows rloher growth than along the adjaoent 

slopes but is relatively xerophytio (Plot 51a Table 52» 

Figs. 63 and 64)• In general the vegetation beoomes 

282 

slightly rloher toward the south side of the valley (north 

exposure) and farther inland than it is at the north side 

of the valley (south exposure) and toward the shore* Plot 

51 was located in the middle of the valley at approximately 

1 km. inland. Common elements in the landscape include 

desert shrubs, columnar oacti, oholla, and various smaller 

succulents. Large succulents (oacti) reach maximum develop 

ment along the floodplain and together with Jatropha ouneata 

form dominant elements. It is interesting to note that in 

most of the other regions of the Gulf Coast of Sonora 

Jatropha ouneata and large oaoti are usually absent or 

rare along floodplains. Olneva tesota and Bursera micro- 

phylla do not reaoh as great a size as on Isla Tiburon and 

the mainland and here remain as dwarf trees or large shrubs. 

Plant cover is oa. 50#. A total of 29 speoies was present 

of which 27 were within the limits of the 0.1 ha. quadrat. 

Slopes. —Desert shrubs and succulents form a rela 

tively thin cover over the rugged and rooky mountain slopes

TABLE 52 

283 

PLOT 51- ISLA SAN ESTEBAN, FLOODPLAIN CA. 3/4 KM. NORTH- 

VEST OF EL MONUMENTO, EAST-CENTRAL SIDE OF ISLAND, CA. 5 M. 

ELEV. NEARLY LEVEL. SANDY-GRAVEL SOIL AND HUCH TRANS 

PORTED ROCK. COVERAGE CA. 50%. 26 FEBRUARY 1965 

Number 

Speoies (0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Paohyoereus prluglel 5 24.5 21.5 



Vlsoalnoa genioulata 4 8.7 7.8 


Atamlsquea emarginata - 8.1 - 


Maohaerooereus gummosus - 7.2 - 

Slmraondsla chlnensls 13 6.6 5.4 

Stegnosperma halimlfollum 4 6.4 5.4 

Prosopis torreyana 3 6.1 - 

Atrlplex polyoarpa 56 5.6 5.0 

Opuntla (Cyllndropuntla) 

sp. l 5.3 4.7 

Lyolum sp. 5 4.2 4.2 

Solatium hlndslanum 5 4.1 - 

Dltaxls lanoeolata 33 3.6 2.6 

Agave dentiens mm 3.3 mm 

Beloperone oallfomloa 1 2.7 - 

Trills oallfomloa 5 2.6 2.0 

Franserla lllolfolla 11 2.5 2.3 

Hoffmanseggla intricata 17 2.1 1.8 

Carlowrlghtla oallfomloa 15 1.6 1.5 

Hlblsous denudatus 2 1.4 1.4


Eohlnooereus grandis 2 1*2 

Mammillarla of. angelensls 6 0.6 

Total 2^3 


Amaranthus watsonil 






28*f

Figure 6k* Central valley, Isla San Esteban; looking 

west. Agave dentlens and Paohyoereus 

jgrlnglel.

285

286 

of the island* Generally the density, coverage, and number 

of speoies inorease toward higher elevations and on north 

and east-facing slopes( and diminish onto south and west 

slopes and lower elevations. In general plant oover thins 

on steeper slopes and is largely absent from the rock slides 

whioh occur throughout the island. Rooky mesa-like ridge- 

crests likewise may be partially barren* 

A representative east slope oommunity was ohosen 

on the rooky slopes above the south side of the central 

valley (Plot 52, Table 53» foreground of Pig. 63)• The 

dominant elements here include small desert shrubs, suf- 

frutesoent species, and small suoculents. These include 

the following, listed in approximate order of maximum 

coverage: 


Solanum""hlndslanum 

Agave (Tentlens 

Eohlnocereus grandla 

Atriplex barolayana 

liar la of. anaelensls 

Paohyoereus prlraclel exceeds the height of the next tallest 

speoies by several times but it is localized and not common. 

Twenty-eight speoies were present in the stand and 2b in the 

quadrat• 

Plant communities on south-facing slopes are rela 

tively simple and sparse (Plot 53t Table 5^» background of 

Fig. 63). Plot 53 was ohosen on the slopes above the north

TABLE 53 

287 

PLOT 52. ISLA SAN ESTEBAN, CA. 1/4 KM. WEST (INLAND) OF EL 

MONUMENTO, SOUTHEAST SIDE OP ISLAND, CA. 50 M. ELEV. EAST 

EXPOSURE, 80-110°, SLOPE 22%. SHALLOW SOIL, VOLCANIC BOCK. 

COVEHAGE CA. 40£. 27 FEBRUARY 1965 

Maximum Mean 



Paohyoereus prlnglei 1 17.0 - 

Colubrina glabra - 5.8 - 

Maohaerooereus gummosus 4 5.1 4.6 

Desmanthus frutloosus 6 9 3.6 

Jatropha ouneata 89 **.7 3.0 

Bursera miorophylla 2 *.5 4.0 

Condalla globosa - *.3 - 

Opuntla versicolor If 4.3 3.9 

Prosopls torreyana 16 4.2 3.6 

Slmmondsla chinensis 21 3.^ 2.8 

Solanum hludslanum 123 3.2 2.8 

Agave dentlens 95 3.0 2.3 

Vlgulera deltoldea 8 2.8 2.4 

Horsfordla newberryl - 2.7 - 

Trlxls oallfornloa if 2.3 1.8 

Atrlplex polyoarpa 1 2.2 mm 


Atrlplex barolayana 252 1.6 1.2 

Eohlnooereus grandla 46 1.6 1.2 

Hibiscus denudatus **6 1.6 1.4 

Sphaeralcea sp. 20 1.5 1.2 

Hoffmanseggla lntrloata 9 1.2 0.9 

Porophyllum orasslfolium - 0.8 - 

Mammillaria of. angelensis 77 0.4 0.4 

Total 

1020


Aristida adsoenslonis 

Boerhaavla ap* 




Total speoies in quadrats 2k 


TABLE 5k 

PLOT 53* ISLA SAN ESTEBAN, CA* 1 KM. INLAND (WEST) FROM 

EAST-CENTRAL SHORE, CA. 60-7(5""K. ELEV. SOUTH EXPOSURE, 

190-200°, SLOPE 3ljb. SCORIAE AND SHALLOW SOIL* COVERAGE 

CA. 15J6. 27 FEBRUARY 1965 

Maximum Mean 



Paohyoereus prlnglel 2 17.2 13.5 


Asoleplas albloans 14 6.2 5-7 

Jatropha cuneata 73 b.6 3.3 

Bursera mlorophylla 3 *•3 - 

Opuntla versicolor 7 Jt.l 3.7 

Atrlplex polyoarpa 1 3.7 - 

Agave dentlens ^5 2-7 2.5 

Trlxls oallfomloa 5 1*8 0.9 


Eehlnooereus grandis 50 0*9 0.6 

Mammillarla of* angelensis 138 0.^ OA 

Total 701 


Aristlda adsoenslonls 


Dalea parryl 

Dltails neomexloana 

Total speoles In quadrats 16 

Total speoles In stands 16 

289

side of the valley floodplain opposite Plot 52• Plant 

cover is 15% with only 16 speoies present* As on the east 

slopes the maximum height of plants below Pachyoereus 

pringle1 seldom exoeeds 1.8 to 2 m* and the majority of 

the plant coverage is made up of much lower growth* The 

most oommon and oonspiouous speoies are Agave dentlens. 

Hlblsoua denudatus. Jatropha ouneata, and Mammillaria of. 

angelensls* 

Toward the top and north side of the island the 

vegetation becomes slightly denser and less xerophytio 

speoies begin to appear» yet desert shrubs and suooulents 

290 

oocur to peak elevation* Agave dentlens exhibits an inter 

esting elevatlonal variation with more xerophytio forms, 

£•£•• gray leaves and numerous stout marginal spines, at 

lower elevations and an lnorease in less xerophytio forms 

at higher elevations, e.g., greener leaves and spineless 

margins* Species confined to higher elevations Includes 

Acalypha oallfornloa 

Argemone sublntegrlfolia 

BursereT"hindslana 

Euphorbia mlsera 

Galvezla .lunoea 

Lvrooarpa linear1folia 

slderoxyTon leuoophyllum 

Several speoies are common at higher elevations and ooour 

again along the valley floor but are generally absent from 

the intervening arid slopes, e.g., Chioris brandegeeli 

Cryptantha fastiglata* and Nicotlana trlgonophylla *

Summary. —Vegetation on Xsla San Esteban consists 

of xerophytio desertsorub with suooulents forming a con 

spicuous element of the landscape. Two major phytogeo- 

graphio patterns are evident! (1) Speoles showing rela 

tionship primarily with arid northern regions of the Gulf 

including the northern Gulf Coast of Baja California and 

the adjacent islands of the west side of the Gulft and (2) 

291 

speoles whloh are common to both sides of the Gulf and Isla 

Tlburon and oonstitute the majority of the flora. Endemism, 

largely at or near the subspeoifio level, ooours among the 

terrestrial vertebrates and is indicated for several oaoti.

ISM DATIL 

This island lies at the south end of a partially 

submerged peninsula extending southward from the southeast 

shore of Isla Tiburon (Fig. 65). The peninsula is roughly 

5 kms. long with its emergent portions consisting of Isla 

Datil at the south end and Isla Cholludo between Datil and 

292 

Tiburon. Reefs oonneoting the islands are evident and both 

islands appear to be rather reoent fragmentations from 

Tiburon (Lowe, 1955)* 

Datil is composed of metamorphio rooks which include 

quartz diorite (Anderson, 1950) and shale. Similar rook of 

pre-voloanio age ooours on portions of the opposite south 

east ooast of Isla Tiburon (Anderson, 1950) and may also 

underlie the volcanic rooks of Isla Cholludo. 

The island is locally oalled Isla Datil and the map 

names Isla Turners or Turners Island are unknown to the 

looal fishermen. Datil is the Spanish word for the date 

palm (Phoenix daotyllfera) and in northern Mexloo it is 

also employed for the yuooa, e.g., Yuoca arlzonlca. Here 

it refers to the small oentury plant (Agave subsimplex) 

whioh is abundant on the island. 

The Island is formed of a narrow north-south 

oriented mountain with a prominent ridge running along 

its axis. The peak elevation is 180 m. (Tamayo, 19W.

Figure 65. Aerial view of Isla Datll, Isla Cholludo, 

and the south end of Isla Ti"bur011.

IW.v 

293

Tamayo (19^9) gives the island's maximum dimensions as 

1200 m. in length and 800 m. in width, thus the total area 

294 

should be less than 1 sq* km* The topography is very rugged 

and offers a wide range of habitats* There are a few small 

rook beaohes but most of the shoreline oonsists of high sea 

cliffs. At the northeast side of the island several small 

oanyons empty into short beaohes and provide ready aooess 

to the Island* The northwest side is somewhat steeper but 

also allows comparatively easy ingress* Datil is rooky and 

steep throughout and the soil is generally shallow* Can 

yons or arroyos fall steeply and are rook-strewn and with 

out sandy streamways or washes* The general physiognomy 

of the island Is vaguely similar to Isla San Pedro Holasoo 

but Datil differs from Nolasoo by its smaller size, rela 

tively shallow channel, and generally deeper soil profile. 

The parent rook materials and vegetation of the island 

appear to be very different* 

There are no weather reoords but my observations 

indicate that Datil and Cholludo reoelve somewhat greater 

summer-fall rainfall than the adjacent mainland, £•£*» 

in the vicinity of Bah£a Kino, and Isla San Esteban* This 

may be due to the orographio effects of 31erra Kunkaak in 

the southeastern part of Isla Tiburon and the island 

itself* Winds tend to be greatly reduced in the vicinity 

of Islas Datil and Cholludo and the adjaoent south shore

of Tiburon. It la assumed that the Island Is frost-free. 

Maritime oondltlons further provide favorable conditions 

for plant growth* 

Burt (1932, 1938) reports three speoies of land 

mammals, representing endemic taxa, from the island: 

Neotoma varla. Perognathus penicillatus minimus. and 

Peromysous collatus. A recent oolleotion of rodents made 

by Mr. Osoar Soule and myself indloates a need for taxo- 

nomlo revision of the mammalian fauna of the island* 

Peromysous oollatus, described from a single specimen, 

appears to be oonspeoifio with Peromysous eremlous and is 

perhaps not distinct from Peromysous eremlous tlburonensls 

295 

from Isla Tiburon and the vicinity of 5ah£a Kino (Mr* James 

Patton, personal communication) • In addition we obtained 

specimens of Perognathus lntermedlus which will be described 

as a new subspecies by Mr* Patton. 

At least six speoies of reptiles probably occur on 

the island. An endemic dwarf raoe of Crotalus atrox (Lowe, 

1955) is present. Other reptilian species do not appear to 

be distinct and have relatively extensive geographic ranges 

Including Isla Tiburon: Gophorus agassizl, Mastloophis 

flagellum. and Uta stansburlana. Mastloophls Is evidenced 

by two shed skins. Phyllodaotylus xantl and Ctenosaura 

hemllopha. whioh are common on nearby Isla Cholludo, may 

reasonably be expected to occur on Datil.

Flora and Phytogeography.—-Isla Datll supports a 

296 

comparatively rich flora In proportion to Its size. Eighty- 

three speoles are reported In the present work (Appendix A) 

and approximately 10# more are predicted to oocur on the 

Island. Most of these speoles are present on neighboring 

land masses but there are also a number of Interesting 

extra-llmltal populations. 

Calllandra califomlca Is common on protected north- 

and east-facing slopes and along arroyos on the east side of 

the Island. It is otherwise known with certainty only from 

Baja California. Cnldoscolus palmerl Is another Gulf of 

California endemlo and Is elsewhere known only from Baja 

California and the Guaymas region. Coldenla oanesoens and 

Euphorbia ml sera are northern elements and the populations 

here are southeastern outliers. Coldenla oanesoens Is not 

known elsewhere In the Gulf Coast of Sonora. There Is an 

extensive population of Mammlllarla whloh Is either oon- 

speclflo with Mammlllarla dlolca or very closely related 

to It. The same taxon occurs on Cholludo but It has not 

been found anywhere else In Sonora. It Is an eastern dis 

junct from the Mammlllarla dloloa whloh ranges nearly 

through Baja California and extends Into southern Cali 

fornia. 

Families with the greatest number of species on the 

Island are Caotaoeae, Composltae, Euphorblaoeae, and

Leguminosae. There are no endemic taxa although the 

Mammlllarla whloh also occurs on Cholludo may be a sub 

species endemic to the two islands. 

297 

Growth-forms *—The landscape of Isla Datil is domi 

nated by desert shrub communities. Arborescent species 

inolude only the columnar oacti and rare specimens of Flcus 

palmerl which may develop into small trees. 

Succulent plants are oommon but are markedly less 

prevalent than on Isla Cholludo. Those on Datil include 

Agave subsImplex. Hofmelsterla fasclculata. and nine species 

of cacti. The presence of rodent populations and difference 

in soils and slope exposure may contribute to such marked 

vegetational differences on these neighboring islands. 

During dry seasons the vegetation appears brown and 

parched due to the preponderance of drought-deciduous 

desertscrub species. Vining plants are few and poorly 

developed and are usually oonfined to sheltered canyons: 

Cardlospermum corlndum 

Janusla oallfornloa 



Tragla amblyodonta 

Summer-fall ephemerals include 20 species comprising 

of the total flora. The winter-spring ephemerals are 

unknown although twelve of the summer-fall speoles char 

acteristically occur again with winter-spring rains and are 

indioated in the following list by an asterisk. Summer-fall

# . 

ephemerals on Datil are: 

Alllonla lncarnata Euphorbia pcdlcullffcra* 

Amaranthus fimbriates Euphorbia petrloa* 

Amaranthus vataonll^ Euphorbia polycarpa* 

Antirrhinum cyathlferum* Kallstroemla oallfornloa 

Boerhaavlaof. ereota Mentzella adhaerans* 

Bouteloua""aHatidoldes # Perltyle*""emoryl* 

Coreoearpua of. arlzonlous Phaaeolus flllformls* 

galea parryl^ Setarla lletanannll 

Daturadlscolor* Svmpetelela rupeatrls* 

Dltaxla neomexlcana* unidentified Gramineae 

Habitats.—In general, vegetation on the east side 

of the island is denser and more brushy than that of the 

west side. Elevational gradients in the vegetation are 

very weakly developed. 

The riohest vegetation occurs along the canyons of 

298 

the east side of the island. East- and north-facing canyon 

slopes, and the canyon floors, support relatively dense 

desertscrub (Fig. 66). Plant coverage on such sites la 

seldom less than 50$ and commonly reaohes 80$. The richest 

communities occur on north-facing slopes near the summit on 

the east side where 32 species were found in a 0.1 ha. quad 

rat with approximately 3^ species in the stand. However, 

the major part of the island is more xeric and supports 

fewer species per area or community. Characteristic species 

on north- and east-facing canyon slopes and canyon bottoms 

on the east side are listed belowt 

Aoalypha califoraloa Euphorbia mlsera 

Agave subslmplex Fouqulerla splenaens 

ArrlPlex polycarpa Franserlailvarlcata 

Bebbla .luncea Hibiscus"denudatus 

Berglnla vlrgata Janusla""oallfornloa

SV-BS 

299

Buraera hlndslana Janusla gracilis 

Buraera mlorophylla 

" Kramerla grayl 

Calllandra oallfornloa Llppla palmer 

Cardlospermum oorlndum Lyolum ap» 

Cnldoaoolua palmerl Manmlllarla of, dloloa 

Colubrlna glabra Qpuntla leptooaulls 

Condalla~globoaa Perltyle emoryl 

Condalla* lvololdea Phaulothamnua Phaulothanmua a apineaoens 

Dalea parryl Slmaondali 

Slmaondala Chilians la 

stegnoapea 

Pitaxia lanoeolata Sympeteieia rupeatria 

Enoella farlnoaa Tragla amblyodonta 

Euphorbia pedlcullfera Vlgulera deltold"ea 

Deamanthua rrutlcoaus stegnoaperaa hallalfollum 

Various oaoti and xerophytic desert ahruba are preaent but 

in greatly reduoed numbers as compared with the more arid 

300 

south slopes and the west side of the island, &•£•» AtrlPlex 

polyoarpa. Lemalreooereus thurberl. Jatropha ouneata. and 

Bebbla .lunoea. 

On the south* and west-facing slopes oolumnar oaoti, 

Jatropha ouneata. Fouaulerla splendens and other xerophytio 

desert shrubs oonstitute the major oover. Plant coverage on 

these arid slopes reaohes 20 to 35#t but may be as little as 

15%, Ephemeral oover is sparser and the individual plants 

shorter-lived than on north and east slopes* Characteristic 

major perennials of south- and west-faoing slopes includei 

Atrlplex polyoarpa 

Bebbla .lunoea 

Buraera mlorophylla 

Coldenla oanesoens 

Pit axis lanoeolata* 


EuphorblsTpolyoarpa 

Fagonla oallfornloa 

Boffmanw^la lntrToata 

Tafcropha ouneata 

Lemalreooereus thurberl 

Paohyoereua pringle1 

Slmmondsla ohinensls

Summary.—Iala Datil supports a surprisingly rloh 

flora with a number of unusual extralimltal populations. 

A comparatively rloh terrestrial vertebrate fauna is indi- 

oated among which there are several endemics. Much of the 

301 

island is covered with dense and brushy desertsorub. Sparse 

and xerophytic communities are generally restricted to rook 

slides and arid exposed portions of the west side. The 

flora and fauna are olosely related to those of the neigh 

boring south shore of Isla Tlburon and Isla Cholludo; how 

ever, the vegetation is distinctive. The richness of the 

biota appears to result from looally favorable and unique 

environmental conditions as well as spatial and temporal 

closeness to a larger land mass (Isla Tiburon).

ISLA. CHOLLUDO 

Isla Cholludo (Figs* 65 and 67) Is a tiny rook 

Island situated between Isla Datll and Isla Tlburon along 

a sunken peninsula which Interoonneots the three islands. 

Both smaller islands appear to be relatively recent frag 

302 

mentations of the parent Isla Tlburon (Iowe, 1955)* Tamayo 

(191*9) gives the name as Isla Lobos but this name is looally 

unknown to the people in Sonora. The area of the island is 

roughly estimated to be 1/2 sq* km* The south side falls 

away abruptly into high cliffs (Fig* 67) where numerous sea 

birds roost* From the south ridge-orest, estimated to be 

75 to 100 m* elevation, the rest of the island quiokly 

slopes down to the north shore. Most of the island's sur 

face Is encompassed in the northerly faolng slope* Approxi 

mately half of the slope faces north-northwest and the other 

half north-northeast* There are no major arroyos and 

although the slope is steep and rooky its surfaoe is con 

tinuous* The surfaoe rook appears to be voloanlo* 

On Cholludo, as on Datll, deslooatlng winds, so 

prevalent in the Gulf region, are greatly reduced thereby 

contributing to a relatively high humidity and a con 

siderable amelioration of temperature extremes* Also, as 

with Isla Datll, preliminary observations indioate that 

summer—fall precipitation may be slightly greater or more 

regular than In many nearby regions (see p. 294).

-Figure 67 • East side of Isla Cholludo*

303

The terrestrial vertebrate fauna oonsists of only 

two speoies of lizards: Ctenosaurus hemilophus and 

Phrllodaotylus xanti. Both are oommon on the island* 

Rodents seem to be absent and trapping efforts proved 

negative• 

Twenty-six speoies of vascular plants are present 

(Appendix A), the highest number of speoies in proportion 

to island size of any of the Sonoran islands* I do not 

expeot that more than a few speoies remain undisoovered 

on the island^ and these will probably be winter-spring 

ephemerals. Locally favorable environmental conditions 

and close proximity to larger vegetated land masses seem 

to be major faotors contributing to the comparative rich 

304 

ness of the flora. All of the speoies ooour on the neigh 

boring islands of Tiburon and Datil except Carnegiea 

gigaptea which is absent from Datil. Floristio similarity 

with neighboring land masses is explainable by their olose 

proximity (Fig. 68). 

Vegetation.—Isla Cholludo is aptly named as it 

supports a most formidable and scarcely penetrable cactus 

forest (Figs. 67, 68, 69, and 70) unlike the neighboring 

islands and mainland. Plant cover over most of the island 

is estimated at 70 to 80# of the surface. Agave subslmplex 

is abundant over the eastern half, which faoes north- 

northeast, but it is absent from the western part with a

Figure 66. Looking north from Isla Cholludo toward the 

south shore of Isla Tlburon.

K-> **> -fj < ^ v 4 

Mil 

305

Figure 69 • Northeast side of Isla Cholludo. Lenalreo- 

oereus thurberl. Qpuntla fulglda. and Pachy- 

oereus prlnglel»

306

Figure 70. Charaoteristio suooulent growth on northeast 

side of Isla Cholludo. Lenalreooereus thur- 

beri, Qpuntla fulglda. and Paohyoereus prlnglel.

north-northwest exposure. Succulent species dominate the 

308 

vegetation and Impart a somewhat evergreen and non-seasonal 

aspect to the landscape. The three larger cacti, i.»«*» 

Lemalreocereus thurberl. Qpuntla fulglda. and Pachycereus 

prlnglel. contribute the majority of the total biomass and 

coverage on the island* Non-succulent leaf-bearing plants 

play a decidedly minor role, and larger-leaved species, e•£•, 

Flcus palmer! and Bursera hlndsiana. are rare. There are a 

few woody shrubs, e.£.» Colubrlna glabra. Atamlsquea emargln- 

ata. Lyolum sp., Olneya tesota. Trees other than the col 

umnar cacti are absent. Most of the leaf-bearing species 

are drought-deciduous and have simple and entire or nearly 

entire margins. Bursera hlndsiana and Olneya tesota are 

the only compound-leaved species on the island; vines have 

not been found. 

Six species of ephemerals, constituting nearly 25^ 

of the total flora, are present: 


Bouteloua arTs^ldoldes 

Paulcum arlzonlcum 

Pectls palmerl 


Sympetelela rup'estrls 

Conspicuously absent among the present collections 

of herbaceous forbs and ephemerals are several species com 

mon on the neighboring islands. These lnoludet 

Alllonla lnoarnata 



Cenohrus palmerl Vaseyanthus InsularIs

The locally unique physiognomy of the vegetation 

seems due to the relatively different biotio and environ 

mental conditions. Similar-appearing oactus-oovered 

islands of voloanio origin occur in Guaymas harbor, where 

maritime conditions and calm weather likewise prevail and 

it would be interesting to know if there is a correspond* 

ing absence of rodents. 

Summary.--The vegetation of Isla Cholludo consists 

of almost uniformly dense and nearly impenetrable caotus- 

dominated desertserub* As with Isla Datil, the flora is 

comparatively rioh for the small size of the island. Host 

of the species are oommon to the adjacent south coast of 

Isla Tiburon and all but Carneglea gjgantea occur also on 

Datil. The vegetation is unique for this region but it 

309 

resembles some of the small caotus-covered isles of similar 

size in Guaymas harbor. Terrestrial mammals appear to be 

absent and two species of lizards constitute the known 

terrestrial vertebrate fauna.

INFERNILLO REGION 

310 

The Infernlllo region extends from Cerro Tepopa In 

the north to Cerro Prleto in the south and is delimited on 

the east by the Sierra Serl range and on the west by the 

Infernlllo channel (Fig. 71)• A vast west-facing bajada 

about 3 to 5 kms. wide encompasses most of the area between 

the shore and the Sierra Serl. 

The vegetation* flora, and herpetofauna are essen 

tially the same on the opposite sides of the Infernlllo 

ohannel (Appendices A and B)« In oontrast the mammals, 

and to a lesser extent the birds, indioate faunlstlo dif 

ferences (van Rossem, 1932, 19^5t Burt, 1932; Appendix C). 

These differenoes inolude evolutionary divergence, appar 

ently at the subspeoies level (Lowe, 1955)* and the 

absenoe of certain mainland forms from Tlburon (see p. 159)* 

Several Serl camps and Mexican fishing encampments 

are looated along the shore of the Infernlllo* There is 

some oattle grazing In the region between Rancho Noohe 

Buena in Seri pass (along the road to Hermosillo) and the 

coast* Otherwise most of the area is uninhabited and 

essentially natural• 

Shore Zone.—Littoral scrub is well developed along 

the Infernlllo in regions of gradually sloping topography. 

Elsewhere along the coast with low bluffs or cliffs shore

Figure 71. Aerial view of Infernillo channel; looking 

north. Mainland on right, hook-shaped 

peninsula in center is Punta Chueoa* Isla 

Tiburon on left* estero at Palo Pierro shows 

as a dark area in extreme left*

311

plants are largely absent* Maximum development of lit 

312 

toral scrub ooours with development of mangroves in shallow 

seawater esteros. 

The Infemillo marks the northern limit for man 

grove vegetation on the west coast of North Amerioa. Veil 

developed mangrove esteros are found at Punta Sargento, 

Punta Mala, and Santa Rosa. Shallow tidal inlets in these 

esteros are ologged with a closed-oanopy growth of man 

grove shrubs with little or no open water other than the 

tidal ohannels. The vertebrate fauna is restricted to 

fish and marine birds. Oysters are attaohed to the roots 

of Rhizophora mangle at Santa Rosa but have not been found 

on mangrove roots further north. 

Lower Ba.lada.—The lower edge of the bajada supports 

a coastal band of low scrub consisting largely of Frankenla 

palmerl which extends inland approximately 1 to 1*5 kms. 

Coastally it borders littoral scrub or, in instances where 

the bajada ends in bluffs or cliffs, it fronts direotly 

upon the shore. Inland it intergrades with the taller and 

more complex desertscrub of the middle bajada. Arroyos 

crossing the Frankenia belt oarry with them charaoterlstio 

middle bajada speoies which stand out in gallery-like files. 

The Frankenla zone bears a strong resemblance to that of the 

opposite shore on Isla Tiburon, and the only differences 

noted are the occurrences of a few rare speoies which are

not known from Tlburon, £•&•, Tlllaea ereota and Ommtla 

marlnae. 

313 

Middle and Upper Balada. —-The large perennials often 

appear to be relatively evenly spaced across the middle and 

upper bajadas (Fig. 72)• When viewed from an airplane in 

the late afternoon or early morning* when the shadows are 

prominent, it becomes evident that the larger perennials 

are in fact aligned along drainageways of reticulate pat 

tern! and are far less numerous and generally absent or 

rare from the islets between streamways. Most of the bajada 

surfaoe is relatively smooth and unbroken, the streamways 

are small and only shallowly cut into the surfaoe. These 

washes are not straight but spiral downhill perpendicular 

to the shoreline, frequently anastomosing and branching 

to form an overall reticulate pattern. Apparently they 

frequently shift course. 

There is a gradual change in species composition 

across the bajada with a general trend of rloher vegeta 

tion toward the upper bajada. One of the most distinctive 

features of the middle and upper bajada of the mainland 

side is the extensive development of Paohycereus prlnglel 

and other cacti which are relatively uncommon or absent 

from comparable sites along the Tiburon side of the 

Infernillo.

Figure 72. Aerial view of middle bajada on mainland side of 

Infernillo, at several kilometers north of Punta 

Chueoa. Dark areas in background are partially 

buried lava hills. The pattern of dots oonsist 

of small desert trees and shrubs*

314

Mountains.—Sierra Seri is one of the major mount 

ain masses along the coast of Sonora* Its summitt Ploo de 

Johnson* is at approximately 1,000 m* it is neither as 

high nor as massive as Sierra Kunkaak and the Guaymas 

Monadnook* Elevatlonal gradients in the vegetation were 

evident from aerial inspection* Desertsorub extends to 

the peak and subtropical scrub is evidently not developed 

here* In many ways the shallow-soiled rooky slopes at 

higher elevations resemble desertsorub communities on 

rhyolite peaks in the vicinity of Bahfa San Carlos* Some 

of the oonspicuous major perennials whioh occur to peak 

elevation on Pico de Johnson are: 

Acacia wlllardlana 

Agave 8i>»« large Euagave 

Fious palmerl 

Lemalreooereus thurberi 

Pachyoereus pringle1 

Exploration of the Sierra Seri range should be highly 

rewarding* 

315 

Aguajes or tinajas such as are found in Sierra Kun* 

kaak with Phragmltes communis colonies are not known from 

Sierra Seri* 

Vegetational gradients at Santa Bosa and between 

Sargento and Cerro Tepopa are discussed below* The Santa 

Hosa region may be taken as representative of the major 

portion of the Infemillo bajada and the Sargento region 

as indicative of the xerophytic vegetation lying largely 

to the north of the Infernillo region*

Santa Rosa 

The south end of the Infemlllo ohannel Is marked 

by Punta Santa Rosa. A similar low peninsula extends into 

the Infemillo on the Tiburon side of the channel and it 

confusingly is also known as Santa Rosa. 

316 

There are no signs of cattle grazing in the vicinity 

and the area is essentially uninhabited. A single north- 

south road of secondary quality traverses the area and 

another poor dirt road leads to the estero where tourists 

sometimes camp. Vegetational gradients were examined in a 

line extending eastward from the shore to the first hills 

at the upper end of the bajada. The distance from the 

shore to these first hills is roughly 5 kms. 

Strand.—South of the entrance to the estero a 

narrow sand spit approximately 50 to 100 m. wide and 2 to ^ 

m. high separates the mangrove estero from the sea. Dune- 

adapted and halophytic shore species produoe about 25# 

coverage on the low and semi-stabilized dunes. A list of 

these is given in Table 55> together with maximum heights, 

and abundant or rare species are indicated. Many of the 

shrubs exceed 1 m. in height but the majority of coverage 

is produced by plants less than 1 m. high. There are rela 

tively few species at any given site and species composi 

tion shifts relatively rapidly from one looale to another.

TABLE 55 

LIST OF SPECIES ALONG CA. 1/2 KM. OP STRAND, SANTA ROSA 

(MAINLAND), SOUTH STRAND PENINSULA BETWEEN ESTERO AND SEA. 

LOW AND PARTIALLY STABILIZED BEACH DUNES, CA. 2-4 M. ELEV. 

COVERAGE CA. 25%* 16 FEBRUARY 19^3" 

Species 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Jatropha clnerea 7-7 6.7 

Prosopls torreyana, rare 6.1 - 

Avloennla germlnans 6.0 4.6 

Lyolum sp.f abundant 6.0 4.9 

Allenrolfea oooldentalls, abundant 5.8 4.3 

Opuntla fulglda 5.4 

Maytenua phyllantholdes 5.0 4.2 

Croton oallfomlous, abundant U-.l 1.9 

Suaeda torreyana 3.7 - 

Dalea emoryl, abundant 2.3 1.8 

Opuntla blgelovll, rare 2.3 2.0 

Sporobolus vlrglnlous, abundant 2.2 1.7 

Palafoxla linearis 1.8 1.5 

Frankenla palmerl 1.7 1.6 

Atrlplex barclayana, abundant 1.3 1.1 

BatIs marltlma 1.2 - 

Sesuvlum verrucosum, abundant 1.2 1.0 

Abronla marltlma 0.9 0.7 

Euphorbia leuoophylla, abundant 0.6 0.4 

Mammlllarla sp. 0.6 - 

317

There are several common and repetitive patterns of over 

lapping speoies ranges of which the most evident include t 

1. Sporobolus virginious and Dalea emorvl 

2. croton oaTlformOA. Lvclum SP«. and Atrlplex 

barolayana 

• Croton oallfornioa and Avloennla peeralnans 

* Sesnviun verrucoaum and Allenrolfea ocoldentalls 

5* Euphorbia leuoophylla 

318 

These are the most abundant speoies on the strand. Euphorbia 

leucophylla. restricted to coastal dunes throughout its 

range in Sonora» is especially well developed here. The 

oocurrenoe of Avloennla germlnans on the dunes away from 

the estero is unique along the coast of Sonora. It is 

dwarfed here, does not oocur on the seaward side of the 

dunes, and its numbers quickly diminish away from the edge 

of the estero. In general, the communities on the windward 

side and on the more exposed knolls are reduoed in stature, 

and with a greater percentage of succulent plants than 

those on the more protected lee sides facing the estero. 

Estero.--»The physiognomy and the constituent speoies 

at the Santa Rosa estero are essentially similar to other 

mangrove areas along the ooast of Sonora. The species 

present are listed in Table $6 and maximum heights are 

indicated. The three west ooast mangroves are commons 

Avloennla germlnans. Laguncularla raoemoaa. and Rhlzophora 

mangle. Their ranges broadly overlap in a continuum pat 

tern. Rhlzophora shows greater development in deeper water

TABLE 56 

PLOT 5k. ESTEBO AT SANTA BOSA (MAINLAND). SHALLOW TIDAL 

SEA WATER AND WET SALINE SOIL. COVERAGE CA. 98jC. 


Speoies 

Maximum height 

(ft) 

ATioennla germinans 16.3 

Rhizophora Bangle 14.8 

Lagunoularia raoemosa 13^ 

Maytenus phyllanthoides 9.8 

Allenrolfea oooidentalis 5.8 

Salioomia paoifioa 2.*t 

Batis maritima 2.2 

Atriplei barolayana 1.9 

Monanthoohloe littoralIs 1.3 

Sesuvium verruooaum 

Cressa truilliensIs 

i 1.0 

0.6 

Total speoies in quadrat

than the other two speoies, Avlocnnla is oentered in the 

shallowest water and Lagunoularla generally occupies an 

intermediate position (Figs* 73 and 7*0 • Oysters are 

attaohed to the roots of Rhlzophora and orab burrows are 

320 

numerous among the mangrove roots* Halophytlo shore speoies 

fringe the mangroves and intermingle with the uppermost Avl 

oennia to form nearly 100# oover on the tldally inundated 

and permanently wet saline mud. On the higher saline and 

desert-dry soils, between the estero and the Frankenla zone, 

there is muoh barren ground. 

Lower Ba.1ada.~-The lower bajada at Santa Rosa is 

olearly marked by a well developed Frankenla zone (Fig* 75)* 

At the seaward edge of the lower bajada Frankenla palmerl 

occurs in nearly pure stand* Further inland, at approxi 

mately midway aoross the region arbitrarily designated as 

the lower bajada it reaches maximum density and other 

speoies are soon encountered, e*g*, Fouqulerla aplendens. 

Jatropha cuneata« and Manualliarla of* swingle1* Frankenla* 

Fouqulerla* and Jatropha form a oonsplouous band at the 

inland edge of the lower bajada* 

Plot 55 (Table 57, Fig* 75) was located about mid 

way aoross the short lower bajada in the vicinity of maxi 

mum concentration of Frankenla* Frankenla rarely exoeeds 

30 cms* in height here and accounts for most of the plant 

ooverage. Fouqulerla splendens and Opuntla fulglda are

Figure 73. Aerial view of mangroves In estero at Santa 

Rosa (mainland). Rhlzophora mangle with 

darker foliage and stilt roots (center) 

among Avlcennla germlnans with lighter- 

colored foliage.

Figure 7k* Mangroves at Santa Boaa (mainland)* Bhlzo- 

phora mangle (1), Avloennla germlnans (2), 

and Batls marltlaa and Salloornia paeifloa 

In foreground•

322

TABLE 57 

PLOT 55• SANTA ROSA (MAINLAND), CA. 150 M. INLAND (EAST) 

FROM ESTERO, CA. 2 M. ELEV. L0WES~BAJADA, SANDY PLAIN. 

COVERAGE CA, 30 Jg. 16 FEBRUARY I965 

Maximum Mean 



Paohyoereus pringlei - 17*1 

Fouquieria splendens 5 7*6 

Opuntia fulgida 1 5*3 

Bursera miorophylla - 5*1 

Lyoium 8p. 1 5*0 

Jatropha ouneata $0 2.7 

Errazurizia megaoarpa - 2.1 

Frankenia palmeri 2410 1.1 

Cressa truzilensis 3^ 0.5 

Mammillaria cf. swingle! 1 0.3 

Total 2502 





Cenchrus palmeri 



Mollugo oervlana 

Nama hlapldum 


Tillaea ereota 

Total Bpecies in quadrats 17 


6.9 

3.5 

i+.O 

3.9 

l.i* 

0.9 

0.5 

323

Figure 75* Lover bajada at Santa Rosa (mainland); looking 

east* Part of Sierra Serl range in background. 

Frankenla palmerl and few dwarfed Jatropha 

ouneata (foreground); Pouquieria splendens and 

Paohycereus prlnglei (background)

324

oonspiouous but not oommon while the other speoies are 

not readily notioed. The speoies here have relatively 

small leaves or are aphyllousf and larger-leaved ones are 

not present. Cressa truxlllensls reaohes its inland limit 

here, being more oommon along the margin of the nearby 

estero. The remaining speoies are mostly oharaoteristio 

of the middle bajada and poorly represented* Jatropha 

ouneata is fairly oommon but remains dwarfed with a maxi 

mum height of only 0.? m« or a mean maximum height of 0.3 

325 

m. Twenty speoies are present of whloh half are ephemerala* 

The ephemeral populations are meager and oomposed of strag 

glers from the nearby middle portions of the bajada. Only 

four of the 10 speoies of perennials are oommon enough to 

be Important members of the oommunltys Frankenla palmer!. 

Jatropha ouneata. Fouqulerla splendens. and Cressa truxll 

lensls. 

Middle Bajada.—The lower edge of the middle region 

of the bajada is oharaoterized by the narrow overlapping of 

the seaward limits of mixed xerophytlo desert shrubs and 

the Inland limits of Frankenla palmer! (Plot $69 Table $8, 

Fig. 76). The dominant growth is of mixed desert shrubs 

In whloh Bursera mlorophylla. Cordla parvlfolia, and Larrea 

dlvarloata play an important role. Maximum orown heights 

range from 1.5 to k m. in height. Nineteen speoies of 

perennials and 9 of ephemerals are present. The ephemeral

TABLE 58 

PLOT 56. SANTA BOSA (MAINLAND), CA. 1/2 KM. INLAND (EAST) 

FROM ESTERO SHORE, £A. 8 M. ELEV. LOVER EDGE OF MIDDLE 

BAJADA, SANDY PLAIN. COVERAGE CA. 50%. 


Maximum Mean 





Ceroidlum mlorophyllum 1 7.2 - 

Larrea dlvarloata 50 5.8 - 

Cordla parrifolia 50 5.4 5.4 

Simmondsla ohlnensls - 5-3 5.2 

Opuntla fulglda 22 5.2 wm 

Lyolum sp. 2 4.7 4.4 

Maytenus phyllantholdes - 3.7 3.4 

Hlbisous denudatus 16 2.9 2.2 

Kramerla grayl 2 2.9 2.2 

Wilooila striata 2 2.7 - 

Errazurizla megaoarpa 4 2.6 2.0 

Jatropha cuneata 33 2.0 - 

Lemaireooerous thurberi - 1.9 - 

Franseria dumosa 17 1.8 1.6 

Frankenla palmer! 185 1.4 1.1 

Ferrooaotus sp - 1.0 mm 

Mammillarla of. swingle! 5 0.4 - 

Total 436 




Dalea mollis 

Ditaxis neomezloana 

326



Oligomeris llnlfolia 





Figure 76* Lower edge of middle bajada, Santa Boaa (main 

land) ; looking east* Fouaulerla splendens. 

Frankenla palmerl. and Larrea dlvarloata.

328

populations show marked inoreaae from the lower bajada 

(Table 57) but are yet sparse in comparison with areas 

further inland* Pranserla dumosa is present in moderate 

numbers. Frankenia nalmerl is common but substantially 

reduoed in numbers as compared with the lower bajada and 

329 

is essentially at its inland limit here. Maytenus phyllan- 

tholdea is rare and also does not range appreciably further 

inland. 

Plot 57 (Table 59) was placed in the upper portion 

of the middle bajada at approximately 1.5 kms east and 

inland from Plot 56. Although xerophytic, the vegetation 

Is somewhat richer than that nearer the shore. The most 

prominent major perennials include Cercldlum mlorophyllum. 

Pranserla dumosa. Larrea dlvarloata. and Pachyoereus 

prlnglel. Pranserla dumosa reaches its maximum development 

while Larrea dlvarloata occurs in somewhat diminished num 

bers as compared with its stand in Plot 56. A total of 37 

speoies was found in the stand and 30 in the quadrat. The 

13 species of ephemerals form much larger populations than 

they do in lower and seaward portions of the bajada plain. 

Upper Bajada,—Toward the base of the first foot 

hills of Sierra Serl the bajada vegetation becomes notioe- 

ably rloher (Plot 581 Table 60, Figs. 77» 78t an ^ 79)• The 

general physiognomy of the landscape resembles the middle 

portions of the bajada but many of the plants reach greater

TABLE 59 

330 

PLOT 57* SANTA ROSA (MAINLAND)9 CA* 2 KMS* INLAND (EAST) 

PROM ESTERO SHORE, CA* 15 M. ELEV. MIDDLE BAJADA, GRAVELLY- 

SAND PLAIN* COVERAGE CA* 16 FEBRUARY 1965 

Species 

Number 

(0*1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Paohyoereus prlnglei 7 27.0 22*5 

Lemaireooereus thurberi 2 13.0 12*1 

Bursera miorophylla 10 10*7 10*5 

Ceroldium miorophyllum 12 10*2 7.3 

Colubrlna glabra 16 8*9 6.k 

Jatropha clnerea 9 8*1 7.3 

Bursera hlndsiana - 8*0 - 

Larrea divarioata 33 7.2 6*2 

Horsfordia alata - 6*1 5.8 

Wilooxia striata - 5.8 - 


Simmondsia ohlneusls 3 5.2 5.1 

Perrooaotus sp* - 5.1 3.9 

Opuntla fulglda 9 5.0 3.7 

Trills oallfomioa - *t*6 4*1 

Cardiospermum oorindum - J**5 - 

Jatropha ouneata 15 3*8 3.3 

Ditaxis lanoeolata - 3.6 - 

Hibiscus denudatus 3 3.3 - 

Condalia globosa - 3.2 - 

Errazurlzia megaoarpa 12 3.2 2*6 

Krameria grayl 11 2.7 2.3 

Opuntla leptooaulis 1 2*6 2*2 

Franserla dumosa 79 2*4 1.9 

Mammlllaria sp* 3 2.1* -


Phoradendron oallfomloum 2 

Total 217 







Ditazis neoaezioana 







Tidestronia lanuginosa 



TABLE 60 

332 

PLOT 58* SANTA BOSA (MAINLAND), CA. 3 KMS. INLAND (EAST) 

FROM ESTERO SHORE, CA. 30 M. ELEV. UPPER BAJADA, GRAVELLY- 

SAND PLAIN, COVERAGE CA. 50#. 16 FEBRUARY 1965 

Haxlnum Mean 



Paohyoereus prlnglel - 45 - 

Lemaireooereus thurberi 2 15*7 13.8 



Corcidium mlcrophyllum 4 11.1 10.4 


Bursera hindsiana - 7.8 - 

Jatropha euneata Ik 7.7 5.6 



Euphorbia zantl - 6.9 - 

Krameria grayi 8 6.1 - 

Cordla parvifolia - 5.4 - 

Cardiospermua oorlndum - 5.3 - 

Trlxis oalifornloa - 5.1 - 

Ditaxls lanoeolata 5 5.1 4.3 

Maohaeroeereus gummosus - 5.0 - 

Slanondsla ohlnensls 34 4.8 4.1 

Lophooereus sohottll - 4.7 - 

Janusia oalifornloa - 4.7 - 

Koeberllnla spinosa - 3.8 - 

Larrea dlvarloata 2 3.8 - 

Errazurlzia megaoarpa 3 3.4 2.7 


Hibiscus denudatus 10 3.1 3.0

TABLE 60 —Continued 

Lippla palmeri 1 2.8 

Hoffmanseggia intricate 1 2.*f 

Franserla dumosa 11 2.1 1.9 

Aoalypha callfornlca 1 1.8 

Total 1^9 



Antirrhinum cyathiforum 

Arlstida adsoenslonls 



Cusouta sp. 

Datura dlseolor 





Feotls papposa 


Phaseolus fillform!s 

Total speoies in quadratt 

Total species in standi 

33 

^3 

333

Figure 77. Upper bajada, Santa Eosa (mainland); look 

ing east* Bursera mlorophylla. Slamondsla 

ohlnensls (oenter, extreme foreground)» and 

Paohyoereus prIngle1» Low ground herbs con 

sist primarily of Euphorbia polyoaroa.

334

Figure ?8. Upper bajada, Santa Rosa (mainland). Eursera 

mlorophvlla and Jatropha ouneata (left)* Pole 

is 5 feet.

335

Figure 79 • Upper bajada at Santa Rosa (mainland). A very- 

large Paohyoereus prlimclel. ca. k5 feet high. 

Koeberllnla aplnosa at base and right of Paohy 

oereus. Pole is extended 2$ feet.

336

337 

stature and at a given date Individuals of the same species 

may carry more foliage than their lower elevation counter 

parts. A gargantuan individual Paohycereus prlnglel 

measured 18 m. in height (Fig. 79). although maximum height 

for most of the population seldom exoeeds 8 to 10 m. The 

total number of speoies is greater here than in any other 

community studied along the mainland side of the Infemlllo. 

Forty-three speoies were present in the stand and 33 in the 

0.1 ha. quadrat. The ratio of perennial to ephemeral speoies 

is nearly 2. Fourteen ephemerals are present and thus it Is 

seen that both perennials and ephemerals locally reach 

greater expression here than in more xeric habitats. 

Hills.—Low oonical hill3 of voloanic origin lie 

scattered along the upper edge of the bajada. Their bases 

are burled by the outwash from Sierra Seri, and the darker 

voloanic rook soils of these hills contrast conspicuously 

with the lighter-colored bajada surfaoe. A representative 

stand was ohosen on the southwest-facing side of suoh a 

hill (Plot 59f Table 6l) at about 1/2 km. east (inland) 

from Plot 58 (Table 60). The hill slopes steeply to 

approximately 20 m. above the surrounding bajada. The 

southwest exposure and shallow soil contribute to the 

harshness of the habitat and the small hill does not 

receive additional soil moisture from runoff. The stature 

and ooverage of the vegetation is substantially reduced

TABLE 6l 

PLOT 59. SANTA ROSA, MAINLAND, CA. 3.5 KMS. INLAND (EAST) 

FROM ESTERO SHORE, CA. 40-55 M. ELEV. HILL, 20 M. HIGH, 

REDDISH VOLCANIC ROCK, SHALLOW SOIL, SOUTHWEST EXPOSURE, 

220°, SLOPE 27*. COVERAGE CA. 15 FEBRUARY 1965 

Species 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Desmanthus frutieosus 1 9.1 7.5 

Ceroidium microphyllum 9 9.0 7.6 

Paohycereus pringlei - 7.1 - 



Colubrina glabra 5 5.9 - 

Meloohia tomentosa 31 ^.7 4.0 

Lyeium sp. 2 4.6 - 

Carlowrightla sp. 12 3.8 - 

Simmondsia chinensis 4 3.7 - 

Janusia oalifornioa 8 3.6 - 

Ditaxis lanoeolata 77 3.0 2.9 


Trixis oalifornioa - 2.8 - 


Krameria grayi 1 2.4 - 

Cassia oovesll 82 2.1 1.7 


Fagonia oalifornioa 128 1.2 0.9 

Mammillaria sp. 2. 0.3 - 

Total 586 


Arlstlda adaoenslonla 


Boerhaavie of* ereota 

338

Bouteloua aristldoldes 

Cassia covesil 


Dalea mollis 

Dalea parryl 






TABLE 6l--Continued 


Total speoles in standi 32

from that of the adjaoent bajada. Yet the oommunlty 

approaches the middle bajada in number of speoies which 

include 32 in the stand and 30 in the quadrat* Xerophytio 

desert shrubs form the dominant elements, e.g., Ceroidlum 

mlorophyllum. Bursera mlorophylla. Jatropha ouneata. and 

Errazurlzla aegaoarpa« Cassia covesll and Fagonla call- 

fornioa are abundant and looally do not extend onto the 

adjacent bajada. Desmanthus f rut loo sue is relatively com 

Jko 

mon at the base of the slope on the volcanic soils but rare 

on the nearby bajada. Pachvoereus prlnglel occurs on the 

hill in substantially reduoed stature and numbers as com 

pared with Its stature and numbers on the bajada. 

Sargento 

Punta Sargento is a well known landmark delimiting 

the north end of the Infemillo ohannel. The vegetational 

gradients described below extend from near the base of the 

Sargento peninsula across the bajada to the first foot 

hills at the south side of Cerro Tepopa. A small fishing 

village, Campo Dollar, lies near the northwest base of the 

peninsula. A seoondary dirt road leads to Campo Dollar 

and semi-nomadic Seri Indians have long lived in the area. 

The vegetation, exoept that very near the fishing camps, 

appears to be essentially unaltered by man. Firewood, 

however, seems to be especially scaroe near the roads.

The bajada is roughly 2.5 kms. in width here and 

3^1 

elopes evenly and with few deteotable streamways. The soil 

oonsists mostly of decomposed gravel outwash from the 

granites of Cerro Tepopa. 

Estero.—The estero at Sargento extends nearly 5 

kms. along the shore south of Punta Sargento. The man 

groves produoe 100J< oover over all ezoept the tidal chan 

nels of the estero waters* Aside from the small disjunct 

oolony of Avloennia germlnans at Bahfa Tepooa (Johnston, 

1924), the Sargento estero marks the northern limit for 

mangroves in western Mexico. The mangroves here are vigor 

ous and show no signs of reduced development. All three 

Sonoran species of mangrove are present. Common estero 

species at Sargento follow the same distribution pattern 

which obtains in other esteros further south and inoludes 

Allenrolfea ocoldentalls 

A triplex barclayana 

Avloennfa germlnans 

Batis marltlma 

Crcasa""truxlllcnsl s 

Laminoularla raoemosa 

Mavtenus phylTantholdes 

Wonanthochloe 11ttoralis 

Rhlzophora mangle 

Salloornla paclflca 

Sesuvlum verrucosum 

Sporobolus virgin!ous 


Lower BaJada.—The lower bajada fronting upon the 

littoral sorub of the estero supports a sparse oover of 

Prankenla palmerl in nearly pure stand. Further inland,

at about midway across the lower bajada, Frankenla reaohes 

Its maximum density and several additional species are 

present (Plot 6of Table 62)• Jatropha ouneata is present 

in limited numbers and remains dwarfed, attaining a maxi 

3^2 

mum height of only 4>5 to 65 cms* Two speoies of ephemerals 

were found and these were uncommon: Aohyronyohla cooperl 

and Peritvle emoryl* A total of only 7 speoies were in the 

stand* 

Middle Ba.lada.—Large and evenly spaced saroo- 

caulesoent perennials and xerophytio desert shrubs char 

acterize the middle bajada (Plot 6l, Table 63)* Pachyoereus 

prIngle1 of ponderous sizes are relatively dense9 l*e«» 7 

per 0,1 ha. The total number of individuals of the major 

perennial speoies in Plot 6l is relatively low; however, 

the individual plants tend to be especially large and 

broadly spreading* Bursera microphylla and Ceroldlum 

mi ft-rophyi i nwi form small trees often with their limbs arch 

ing over to the ground and thence extending to give a dia 

meter of up to about 10 m. Along the Infemillo the large 

Individuals of the major perennials commonly ooour on non- 

eroded substrates. This may allow them to reach greater 

sizes and ages than they can attain on eroding or shifting 

surfaces where larger specimens may beoome undermined and 

ultimately topple over. The most oonsplouous elements of 

the landscape Include Cercldlum mlcrophyllum. Jatropha

TABLE 62 

3^3 

PLOT 60. SARGENTO, CA. 1/2 KM. INLAND (NORTH) PROM SHORE AT 

ESTERO, CA. 2 M. ELEvT LOWER BAJADA, FINE-TEXTURED SILT 

LIKE SALINE SOIL. COVERAGE CA. 30%. 19 FEBRUARY 1965 

Speoles 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Opuntia fulgida *.3 3.2 


Frankenia palmerl 1158 1.3 1.0 

Paohyoereus pringlei Oft 1.1 - 

Mammlllaria sp. 1 0.3 mm 

Total 1197 


Aohyronyohia oooperl 



Total speoles in stand: 7

TABLE 63 

344 

PLOT 61. SARGENTO, CA. 1.5 KMS. INLAND (NORTH) FROM SHORE 

AT ESTERO, CA. 15 M. ELEV. MIDDLE BAJADA, DECOMPOSED GRANI 

TIC GRAVEL 3!fo SAND SOIL. COVEBAGE CA. 20*. 18 FEBRUARY 1965 

Maximum Mean 



Paohyoereus pringlei 

Fouquleria splendens 

Olneya tesota 

Ceroldium mlorophyllum 

Maohaerooereus gummosus 

Larrea dlvarloata 

Jatropha olnerea 

Lemaireooereus thurberi 

Opuntia fulgida 

Bursera miorophylla 

Lyolum sp. 

Enoella farinosa 

Lophooereus sohottii 


Opuntia blgelovii 

Errazurizla megaoarpa 

Dalea emoryi 

Krameria grayl 

Mammillaria sp. 

Total 





Total speoies in quadrats 

Total speoies in stands 

15 35 30.8 

- 16.1 - 

- 14.1 - 

18 13.1 11.5 

- 8*5 7*7 

25 8.1 6.8 

53 7.7 7.0 

- 6.2 - 

29 6.2 4.2 

2 6.1 - 

13 5.8 5-6 

23 5.2 3.8 

- 4.6 - 

22 3.2 3.0 

203 

14 

22 

- 3.1 m 

2 3.0 2.4 

1 2.8 2.7 

- 1.5 - 

- 0.3 -

clnerea. Larrea dlvarloata* and Paohyoereus prlnglel* 

Twenty-two species are present in the stand of which lit 

ooour in the quadrat* There are only three herbaceous 

species and two of these are faoultative perennialsi 

Euphorbia polycarua and Pitaxis neomexloana. Additional 

ephemerals may be present during more favorable years* 

3^5 

Upper Bajada.—The upper bajada appears to be rela 

tively arid, seemingly beoause of its south exposure and 

for being at the base of the south side of Cerro Tepopa. 

Vegetation on low, flat-topped ridges (Plot 62, Table 6*0 

is more xerophytic than it is on adjacent and slightly lower 

plains of the upper bajada (Plot 63» Table 65)* Reasons for 

the xeric conditions of the ridge-plains seem to be laok of 

runoff water from adjacent areas and a roolcier and shallower 

substratum* In Plot 62 there are no large individuals of 

Paohyoereus prlnglel and the dominant elements inolude 

Fouqulerla splendens, Jatropha ouneata* and Larrea dlvari- 

cata. Only 15 speoies are present in the stand and 14 in 

the 0*1 ha* quadrat* 

In Plot 63 mature individuals of Paohyoereus are 

common* Other dominants Inolude Jatropha ouneata and Larrea 

dlvarlcata* Twenty species are present in the stand and 

only 15 in the 0*1 ha* quadrat. 

The upper bajada may be interpreted as being rela 

tively arid because of the paucity of species. However,

TABLE 64 

PLOT 62. SARGENTO, CA. 2.5 KH3. INLAND (NORTH) FROM SHORE 

AT ESTERO, CA. 40 H. ELEV. LOW AND VIDE FLAT-TOPPED RIDGE 

IN UPPER BAJADA. ROCKY SOIL. COVERAGE CA. 15%. 


Maximum Mean 


Speoies (0,1 ha) (ft) (ft) 

Fouquieria splendens 23 13^1 11.1 

Olneya tesota 1 10.1 oft 

Paohyoereus pringlei 1 6,2 - 


Opuntia fulgida 4 5.5 5.1 

Larrea divarioata 8? 5.0 3.7 

Bursera miorophylla - 4.6 

Opuntia bigelovii 2 2,6 - 


Errazurizia megaoarpa 3 1.4 - 

Mammillaria sp. 2 0-3 - 

Total 220 




Oligomeris linifolia 




346

TABLE 65 

PLOT 63. SARGENTO, CA. 2.5 KMS. INLAND (NOBTH) FROM SHORE 

AT E3TERO, CA. 35 M. ELEV. UPPER BAJADA, DECOMPOSED GRANI 

TIC GRAVEL AND SAND SOIL. COVERAGE CA. 15#. 


Speoles 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Paohycereus pringlel 6 24.8 23.4 

Fouquierla splendens 17.4 - 

Olneya tesota mm 11.0 mm 


Ceroldlum miorophyllum 5 10.4 10.1 

Bursera hlndslana - 10.1 - 



Larrea divarloata 55 6.1* 5.6 

Opuntia fulglda 15 5.6 4.6 

Hyptis emcryl - 4.8 - 

Hibiscus denudatus 9 3-8 2.6 

Opuntia blgelovll 1 3.6 3.0 

Errazurizla megaoarpa 21 3.° 2.6 

Mammlllarla sp. - 0.4 - 

Total 148 



Ditaxis neomexlcana 





Total speoles in stand: 20 

347

additional ephemeral speoles may he expected. Yet at 

nearly the same date nearby regions, e.g., Santa Rosa, 

supported a higher number of ephemeral speoles and larger 

populations thereof. The occurrence of suoh highly xero- 

phytic speoles as Larrea dlvarloata. Jatropha ouneata. 

Fouaulerla splandens. and Qpuntla blgelovll across most of 

the bajada and onto the upper bajada also indicates arid 

conditions* 

Hills.—The lowermost outlying foothills at the 

south side of Cerro Tepopa are nearly 3 tons, inland from 

the estero at Sargento. These granitio hills are thinly 

vegetated with relatively xerophytio speoles (Plot 64, 

Table 66}• Plot 64 was plaoed on the south-faolng slope 

of a hill which is approximately 25 m. high. Jatropha 

ouneata is the most common perennial and Larrea dlvarlcata 

348 

is of secondary importance. It is interesting to note that 

Larrea occurs in well developed stands on the granitic 

slope. Ephemerals were especially rare. A total of 19 

species were found on the hlllslope and 15 occurred in the 

quadrat. The south slope and lack of runoff from adjacent 

area seem to be factors contributing to the observed 

aridity. 

Summary.--The vegetation and flora of the mainland 

side of the Infemlllo resembles the adjacent east side of 

Isla Tlburon. Vegetational differences on the opposite

TABLE 66 

349 

PLOT 64. SARGENTO, CA. 3 KMS. INLAND (NOBTH) PROM SHORE AT 

ESTERO» CA. ?0 M.ELEV7 SMALL GBANITE HILL NEAR SOUTH SIDE 

OF CERRO TEPOFA. SOUTH EXPOSURE, SLOPE 22%. COVERAGE CA* 15%. 


Species 

Number 

(0.1 ha) 

Maximum 

height 

(ft) 

Mean 

height 

(ft) 

Cercidium miorophyllum 2 10.1 9.9 

Fouquieria splendens 1 9.2 - 


Lycium sp. - 6.6 - 



Machaerooereus gummosus - 6.3 - 

Larrea divarioata 2k 5.5 5.3 

Opuntia fulgida 4 5.1 - 

Opuntia blgelovll 10 2.9 - 

Hoffmanseggia intricata - 2.7 mm 


Pachyoereus pringlei 5 2.1 - 

Errazurizla megaoarpa 3^ 2.0 1.9 

Fagonia oalifomioa 4 1.2 - 

Total 20? 








sides result largely from differences in slope exposure 

of the long bajadas and the adjacent mountains* The west- 

350 

facing slopes of the east side (mainland) of the Infernillo 

are, therefore, more xerophytio. The north end of the 

Infernillo region, e*£*, in the vicinity of Cerro Tepopa 

and Punta Sargento, is markedly more xerophytio than the 

remaining southern portions of the region* 

Desertsorub in the Sierra Seri, on the mainland 

east of Isla Tiburon, extends to peak elevation on Pioo 

de Johnson and shows gradual zonation aoross the relatively 

unbroken bajadas eastward* The desertsorub oommunities 

include dune communities, coast shrub (Frankenla palmeri). 

mixed desert shrubs with Larrea divarlcata and Franseria 

dumosa, oardonal, and mixed small desert trees and shrubs* 

Mangroves occur at several esteros and here mark their 

northern limits along the Sonoran coast*

I SLA. PATOS 

This tiny guano-covered island lies in open water 

351 

several kilometers north of Xsla Tiburon. A single oonioal 

peak rises to approximately 70 m. from a broad and rela 

tively level plain about 4 to 5 i> high. The total surface 

area does not seem to be more than 0.3 to 0*5 sq. km. 

Gentry (19^9* P* 100) states, "In 19^5 all the 

sporophytes were stripped off Patos Island by a Mexican 

guano mining company and the guano producing Peruvian 

cormorant was introduced." The date, however, may be 19^6 

as evidenoed by a series of photographs of plants of the 

island. These photographs, primarily of oaoti, are in the 

herbarium of the Allan Hancock Foundation at the University 

of Southern California and are labeled ". • • before clear 

ing of the island by Guanos y Fertilazantes de Mexico. 

Photo by B. F. Osorio Tafal, Feb. 1946." Figures 80, 81, 

and 82 are copies made from these photographs. 

The only terrestrial vertebrate is a lizard, Uta 

stansburlana. which is oommon. Individuals are unusually 

wary and quick to dart under a rock. Such behavior seems 

to be an adaptation to the pressure of predatlon from the 

large bird population and the relative lack of vegetation 

cover• 

The flora is one of the most depauperate of any of 

the Sonoran islands and consisted of only nine speoles

Figure 80. Iala Patos, looking north from south shore. 

Photograph by B. P. Osorio Tafal, 1946. 

Atriolex barolayana and Paohycereus pringlei.

352

Figure 81. Isla Patos, near southeast shore. Photograph 

by B. P. Osorlo Tafal, 1946. Atrlpies bar- 

clayana. Camagiea glgantea (arrow) t Lopho- 

eereus schottll. Qpuntla fulglda. and Paohy- 

oereus prlnglel.

Figure 82. Isla Patos, near south shore. Photography by 

B. F. Osorlo Taf al» 19^6. Atrlplex barclayana, 

and Ifaohaerooereus gaunmosus.

354

prior to 19^6* 

Aaaranthua flmbrlatus 



Carneglea gjgantea 

Lophooereua aohottii 

Machaerocereua gummoaus 

Qpuntla fulKlda 

Paohyoereus prlnglai 

Moat of the vegetation now present on the i8land 

oonsists only of one Chenopodlaoeae, Atriplex barolayana. 

and two Caotaceae, Paohyoereus prlnglel and Qpuntla ful- 

gida (Fig* 83)• Aaaranthua flmbrlatus and Lophooereua 

aehottll (and presumably Bouteloua barbata) form only 

8mall populations whloh comprise but an inaignifioant 

portion of the vegetation* Carneglea gjgantea (Fig* 81), 

Enoella farlnoaa. and Maohaerooereus gummoaus (Fig* 82), 

are now eztinot on Iala Patos and apparently were not com 

mon before 19^6 • The total vegetation oover is aparae and 

355 

conal8ta largely of Atrlplex barolayana (below). The oaoti 

produce less than 1% oover except in small looallzed areas. 

The 19^6 photographs show that the vegetation was 

essentially similar to that at present and thoae species 

whioh did not reoover were rare. I do not lmow how 

thoroughly the vegetation was removed but it would have 

been relatively eaay to destroy practioally every peren 

nial plant except Atrlplex barolayana. and it aeema that 

thia was done. Thua the meager vegetation recovered

Figure 83. Isla Patos, August, 1964. Atrlplex barolayana 

(foreground, dried up), Qpuntia fulgida (dark- 

appearing shrubs, oenter), and Paohyoereus 

prlnglel (right). Note ruins of guano workers' 

shelter on left*

356

directly with no evidence of succession although several 

rare species were not able to become re-established* 

The growth-forms on the island are indicative of 

highly zerlc conditions, viz.. aphyllous stem succulents 

357 

(cacti), a sucoulent-leaved perennial (Atrlplex barolayana). 

and two ephemerals (Amaranthus fimbrlatus and Bouteloua 

barbata)> The single drought-deciduous desert shrub 

(Enoella farinosa) is no longer present. 

Species acoounts for the plants known from Isla 

Patos are given below. 

Amaranthus fimbrlatus.—Johnston (192^, p. 1018) 

oolleoted this ephemeral forb in the spring of 1921 and 

stated that it was • • common with Atrlplex on the low 

guano flat." I found it August 196^ as a very small and 

localized population of diminutive and delicate plants near 

the ruins of the rock shelter built by the guano workers. 

Atrlplex barolayana.—In the first few weeks of 

March 1963 much of the level area of the island was bright 

green due to great numbers of this species. Host of these 

were small plants which had germinated with rainfall of the 

same season and were not of flowering age. Both perennial 

individuals and young plants were most numerous along the 

shallow gullies or depressions in the guano flat where they 

formed nearly 100$ oover. On the higher portions of the 

flat and on the hill the density thinned appreciably, yet

it was sufficiently dense to turn the otherwise white 

guano slopes conspicuously green. By April 7 of the same 

year most of that season*s orop had perished, or dried up, 

and the foliage on the remaining plants was turning brown. 

Perennial cover of Atrlplex across the flat amounts to 

roughly 10% of the total ground surface. If all of the 

perennial individuals were removed in 1946 the effect on 

the population would have been only temporary because of 

the great quantity of seed present in the soil. 

Bouteloua barbata.—Johnston (1924, p. 983) col 

lected it in the spring of 1921 and stated that "several 

large colonies of this species were found with Atrlplex on 

the guano-covered flats • • • . M I have not found it on 

the island but negative data for an ephemeral is scarcely 

conclusive. 

358 

Carneglea glgantea.—Johnston (1924, p. 1108) dis 

covered saguaro in 1921: ". • . the single plant on Patos 

fsiand is over 12 m. high and has a single large branch." 

Another saguaro is evident in one of Osorio Tafal*s 1946 

photographs (Fig. 81). It was an unbranched plant about 

3 to 4 m. high and grew below the low rook ledge at the 

southeast shore of the island. The 1946 photographs show 

the prominent cacti of the island and if a saguaro of the 

dimensions given by Johnston were still present it is 

likely that it would have been photographed. The species 

no longer exists on the island.

Encella farlnosa var. phenlcodonta.--Mature speci 

mens were recorded by Johnston (19240. It does not show 

in any of the 1946 photographs and I suspect that it was 

never common* It no longer occurs on the island. 

Lophocereus schottll var. schottii•—Two specimens 

are evident in Osorio Tafal's photographs, one of which is 

shown in. Fig. 81. A single plant is now present in nearly 

the same place at the low rocky ledge near the southeast 

corner of the island. The Individuals shown in Tafal's 

photograph and the living plant are olearly of the same 

ecotype as on the adjacent mainland and Isla Tiburon. 

Machaerocereus gummosus.—A single mature plant or 

359 

colony occurred in 1946 at the south edge of the flat (Fig. 

82). It is no longer present on the island. 

0puntla fulglda.—Colonies of mature individuals 

heavily laden with pendulant chains of fruit occur at the 

rocky ledges near the southeast shore and also on the flats 

near the base of the hill. Before the clearing of the 

island in 1946 it occurred at least at the former site and 

was common (Fig. 81). Destroying mature speoimens would 

not have eradicated the population unless the numerous 

joints and fruit were also removed, as reproduction is 

primarily from fallen fruit which produce vegetative sprouts. 

Pachycereus prlnglel.—The 1946 photographs show a 

very thinly distributed stand across the flats (Fig. 80)

where it is today absent except for one medium-size plant 

(Fig. 83). Two colonies are also visible in the older 

photographs, one at about half way up the south side of 

the hillslope and another at the rocky ledges near the 

southeast shore. The hillside colony consisted of larger 

individuals and seems to have been slightly bigger than 

the one near the shore. Today Paohyoereus ocours in the 

same places but the individual plants are markedly smaller 

than those shown in the 1946 photographs. The population 

is recovering but the plants have not yet reached maximum 

size. 

Summary.--The terrestrial fauna and flora of Isla 

360 

Patos are the most depauperate of any of the Sonoran islands 

studied in this work. Aridity, guano, and relatively little 

habitat diversity appear to be principal factors limiting 

the terrestrial biota* The life-form spectrum is simple 

and also indicative of highly xerlc conditions* The domin 

ant elements are comprised of several Cactaceae and one 

Chenopodlaceae* The vegetation was cleared in 19^6 for 

the purposes of guano mining. Subsequently the vegetation 

has recovered directly with no signs of succession* How 

ever, several rare species never recovered and are now 

extinct on the island. Uta stansburlana is the only terres 

trial vertebrate. There are no endemics among the terres 

trial biota*

DISCUSSION 

The Vegetation Continuum and Mosalo 

The desertsorub and thomsorub vegetation of the 

Sonoran Gulf Coast clearly exhibit both continuous and 

discontinuous species distribution patterns, and both con- 

tlnua and mosaics accordingly occur* While the mosaics are 

numerous and are conspicuously sharp in their spatial bound 

aries, population distributions on the whole, throughout the 

Gulf Coast, most often exhibit contlnua over more or less 

gradual environmental gradients. 

Frequenoy distributions of six oommon species at 

Santa Rosa are dlagrammatloally shown in Figs 8*+ and 85* 

The oontlnuum-llke distributions are characteristic of 

population distributions throughout the Gulf Coast* Some 

of the xerophytlc species show two population peakst one 

on the lower or middle bajada and the second on the south- 

facing slope* They are fewer in number at the relatively 

more mesic upper bajada. 

In addition to the usually encountered continuum 

distribution (Whittaker, 1951# 1953» 1957; Brown and Curtis, 

1952) in desert and thornscrub, mosaic patterns ocour where 

361

Figure 84, Frequency distribution of three common species 

(Cercldium mlcrophyllunii Hibiscus denudatus, 

and Slmmondsla chlnensls) sampled at four quadrat 

sites across the environmental gradient at Santa 

Rosa, Infernlllo Region. Distance from lower 

middle bajada to south-facing slope is ca« 3*0 

kms. The numbers on the abscissa Indicate the 

table from which the data was taken.

40 

30 

tn 

o 

3 

T3 

> 20 

"O 

0> 

Xk 

E 

10 

58 

Middle 

bajada 

59 

Middle 

bajada 

J I 

60 61 

Upper South facing 

bajada slope 

oi 

o> 

ro

Figure 85* Frequency distribution of three common species 

(Errazurlzla megacarpa. Jatropha cuneata, and 

Larrea divarlcata) sampled at five quadrats 

aoross the environmental gradient at Santa 

Rosa, Infernlllo Region. Distance from lower 

bajada to south~facing slope is ca. kms. 

The numbers on the absoissa indicate the table 

from which the data was taken.

Lower 

bajada 

58 

Middle 

bajada 

59 

Middle 

bajada 

60 

Upper 

bajada 

iu 

I 

61 

South facing 

slope

the environmental gradients are so steep or sharp as to 

preolude environmental lntergradatlon, or a continuum, and 

364- 

form instead an environmental mosaic (see Lowe, 1959» 196*0. 

The sharp overhanging sea ledges at Bahfa San Carlos pro- 

' T" 

duce an environmental and vegetational mosaic between man 

groves and mixed desertscrub communities. Elsewhere in the 

same bay where the ledges are absent and the environmental 

gradients are relatively gradual a continuum distribution 

prevails. The steep and narrow oanyons on the east side of 

Isla San Pedro Nolasco (Fig* 22) form a near mosaic between 

the grassy north-slopes and the cactus and desertscrub 

climax on the south-faoing slopes. 

Species Distribution 

The preoedlng descriptions of a number of desert 

and thorasorub communities along the eastern side of the 

Gulf of California, as summarized in Table 67 (pp. 365-372)t 

show olose relationship between number of species per unit 

area or community stand and the habitat and climax vegeta 

tion. In general mesic habitats support greater numbers 

of species per oommunlty stand, or area, than do relatively 

less mesic, more xerlc environments. Thus thornsorub or 

thornscrub-1ike climax communities (£•&., Tables 3» 6, 8, 

and 15) definitely support significantly greater numbers 

of plant species than desertscrub climax (e.g., Tables 1,

TABLE 67 

SUMMARY OF HABITATS, COMMUNITY INDICATORS, AND NUMBERS OF SPECIES IN QUADRATS 

AND COMMUNITY STANDS. SEE FIGS. 83 AND 84 

Quadrats Number of Number of Characterization 

In Table Species in Speoies in of 

Number Quadrat Stand Habitat Vegetation 

Vicinity Bahfa San Carlos 

1 20 21 upper beach palm, salt grass, 


2 24 26 low ridge-crest Larrea divaricata. 

JatroDha cuneata 

3 48 61 swale between 

ridge-crest 

thornscrub 

4 44 50 upper bajada small desert trees, 


5 37 38 rhyollte headland, 

shallow 

soil 

6 51 53 canyon slope 

(SW-face), deep 

soil 

7 37+ 4l canyon slope 

(NE-faoe) 

8 41+ 55 riparian oanyon 

floor 

desert shrubs, columnar 

cacti, other succulents 

thornscrub - desert 

trees and shfeubs; rich 

succulent growth 

thornscrub, desertscrub; 

shrubs, small 

trees 

riparian thornscrub; 

trees, palms, shrtbs, 

vines

9 

10 

11 

12 

13 

1*1. 

15 

16 

17 

6 

7 

19 

37 

36 

46 

43 

16 

20 

21 

40 

51 

49 

48 

TABLE 6?—Continued 

Bahia San Pedro 

lower beaoh 

upper beach 

crest of low 

beaoh dune 

rooky hill 

(S-face) 

rooky pediment 

(low NW slope) 

floodplaln 

narrow, rooky 

canyon bottom 

Isla San Pedro Nolasco 

16 

20 

steep slope 

(N-face) 

steep slope 

(E-face), ca« 

140 m. elev. 

salt grass: Sporobolus 

vlrglnlous 

salt grass, Croton 

oallfornlous 

salt grass* Croton 

oallfornlous. small 

desert shrubs 

small desert shrubs 

mixed desert shrubs, 

Acacia wlllardlana. 

Fouqulerla diguetll 

low fores of Lyslloma 

Candida 

thornsorub - riparian 

desert shrubs 

meadow of grasses 

and forbs 


cacti (columnar, 

prickly pear, dwarf, 

globose)

18 

19 

20 

21 

22 

23 

24 

14 

19 

17 

25 

Continued. 

steep slope 

(E-face), ca. 

2?0 m. elev. 

steep slope 

(W-face), ca. 

275 elev. 

crest of island, 

ca. 300 m. elev. 

i Ba.1a 

top of high 

beach dune 

saline flat, 

ca. 1 km. 

inland 

low sand hummocks, 

ca. 1*5 

km. inland 

desert plain 


cacti (columnar, 

prickly pear, dwarf, 

globose) 


oaoti (columnar, 

dwarf globose) 


cacti (oolumnar, 

cholla, dwarf globose) 

desert shrubs, succulents. 

Allenrolfea 

occidentalism Croton 

californlcus. Euphor 

bla leuoophvlla 

Frankenla palmerl. 

AllenrojTea Occident 

alls 

cardonal1 columnar 

cacti, cholla, mixed 

desert shrubs, Frank 

enla palmerl 

mesquital; mixed 

spinose desert 

trees and shrubs

25 

26 

27 

28 

29 

30 

31 

32 

3^ 

26 

15 

33 

24 

33 

20 

30 

13 

23 


Ensenada Blanca. Isla Tlburon 

28 

17 

37 

25 

33 

rocky hill near 

shore (W-face) 

mesa, desert 

pavement 

canyon bottom 

steep rocky 

slope (S-faoe) 

steep rocky 

slope (N-face) 

Palo Flerro. Isla Tlburon 

20 

3^ 

14 

23 

ridge-orest 

sandy swale 

between ridgecrests 

open sandy flat 

near shore 

lower edge of 

middle bajada 

Frankenla palmer!. 

Atrlplex""barclayana 

Atrlplex barclayana. 

Fagonla pachyacantha 


Atrlplex barclayana 

Jatropha cuneata. 

Larrea dlvarlcata. 

Atrlplex barclayana, 

desert shrubs 


Atrlplex barclayana. 

Fagonla""paohyacantha 

Frankenia palmeri 

columnar cacti, mixed 

desert shrubs 

Frankenla palmeri. 

Fououierla splencTens 

Larrea divaricate. 

Cordla parvlfolia, 

mixed desert shrubs

TABLE 67 —Continued 

35 25 30 middle bajada mixed desert shrubs, 

small desert trees 

36 34 40 middle bajada, 

streamways 

Sauzal. Isla Tiburon 

37 21 23 low hill or 

hummock 

38 27 30 low hill or 

hummock 


small desert trees 

Eneella farlnosa. 

Larrea dlvarlcata 

Enoelia farlnosa. 


39 32 34 rooky hill 

(N-face) 

desert shrubs 

40 28 30 steep rocky 

hill (S-face) 

desert shrubs 

41 38 45 floodplain small desert trees, 


Central Valley. Isla Tiburon 

42 16 16 valley plain Larrea divaricata 

43 36 39 valley plain, 

ex-floodplain 


44 31 39 arroyo margin desert trees, mixed 

desert shrubs 

^5 31 32 rocky slope (Eface), 

ca. 300 

m. elev. 

mixed desert shrubs

46 34 38 

47 

48 

49 

50 

51 

52 

53 

54 

16 

20 

34 

29 

26 

26 

24 

16 


rocky slope (E- Acacia wlllardlana. 

face), oa. 450 mixed desert shrubs 

m. elev. 

Tecomate. Isla Tlburon 

17 

24 

38 

34 

27 

valley plain 

valley plain, 

near floodplaln 

bench adjacent 

to floodplaln 

floodplaln 

low rocky hill 

(NEB slope) 

Isla San Esteban 

29 floodplaln 

28 

16 

rocky slope 

(E-face) 

rooky slope 

(S-faoe) 

Larrea dlvttrloata. 

Encella farlnosa 


Enoella farlnosaT 


small desert trees, 


desert trees, mixed 

desert shrubs 


Jatropha ouneataT 


Paohycereus prlnglel. 

Olneya tesota, mixed 

desert shrubs 

mixed desert shrubs. 

Agave dentlens, small 

cacti 

Jatropha ouneata. 

Hlblsous denudatus. 

few desert shrubs, 

oaotl, Agave dentlens

57 

58 

59 

60 

6l 

62 

63 

64 

17 

23 

31 

33 

30 

6 

14 

15 


Santa Bosa (mainland) 

20 

27 

39 

*3 

32 

7 

22 

14 

lower bajada 

Lower-middle 

"bajada 

middle bajada 

upper bajada 

low rocky hill 

(SW-face) 

Sargento 

lower bajada 

middle bajada 

upper bajada 

Frankenla palmer1 




Pachycereus prIngle1. 


Franserla dumosa, 


Pachyoereus prlnglel. 

small desert trees, 



Ceroidium mlorophyllum 


Pachycereus prlnglel. 

Ceroidium mloropnyllum* 


Larrea dlvarlcata 

Pachycereus prlnglel. 

Jatropha cuneata. 

Larrea dlvarlcata

TABLE 67-—Continued 

20 

19 

low rooky mesa 

In upper bajada 

low rooky hill 

(S-face) 

Fougulerla splendens. 


Larrea dlvarloata 


desert shrubs

2» 26, 37, ^2, 47» and 62 to 66). Communities with similar 

numbers of speoies per unit area also tend to resemble eaoh 

other in other respeots. 

Shore communities, ©•£•» mangrove or estero, strand, 

373 

and ooast shrub (Frankenla palmer1) communities (£•£•• Tables 

1» 9> 10» 21, 56, 57* and 62) are relatively simple and 

characteristically contain fever speoies than nearby areas 

inland from the shore, and at slightly higher elevations. 

In general the vegetatlonal gradients show trends of increas 

ing numbers of speoies away from the shore. This trend is 

especially evident across the relatively even and gradual 

environmental gradients at Santa Rosa on the mainland side 

of the Infernlllo (Tables 57 to 6l, and 67). Quadrat studies 

at Bahfa San Carlos and Bahfa San Pedro (Table 67* and else 

where) also reveal this pattern. 

Riparian and semi-riparian habitats (£•£•» Tables 

3, 8, 14, 15» 27, 41, 43, and 44), for nearly every oase 

investigated, support greater numbers of speoies in the 

quadrat area or community stand than in adjacent or nearby 

non-riparian habitats. Several paired quadrats, riparian 

and non-riparian (e.g., Tables 2 and 3, 42 and 44), show 

this relationship to be a strong one. South- and west- 

facing slopes (e.g., Tables 19» 25» 28, 40, and 54) gener 

ally support fewer numbers of speoies than east- and north- 

facing slopes whioh may be presumed to be less xerlo («.•&•» 

Tables 29» 39. 53* and 46).

Slopes and ridges or level terrain exposed to desio- 

oatlng winds (e.g., Tables 5» 16, and 26) typically support 

fewer numbers of speoles than similar but sheltered habitats 

(&•£*» Tables 6 and 25) • Thus the exposed north-facing 

slopes on Isla San Pedro Nolasoo (Table 17, Fig. 22), and 

Isla Aloatraz (p. 1*8) support communities of few species 

and generally low-growing wind resistant plants* Soil 

depth, structure, runoff, and other factors generally influ 

encing soil moisture also affect the riohness of vegeta 

tion and numbers of species present* Thus the number of 

species present is directly influenced by the quantity and 

duration of plant-available moisture* Soil moisture is 

generally the primary controlling factor although atmos 

pheric moisture (i.*e*, dew and fog) is, in some oases, of 

obvious importance* 

The maximum number of species occurring in any one 

quadrat and community stand is summarized in Table 67 and 

shown In Fig* 86 for the mainland regions and four islands* 

The similarities in community species numbers are signific 

ant with the highest values occurring in regions with rela 

tively mesio habitats* Thus there is a general trend of 

rioher communities towards lower latitudes and on larger 

Islands* Isla San Esteban and Isla San Pedro Nolasco 

show marked reduction in number of speoles per unit area, 

as compared with the nearest larger land masses, while 

37*

Figure 86* Maximum number of speoies occurring in quadrats 

(solid bar) and in community stands (open bar) 

at the study areas on the major islands and 

mainland regions of the Gulf Coast* Data in 

Table 6?«

Vt 

3 [ Sargento- 

Isla Datll, essentially a fragment of Isla Tlburon* sup 

ports communities nearly as rich as those sampled on Isla 

Tlburon. The lower speoles numbers ooour for relatively 

arid regions (e*g*t Llanuras and Sargento) and Islands 

($*£•» Isla Esteban and Isla San Pedro Nolasco); Insu 

376 

lar Isolation Itself does not appear to be the major causa 

tive faotor In the distribution of species or speoles groups 

on the Gulf Islands of Sonora. The five primary study areas 

on Isla Tlburon show similar numbers of species and the minor 

variations are consistent with apparent moisture conditions* 

Thus EnBenada Blanoa and Teoomate9 at the arid west side of 

the Island are slightly poorer In numbers of speoles per 

community or area than the east and Interior parts of the 

Island* The sharp decrease In number of species at the 

north end of the Infemlllo region (Sargento) Indicates 

locally arid conditions. There are strong Indications 

that the vegetation from the Sargento locality In the 

vicinity of Cerro Tepopa and northward along the Sonoran 

coast Is relatively more xerophytlc than the remaining 

Gulf Coast regions at lower latitude* However, a local 

paucity of ephemerals at the Sargento study area during 

the year of sampling (19^5) may be a contributing faotor 

to the low number of species recorded here* 

The number of phanerogam species now known for each 

of the major Sonoran Islands In the Gulf of California Is

summarized in Table 68 and the data graphed in Fig. 87. 

Additional species from the islands will unquestionably be 

enoountered with further exploration* Values given for 

the island area have been taken from several sources 

(Gentry, 19^91 Tamayo, 19^9» USN Ocean. Office, 1951) and 

are modified in aooordance with my observations. The val 

ues given are approximate to varying degrees, and should 

not be taken as exact although the relative positions seem 

to be correct. 

The relationship between number of species and 

island size gives an expeoted high positive correlation 

coefficient (r • +0.812, P «

TABLE 68 

NUMBER OF SPECIES AND AREA OF SONORAN ISLANDS IN THE GULF 

OF CALIFORNIA 

Area Number of 

Island (sq. kma) Species 

Tiburon 1200 260 

San Esteban 35 87 

San Pedro Nolasoo 3.0 51 

Aloatraz 1.0 38 

San Pedro Martir 1.0 25 

Datil 0.5 83 

Patos 0.3 9 

Cholludo 0.1 26 

378

Figure 87. Regression of numbers of species (vascular 

land plants) on total area for the Sonoran 

islands in the Gulf of California* Data from 

Table 68.

300 

'o 100 

380 

offer an attractive hypothesis to explain the observed low- 

speoies-area relationships. However, Insular isolation is 

here inseparable or closely associated with aridity, and to 

a lesser degree also with comparatively less eoologio (or 

topographic) diversity, and these seem to be major factors 

influencing richness of flora. 

Life-form 

Life-forms or growth-forms in the Sonoran Desert 

are classified and discussed by Shreve (19*12, 1951), and 

Whittaker and Niering (1964). The life-form classifica 

tion presented below for the Gulf Coast of Sonora, is based 

on the gross physiognomy and habit of the plant and as suoh 

is roughly comparable to the well known and classic life- 

form classification of Raunkiaer (193*0- 

1. Trees. 

2. Large shrubs or small trees 

3. Medium shrubs 

Vines 

5. Large succulents 

6. Medium succulents 

7. Small succulents 

8. Small perennials 

9. Annuals 

o 

H 

Hydrophytes 

.

11* Epiphytes 

12. Root perennials 

381 

The distribution and variation in life-forms in the 

Gulf Coast of Sonora as represented by the Guaymas region, 

Isla Tlburon, Isla San Esteban, and Isla San Pedro Martlr 

Is given in Table 69 and diagrammed in Fig* 88. The values 

for each life-form olass represent the percent of species 

of the total flora at eaoh island and region indicated* 

Trees.—Trees are here defined as arborescent 

foliage-bearing plants oommonly exceeding 6 m. in height. 

A few species develop into trees on the mainland and Isla 

Tlburon but this olass, as here defined, is entirely absent 

from the remaining islands. North of the Guaymas region 

the number of species developing into trees and the popu 

lations drop off appreciably. For the most part trees in 

the Gulf Coast are concentrated along riparian and semi- 

riparian arroyos and canyons. Dioot trees and palms 

constitute the two major tree forms in the Gulf Coast. 

Flcus, with three species (Appandlx A), includes 

the most massive and tallest dioot trees in the Gulf Coast. 

Flcus radullna. which I have found In the Gulf Coast only 

at Cation Nacapule, Is unique to the Gulf Coast in the pos 

session of buttressed roots, whioh are relatively small 

buttresses compared with trees of troploal climates but 

clearly evident. This large tree of definitely troploal

TABLE 69 

DISTHIBUTION OF LIFE-FORMS IN GULF COAST OF SONORA 

Life-form Percent of Species 

San 

# San Pedro 

Guaymas Tlburon Esteban Martlr 

Trees 2.6 1.0 0 0 

Small trees or 

large shrubs 12.2 9.1 1.7 4.0 

Medium shrubs 2 6.6 29.7 31.6 29.1 

Vines 3.9 3.1 1.1 0 

Large succulents 1.5 1.9 3.^ 4.0 

Medium suooulents 5.1 2.7 2.3 4.0 

Small suooulents 5.7 2.7 3.^ 0 

Small perennials 18.4 20.1 25.9 20.8 

Annuals 19.0 27.0 30.5 37.5 

Hydrophytes 1.8 1.5 0 0 

Epiphytes 1.8 0.8 0 0 

Hoot perennials 1.2 0.4 0 0 

382

Figure 88* Life-form speotra on islands and Gulf Coast 

of Sonora.

} 

12 3 4 1234 1234 1234 

Trees Large Medium Vines 

Shrubs Shrubs 

Guaymas Region 

Isla Tiburon 

Isla San Esteban 

Isla San Pedro Martir 

2 3 4 12 3 4 

Large Medium 

Succulents 

1234 1234 1234 

Smally Small Annuals 

Perennials 

Hydrophytes 

VL 

12 3 4 12 3 4 

Epi— Root 

phyles Perennials 

GJ 

00 

OJ

384 

appearance Is otherwise known in Sonora only from riparian 

short-tree forest canyons in the mountains of subtropioal 

southeastern Sonora (Gentry, 19^2). 

Floua palmerl. with a wide facultative variation 

in size, is the most widespread of the larger Gulf Coast 

trees. It is far more readily drought-deciduous than its 

other Gulf Coast oongeners, both of whioh have very limited 

ranges in the Gulf Coast. Flcus palmerl and Bumella Occi 

dent alls are the only larger tree species occurring on Isla 

Tlburon. Truly large individuals of both species are 

uncommon and widely soattered through the more favorable 

portions of the interior of the island. In the interior 

canyons and valleys in the Sierra Kunkaak range individual 

Flcus palmerl may reach 15 to 20 m. or more in height. 

Other dicot trees in the Gulf Coast include Celtls reti 

culata and Saplndus saponarla. The larger Individuals of 

several leguminous trees often exceed 6 m. and may be 

classed as trees, e.g., Acacia wlllardlana. Lyslloma 

dlvarloata. and Prosopls torreyana. 

Three genera of palmate (fan) leaved palms, each 

represented by a single species, occur in the Guaymas 

region. The relative paucity of trees in the Gulf Coast, 

particularly on the islands other than Isla Tlburon, 

reflect the overall aridity of the region.

Small Trees and Large Shrubs.--Included In the 

class of small trees or large shrubs are woody speoles 

whioh commonly reach 2.5 to 6 m. tall* Characteristic 

genera in the Gulf Coast include Cercldlum. Bursera. For- 

chammerla. Fouaulerla. Jacqulnla, and Zlzyphus. Some 

species in this class occasionally or regularly develop 

multiple trunks or stems, e.£., Cercldlum mlcrophyllum. 

Colubrlna glabra. Coursetla glandulosa. Pithecoloblum 

sonorae. and Vallesla balleyana and V. glabra. Others 

with well defined "but often short trunks may variously "be 

385 

considered to "be small or dwarf trees, £•£•» Bursera micro- 

phylla. Forchammerla watsonll. Guaiaoum coulterl. and 

Jacqulnla pungens. This class is present on every island 

exoe~* isla Patos (presently and before 19^6, see p. 351 )• 

The number of species, percent of species, and population 

density of the large shrub and small tree elements dwindle 

towards the northern part of the Gulf Coast and onto the 

smaller and more arid islands. A single species, Flous 

palmerl« gives a value of for this class on Isla San 

Pedro Martir. 

Medium Shrubs.—Medium size shrubs constitute one 

of the three most common, ubiquitous, and often dominant 

life-forms throughout the Gulf Coast of Sonora. These 

are woody or semi-woody perennials which are oommonly 

0.5 to 2.5 m. tall. The olass is made up largely of the

common Sonoran Desert desertscrub species, £•£•» Berglnla 

vlrgajba, Cordla parvlfolla. Encella farlnosa. Jatropha 

386 

cuneata. and Viscalnoa genlculata. Many of these sometimes 

exceed 2.5 but I have attempted to consider the most com 

mon height for the populations. In comparing populations 

on the various regions and islands the same species may 

variously fall into more than one class* For example, 

Bursera mlcrophylla and Prosopls torreyana are faoultatlve 

small to medium-size shrubs on arid Isla Alcatraz; but else 

where the same species commonly become large shrubs and 

occasionally Prosopls develops into a tree over 6 m. tall. 

In placing a species or population in one class or another 

I have arbitrarily put the woodier borderline cases into 

the larger size class, and the less woody or herbaceous 

and semi-herbaceous ones into the smaller size class. 

Succulents (Large).—The suooulent species are 

divided into three major size classes: large, medium, and 

small. The larger succulents in the Gulf Coast consist 

wholly of arborescent and semi-arborescent stem succulents. 

These are oereold Cactaoeae in the following genera: 

Carneglea. Lemalreocereus. Lophocereus. Machaerooereus, 

and Paohycereus. Pachycereus prIngle1 is one of the larg 

est and most massive succulents in the world. It is the 

largest common terrestrial organism and one of the most 

conspicuous and characteristic elements along the shores

of the Gulf of California. On the Gulf Coast of Sonora 

it occurs from Puerto Libertad to a short distance south 

of Guaymas, and on every island; it occurs over a major 

portion of Baja California (Shreve, 1951)# Certain indi 

viduals of Picus in the Gulf Coast may exceed Paohycereus 

prlnglei in total weight but they are uncommon, and little 

known. 

Suoculents (Medium).--Several growth-forms repre 

387 

senting various families comprise this class. The relative 

number of species of medium sized succulents and diversity 

of growth-forms is greater in the Guaymas region (5*1$) 

than elsewhere in the Gulf Coast (2.3-4.0#)• A major dis 

tinction may be made between stem and leaf succulents. For 

the most part the medium sized stem succulents are aphyllous 

or essentially so, ©•£•» Caotaceae (except Peresklopsls). 

and Allenrolfea oocldentalls. Euphorbia ceroderma, the 

only cactoid Euphorbia in the Sonoran Desert, has small 

and quickly drought-deciduous leaves and thus closely 

approaches the aphyllous habit. 

Growth-forms among the cacti consist largely of 

phylogenetically related taxa, i Cyllndropuntla 

(oholla), Platyopuntla (prickly pear), Ferrooactus (barrel 

cactus or vlsnaga), Wllcoxla and Penlooereus. and Pere- 

sklopsls. Species of cholla are in every region and on 

each of the islands of Sonora they are generally common.

A few speoles, e.g., Opuntla fulglda. may occasionally 

exceed 2.5 m* In height In the Gulf Coast* However, 

further Inland and northward these same speoles commonly 

reaoh muoh greater heights and become seml-arboresoent, 

as In Arizona and northern Sonora• 

The prlokly pears are surprisingly scarce in the 

Gulf Coast. Two speoles of Platyonuntla have been found 

In the Guaymas region, one of whloh also ooours on Isla 

San Pedro Martlr, and a third speoles ooours on Isla 

Aloatraz. This flat oaotold growth-form Is usually 

restrloted to east-facing slopes In the Gulf Coast and Is 

388 

absent from sites whloh are arid In the extreme. The rela 

tive abundance of cholla In the Gulf Coast and the paucity 

of prlokly pear with Its restriction to comparably less 

xerlo exposures Is partly explainable In terms of the 

surfaoe-volume relationships. Beduoed surface-volume 

ratio has been demonstrated to be an adaptation to xerlo 

conditions In the Sonoran Desert (Felger, 1966). The 

narrow-elllpsold cross-section area of the prlokly pear 

presents greater surfaoe-volume ratio than does oholla 

with an essentially cylindrical cross-section. 

Peresklopsls porterl Is both a leaf suoculent and 

stem succulent, although the leaves are drought-deciduous. 

It Is a slender-stemmed, seml-vlnlng plant whloh ooastally 

reaches Its northernmost limit near Bahfa San Carlos. Here

it is restrioted to dense and brushy thornsorub-1Ike 

arroyo margin communities. 

Leaf suooulents falling into this class (medium- 

sized succulents) include several species of larger-leaved 

Agave* These are mostly confined to relatively favorable 

habitats, e.g., mountain slopes and oanyons rather than in 

open desert situations. Thus, as with the prickly pear, 

Agave ohrysoglossa is oonfined to east-facing slopes on 

Isla San Pedro Nolasco (Figs. 23 and 24) and the opposite 

mainland. A population of Agave on Isla Tiburon, closely 

389 

related to A. ohrysoglossa. is also confined to east-facing 

slopes. 

Succulents (Small).—Small succulents include 

several growth-forms of plants generally less than 0.5 m. 

in height. The number of species of small suooulents and 

their distribution in the Gulf Coast are in many respeots 

similar to the medium size ("shrub") suooulents (Table 69, 

Fig. 88). The absence of small succulents from Isla San 

Pedro Martir, Isla Patos, and Isla Aloatraz may be related 

to the greater exposure and extreme aridity of these 

islands. Small suoculents are present and generally com 

mon on other small and much less arid islands, £•£•, Isla 

Datil, Isla Cholludo, and Isla San Pedro Nolasoo. 

Small succulents may be classified into growth- 

forms much the same as the larger succulents. Small stem

succulents include Echlnocereus. Mammlllarla. Opuntla 

marlnae, and Sallcornla. Aoaulescent leaf succulents are 

represented by Heohtla montana and several small species 

of Agave. Herbaceous perennial succulents with succulent 

leaves and stems include several halophytic species, £•£•* 

Abronla marltlma. BatIs marltlma. and Sesuvlum portula- 

oastrum, and a few cliff-dwelling composites, e.£., Hof- 

melsterla crasslfolla and H. fasclculata. 

Many other species in the Gulf Coast possess semi- 

succulent stems and/or leaves and may variously be classed 

as succulents. For example species with semi-succulent 

leaves Include Atrlplex barclayana. Lyclum spp., Maytenus 

390 

phyllantholdes. Rhlzophora mangle, Stegnosperma hallmlfolium, 

and Suaeda torreyana: and species with semi-succulent stems 

or trunks include Ascleplas albicans, A. subulata, Bursera 

mlcrophylla, and Suaeda torreyana. The leaves of some 

xerophytic Gulf Coast perennials initially may be only 

semi-succulent or non-succulent and with age develop into 

thickened and markedly succulent structures, e, Lyclum 

spp., Maytenus phyllantholdes, and Vlscalnoa genlculata. 

l Perennials.—The broad and general class of 

small perennials Includes dwarf shrubs and suffrutescent 

or partially suffrutescent plants commonly less than 0.5 m. 

tall, most perennial grasses, and miscellaneous perennial 

herbs. These plants, representing a large percentage of

the flora (18.^-25^) show little consistent variation from 

region to region. Raunklaer's (193 1 *) life-form olasses of 

chamaephyte and hemicryptophyte are approximate for the 

species included here as small perennials. The major 

orlterion employed for determining chamaephytes and hemi- 

cryptophytes, i,»e.t position of the terminal merlstem in 

relation to winter protection (snow cover, leaf litter 

cover), is scarcely applicable here. Even arbitrary 

delimitation of these classes In the Gulf Coast is not 

391 

enhanced by setting up an intermediate class (cf. Whlttaker 

and Nlerlng, 196*1-, p. 12). 

Perennial grasses may be segregated from others in 

this class (small perennials). 1 have, however, chosen to 

include them here with the other small perennials because 

other grasses («•£• > annual grasses and shrubby perennials 

grasses) as well as other monocots (£•£•• palms) are not 

elsewhere segregated into separate classes in the present 

system. Common examples of small perennial grasses include 

the perennial species of Arlstlda. Andropogon. Setarla, and 

Trlchachne. The salt grasses, Jouvea pllosa. Sporobolus 

vlrglnlcus. and Monanthochloe llttoralls. growing along the 

beaches and estero margins, form a distinctive group of 

harsh-leaved halophytic species. Non-halophytic perennial 

grasses are relatively uncommon In the Gulf Coast of Sonora 

and seldom form an important element of the landscape.

The dlcot species of small perennials represent a 

broad span of growth-forms. The individual species often 

do not adhere to a single growth-form and In the present 

study they are not further divided* Common small dloot 

perennials are represented by the following examples! 

Alllonla lncaraata 

Atriplex barclavana 

Cassia "coves!! 

Cressa truxlliensIs 

Elytrarla lmbrloata 

Euphorbia albomargTnata 

Fagonla spp. 

Frankenla palmer! 

Franserfa spp. 

Hoffmanseggla lntrloata 

Lyrooarpa ooul temper! 

tylepalmer! 

392 

Annuals* —This class Is Identical with Baunklaer's 

(193*0 therophyte life-form* It Is one of the larger life- 

form classes In the Gulf Coast (19-37*5$) with a well 

marked trend of Inorease toward the north and onto the 

smaller and more arid lslandB (Table 69» Fig* 88)* The 

distinction between ephemeral and annual life-form In the 

Sonoran Desert Is emphasized by Shreve (1951) and the 

majority of these species In the Gulf Coast of Sonora are 

ephemerals. This distinction Is oertalnly valid and quite 

useful when studying Individuals and local populations, 

but often breaks down when categorizing species* As a 

consequence the term annual here Includes both ephemerals 

and the very few true annuals* For example, Coreocarpus

SPP.. Cryptantha fasolculata (see Johnston, 192**), and 

Euphorbia pedloullfera may exist as typically short-lived 

ephemerals, true annuals, or short-lived perennials* 

Ephemerals in the Sonoran Desert may be grouped 

into three broadly intergrading physiological classes: 

winter-spring species, summer-fall species, and non- 

393 

seasonal species. The genetically controlled physlologioal 

differences between species responding to summer (warm 

weather) rainfall and the winter-spring species are dis 

cussed by Edith Shreve (1923)* The groups of speoles 

limited to periods of adequate soil moisture following 

precipitation during winter and early spring are represented 

by the following examples: 

Aohyronyohla cooperl 

Andraohne clllato-glandulosa 

Antirrhinum costaturn 


De s curalnla~pinna ta 

Dyssodla conolnna 

Nlcotlana Cleveland!! 

Oenothera leptocarpa 

Phacelia mlnutlflora 

Tlllaea ereota 

Cryptantha fasolculata* termed a "long-lived annual" 

by Johnston (192*0, is one of the few species of annuals 

which Is able to survive from early spring through the pre- 

summer rainfall drought. Several annual speoles of 

Erlogonum in northern Sonora, E. deflexum, commonly 

show such a phonological pattern but none reaches the area 

of the present study. Cryptantha fasolculata apparently

germinates only during the winter-spring rainfall season* 

as is characteristic of its other oongeners in the Sonoran 

Desert; and although it sometimes survives through the 

summer-fall season it does not germinate during that 

season. A similar oase has been observed with Camissonia 

oardlonhvlla in the Pinaoate region at the head of the 

39* 

Gulf • although on Isla San Pedro Martir and on Is 1A Tlburon 

this species appears to remain striotly a spring ephemeral 

and does not survive beyond April. For the most part Gulf 

Coast winter-spring ephemeral# show relatively close phylo- 

genetio relationship with taxa of the more extensively 

developed winter-spring flora in the northwestern part of 

the Sonoran Desert and other deserts of predominantly 

winter-spring rainfall regimes* In this respect these 

species differ from the common biogeographio pattern of 

the majority of taxa in the Gulf Coast of Sonora, which 

are derived from subtropical biota now found predominantly 

at lower latitudes. Many winter-spring ephemerals in the 

Gulf Coast have ranges extending into other Horth Amerioan 

deserts (Shreve, 1951) and here reach their southernmost 

limits for North America. 

Ephemeral species responding only to summer and 

early fall rainfall oharacteristloally exhibit affinities 

with taxa in subtropical regions and generally south of 

the Sonoran Desert. These subtropical taxa from which

the aummer-fall group la derived are generally perennial 

speoies (see Low®, 196**, p. 19)* Gulf Coast speoies 

oharaoteristioally Halted to hot-weather precipitation 

are typified by the following examplest 

Kallstrosmia spp. 

Panloua arlzonloum 

Panloum hlrtloaule 

Portulaoa lanoeolata 

Setarla flebmannll 

gnorobolus patens"" 


TrlbulusTerrestri s 

395 

Certain speoies oommonly United to the summer-fall season, 

• Aaaranthus flabrlatus. Boerhaavla SPP., and Peotls 

uapposa. sometimes ooour, though weakly so, onoe again 

following winter-spring rainfall. In comparison with the 

summer-fall populations, they are generally auoh reduoed 

in density and the individuals are often feeble and dwarfed* 

Suoh plants, when found, are often on looally warm sites 

suoh as southwest-faolng slopes and following unseasonably 

warn weather. Bouteloua barbata and B. arlstldoides usu 

ally show maximum development during the summer-fall season. 

They may also ooour in the spring with warm weather but 

seldom approach maximum density at suoh time and the plants 

are often relatively dwarfed. 

Due to high temperatures, summer speoies respond 

with rapid germination to the oommenoement of the summer 

monsoon, generally during July. During the past several 

years on the Gulf Coast I have observed these summer

thunderstorm rains to drop off or oease for several weeks 

or more, late in the season, often in September and early 

October, and to resume temporarily before the onset of low 

temperatures| suoh rain is often derived from hurrioane- 

fringe storms* Beoause of the high transpiration rates 

at this time of year, a lull in precipitation quiokly 

brings about extensive wilting and die-baok, and many 

ephemerals may perish altogether* Resumption of rainfall, 

while temperatures are still high, allows rapid develop 

ment of new growth and germination of a new generation. 

These plants may overlap the winter-spring species* The 

populations germinating as a result of late Ootober or 

November rains, when suoh rainfall ooours, are oomprised 

of different proportions of speoies than the first wave of 

summer ephemerals resulting from the July onset of the 

monsoon* 

Roughly one-third of the ephemeral speoies in the 

Gulf Coast of Sonora are non-seasonal and germinate subse 

quent to adequate rainfall at any time of the year* In 

general the non-seasonal ephemerals are more extensively 

developed toward the southern part of the Gulf Coast of 

Sonora and least developed in the north* My observations 

Indicate that non-seasonal ephemerals gradually decrease 

into the northern and more arid parts of the Sonoran 

Desert* It appears that a significant reduction of 

396

non-seasonal ephemerals ooours just north of the present 

study area in the vioinity of Cerro Tepopa and Oesenboque 

San Ignaolo. A few oommon non-seasonal ephemerals In the 

Gulf Coast ares 


" aerl 

Dalea mollis 

lor 

jiffgorfrla polyoarpa 

Hentzella adhaerana 

Perl tyle""emoryl 

'Fhaseolus flllformls 

33nspeteleia rupestrls 

397 

There are varying degrees of lntergradatlon between 

non-seasonal and seasonal olasses* Some speoles, e.g., 

Antirrhinum ovathlferum. are truly non-seasonal and appear 

to be dependent solely on the prevailing soil moisture, 

without thermoperiod or photoperiod limitations in this 

region* Others are similarly non-seasonal but their maxi 

mum development may, to varying degrees, be seasonal* 

Mild winters in the Gulf Coast allow taxa, whioh are else 

where assoolated with vernal preolpltation, to develop here 

in the winter, e*£*, Amaranthus watsonll and Cenohrus 

palmer1. Amaranthus is oharaoterlstloally a summer-fall 

growing annual or ephemeral (see Sauer, 1955) • However, 

watsonll. a Gulf of California segregate of the wide 

spread A. palmerl. Is oommon during winter-spring and 

summer-fall seasons* It is sensitive to freezing or

near-freezing temperatures and extensive oold injury or 

mortality ooours after one or more days of suoh weather• 

If the plants are not killed and sufficient soil moisture 

remains, recovery is rapid following the return of warm 

weather. In the winter and spring the larger populations 

of this speoies are usually found in somewhat protected 

and warm sites* Minimal temperatures thus appear to be 

limiting for these plants. Euphorbia setlloba is dis 

tinctly limited by oold weather but is otherwise non- 

seasonal. Several successive generations may develop and 

persist through the summer-fall season and into the begin 

ning of the winter rainfall season. If freezing or. near- 

freezing weather ooours, usually in late Deoember or early 

January, the plants are killed. If rainfall ooours again 

398 

later in the same season, e.g., in February, after freezing 

or generally low temperature weather has largely passed, 

germination and rapid development will follow. 

Other species may respond to day length, although 

not so markedly as certain striotly seasonal species. 

Perltvie emoryl has been collected during both of the 

rainy seasons, but it is seldom present with the first 

generation of summer ephemerals. It has been found, how 

ever, in large numbers toward the end of the summer, in 

the latter part of August and in September. Extreme and 

mean temperatures are oertalnly not signifioantly lower,

in this regard, at that time* Day length, however, Is 

changed, and photoperlod may be an important physloal 

oontrol. 

Epiphytes*—Epiphytes in the Gulf Coast of Sonora, 

representing only six species, are comprised of two dis 

tinctive habits of growths parasitlo and non-parasitlo. 

The Loranthaoeae oomprlse the parasitlo epiphytes with 

four species in three genera. Although parasitlo plants 

are only indirectly dependent upon soil moisture, leaf- 

size and number of species are greatest in the regions 

with relatively mesio habitats. Thus all four species 

are present in the Guaymas region and the numbers are 

fewer northward and into more arid regions. The widest 

ranging and most xerophytio species, Phoradendron oall- 

fornicum. has minute scale leaves and is functionally 

aphyllous while the remaining ones, generally occurring 

in less arid habitats, possess well-developed leaves. All 

of the Gulf Coast Loranthaoeae have semi-succulent leaves 

and most have partially fleshy stems. 

Non-parasitlo (or true) epiphytes are represented 

by only two species of Bromellaoeae, Tlllandsla exserta 

and T. recurvata. Non-parasitlo epiphytes are character 

istic of tropical and subtropical regions and reach their 

northern limit for the west coast of Sonora in the vicin 

ity of Guaymas. 

399

Hydrophytes.—Speoies growing in fresh watert with 

at least the roots and the lower portion of the shoot sub 

merged » are here olassed as hydrophytes* Fully submerged 

fresh-water vascular plants are not known in the Gulf 

Coast* Hydrophytes are poorly represented in the flora 

(maximum of 1.8^) and are narrowly restricted to the few 

fresh water habitats to be found in the Guaymas Honadnook 

and on Isla Tiburon* 

Small and relatively short-lived hydrophytes may 

tfOO 

be annuals, e*g., Eleooharls genioulata and Cyperua eleaans. 

The plants do not die out entirely with only seeds remain 

ing for the next generation as do typioal annuals or thero- 

phytes, and they are therefore not included with annual 

plants* Most of the Gulf Coast hydrophytes are perennial 

although none are woody* The hydrophytes in the Gulf Coast 

are generally wide-ranging speoies with geographic ranges 

far exoeeding the limits of the Sonoran Desert* Examples 

inolude Cyperua esoulentua. Pulrena simplex* and Typha 

domlngensls* 

Life-form Spectra on Isla Tiburon and in the Infernillo 

Region 

The life-form spectra at two localities on Isla 

Tiburon, one on the arid west side (Ensenada Blanca) and 

the other in the less xerio interior (oentral valley) are 

shown in Table 70 and Fig* 89* The value for eaoh life-form

TABLE 70 

LIFE-FORM DISTRIBUTION AT TWO STATIONS ON ISIA TIBUHON 

Feroent of total speoles in five 

0*1 ha. quadrats at each looallty 

Life-form Central Valley Ensenada Blanoa 

Trees 0 0 

Large shrubs 11*0 1.7 

Medium shrubs 29.7 32.8 

Vines 3.3 0 

Large suooulents 3.3 1.7 

Medium suooulents 2.2 3.^ 

Small suooulents 1.1 1.7 

Small perennials 13.2 15.5 

Annuals 35.2 43.1 

Epiphytes l.l 0 

401

Figure 89. Life-form speotra at EnBenada Blanoa and 

central valley stations, Isla Tiburon.

45 

40 

35 

30 

25 

20 

I 5 

10 

5 

0 

1 

I 2 

arge 

irubs 

l 

Medium 

Shrubs 

i 2 

Vines 

Central Valley 

Ensenada Blanca 

i 2 i 2 

Medium 

J RL 

Succulents 

• 

402 

I 2 12 12 12 

Small Epi- 

Perennials phytes 

Smalls Annuals

is given as the percentage of the total number of species 

occurring in the community stands of five quadrat study 

sites at each of the two localities* The arid conditions 

at both localities are refleoted by the absenoe of trees 

from the quadrat sites. A few very widely scattered trees 

are present, however, outside the five community stands 

included in the quadrat studies at the central valley sta 

tion (see p. 231, Fig, 52). Vines, epiphytes, and large 

shrubs, characteristically indicative of relatively favor 

able moisture conditions, show greater development in the 

central valley than at the west side of the island. A 

corresponding increase in xerophytioeLements, e.g., small 

and medium rather than large succulents, small perennials, 

403 

and annuals, is seen at Ensenada Blanca. Among the remain 

ing classes there is relatively little variation. 

Field observation and the brief community descrip 

tions in the previous seotion clearly indicate that life- 

form spectra may be more highly varied locally between 

different communities than between entire regions. In 

Table 71 and Figs. 90 and 91 the variation and distribution 

of life-form is shown for three distinctive communities at 

the central valley station on Isla Tiburon. In Fig. 90 

each life-form class is represented as percent of total 

species in the community stand whereas in Fig. 91 the 

number of speoies occurring in eaoh class is graphed. At

TABLE 71 

LIFE-FORM SPECTRA OF THREE COMMUNITY STANDS AT CENTRAL 

VALLEY STATION, ISLA TIBURON 

404 

Arroyo Larrea flat E-0lope 

(Table 44} (Table 42) oa. 450 m. 

TTable 46) 

No* % No. % No. % 

Life-form spp. spp. SPP. app. app. spp. 

Trees 1 2.6 0 0 0 0 

Large shrubs 6 15.4 0 0 5 13.2 

Medium shrubs 11 28,2 

* 

1 6.3 10 26.3 

Vines 1 2,6 0 0 1 2.6 

Large shrubs 1 2.6 0 0 2 5.3 

Medium shrubs 0 0 0 0 2 5.3 

Small succulents 0 0 0 0 1 2.6 

Small perennials 5 12.8 0 0 4 10.5 

Annuals 14 35.9 15 93.8 13 34.2 

Epiphytes 0 0 0 0 0 0

Figure 90* Life-form spectra of three communities at 

oentral valley station, Isla Tiburon.

16 

12 3 12 3 12 3 

Trees Large Medium 

Shrubs Shrubs 

1 V/J7A Arroyo 

2 Plain 

3 Slope (East Facing) 

123 123 123 123 

Vines Lorge Medium Small 

Succulents 

J 

12 3 12 3 

Small Annuals 

Perennials 

0 

01

Figure 91• Life-form speotra of three communities at 

central valley station* Iala Tiburon.

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

I Y////A Arroyo 

2IH Plain 

3 EBBM Slope (East Facing) 

0 a. _ELE EL 

123 12 3 123 123 

Trees Large Medium Vines 

Shrubs Shrubs 

12 3 12 3 

JLarge Medium 

Succulents 

123 12 3 12 3 

Small, Small Annuals 

Perennials

the Larrea dominated, community (see p. 233* Table 42, 

Pig. 53) only two life-forms are present: a medium shrub 

ILarrea dlvarlcata) and 15 species of ephemerals. This 

is one of the simplest non-saline community stands present 

in the Gulf Coast. Both life-forms are characteristic of 

arid conditions and the very high value for ephemerals 

40? 

(93*8$) indicates arid conditions in the extreme (Baunkiaer, 

1934)• The simplicity of this therophytic community 

resembles some of the more arid desert regions in both 

North America (Shreve, 1951) and South America (Morelo, 

1958), where Larrea is the single dominant perennial. 

The life-form spectra of the arroyo margin com 

munity (see pp. 239-242, Table 44, Figs. 52, 54, and 55) 

and the nearby east-facing slope of Sierra Menor (see pp. 

247-250, Table 46, Fig. 57) are essentially similar with 

only few significant differences. Olneya tesota scarcely 

qualifies as a tree here along the arroyo margin community, 

while on the slopes and through most of the region it does 

not exceed the stature of a large shrub. The most appar 

ent contrast between arroyo margin and east slope is the 

relative scarceness of suoculents along the arroyo. 

Life-form distribution at Santa Rosa on the main 

land side of the Infernillo channel is summarized in Table 

72 and graphed in Fig. 92. The number of speoies occurring 

in each life-form class is given for six quadrats placed in

TABLE 72 

LIFE-FORM SPECTRUM ACROSS ENVIRONMENTAL GRADIENTS AT SANTA ROSA, INFERNILLO 

REGION 

Life-form 

Estero 

(Table 5$) 

Number of Species In Community Stand 

Lower 

bajada 

(Table 57) 

Middle 

bajada 

(Table 58) 

Middle 

bajada 

(Table 59) 

Upper 

bajada 

(Table 60 

S-face 

hill 

(Table 6l) 

Large 

shrubs 3 0 3 k 5 1 

Medium 

shrubs 1 8 11 14 11 

Vines 0 0 0 1 2 1 

Large 

succulents 0 1 0 2 2 1 

Medium 

succulents 1 1 k 2 0 

Small 

succulents 3 1 1 1 0 1 

Small 

perennials 3 3 3 2 Ik 5 

Annuals 0 10 8 13 12 12 

Epiphytes JO JO __0 __1 _0 j> 

Total 11 20 27 39 ^3 32

Figure 92. Life-form distribution at Semta Rosa, Infer- 

nillo Region. Distance from estero to south- 

facing slope is oa« 3*5 The numbers on 

the abscissa indicate the table from which 

the data were taken*

tn 

a> 

o 

a> 

Q. 

CO 

a> 

-Q 

E 

14 

12 

10 

8 

6 

4« 

0.^ 

56 

Estero 

/ y 

/ 

57 

Lower 

bajada 

j/ 

/ 

58 

Lower-middle 

bajada 

/ 

S 

Cc* 

s* c \ 

SMJS^ 

u>

a line from the edge of the mangrove oommunity (or estero) 

across the bajada and ending with a small rooky hill at 

the upper edge of the bajada. The environmental gradients 

across the bajada are gradual and there is a corresponding 

gradual shift in life-form* The small perennials are not 

shown in Fig. 92 as there appears to be little or no sig 

kio 

nificant variation. A single species of parasitic epiphyte, 

Phoradendron califoraloum. is present although uncommon here* 

Suooulent plants show the greatest number of species 

in the middle bajada while other bajada life-forms reach 

maximum development at the upper end of the bajada* Sharp 

divergence, and in some oases shift in direotlon of general 

trend, is seen at the estero and on the south-faoing hill- 

slopes* Thus the gradual ohange in life-form composition, 

forming a oontlnuum, shows a trend and rate of shift cor 

responding to the variation of the environmental gradient* 

It is interesting to note that vines and large shrubs,- 

viewed here as representing relatively meslo elements in 

the vegetation, show greatest development with approach 

to the upper bajada. Ephemerals also reach maximum number 

of species at the upper bajada* Although ephemerals consti 

tute 50% of the speoies present in the lower bajada quadrat, 

their population sizes here are relatively small (see p* 

32 5).

SUMMA.BY AND CONCLUSIONS 

Having drawn conclusions at appropriate places 

throughout, major points may he further summarized as 

follows. 

Vegetation on the islands and Gulf Coast of Sonora 

is primarily desertscrub, yet extensive areas of thorn- 

scrub of distinctive subtropioal nature occur on Sierra 

Kunkaak, Xsla Tiburon, and in the Guaymas Monadnook* 

These are surrounded by and broadly intergrade with desert- 

scrub} however* where sharp environmental differences exist, 

desert sorub and thomsorub remain looally dlstinot. 

Pew speoies of plants are endemio to the Gulf Coast 

of Sonora* There are, however, many speoies that occur 

elsewhere only in Baja California* Infraspeoifio diverg 

ence between these vicariads is indioated for a limited 

number of cases* 

While insular endemism among the vascular land 

plants is restricted to a few speoies of small cacti* 

endemism is a conspicuous feature of the mammalian fauna 

and is also evident( although to a somewhat lesser extent, 

in the herpetofauna. The few mammals oocurrlng on the 

smaller islands are, aooordlng to present taxonomy, single- 

island speoies endemios, while those on Tiburon are largely 

Ml

subspecies endemlos* Reptiles, on the other hand, exhibit 

less endemlsm, those on snail islands being distinct 

speoies, subspecies, or not at all distlnot*- Reptiles on 

Tiburon show no deteotable evolutionary divergenoe from 

those on the mainland. 

4X2 

Speoies diversity, in terms of the number of speoies 

of plants per unit area, inoreases from north (desertsorub) 

to south (thomsorub). The low number of speoies per unit 

area on the more isolated islands appears to be primarily 

due to both aridity and the limited eoologio diversity on 

these small islands, rather than to their isolation* 

The prevailing pattern of speoies distribution is 

a continuum* Mosaics ooour Infrequently and only where the 

environmental gradients are sharp and discontinuous* 

The most abundant life-forms in both desertsorub 

and thomsorub are medium-sized shrubs, small perennials, 

and ophemerals. Trees, vines, and epiphytes are especially 

more prominent in thornscrub than in desertsorub communi 

ties. In areas of greatest aridity the suooulents and 

ephemerals comprise the greatest part of both the flora 

and the vegetation; however, their greatest numbers of 

speoies ooour In the most meslo non-riparian desertsorub* 

Floristloally the islands tend to resemble the 

nearest land mass. In contrast, the vegetation of eaoh 

island is distinct and largely dependent on the looal 

envrlonmental conditions*

413 

Pour weakly differentiated phytogeographio regions 

nay be recognizeds (1) the Guaymas region including Isla 

San Pedro NOIASOO, (2) the Llanuras de San Juan Bautista 

and Isla Aloatrar, (3) Isla Tihuron (exolusive of its arid 

west ooast), its satellite islands of Datil and Cholludo» 

and the Infernillo region, and (4) the west ooast of Zsla 

Tiburon, Isla San Esteban, and Isla San Pedro Hartir.

APPENDIX A 

I

APPENDIX A 

DISTRIBUTION LIST OF PLANT SPECIES FOR ISLANDS AND REGIONS 

IN THE GULF COAST OF SONORA 

1, INFERNILLO; £f ISLA TIBURON| D, ISLA DATILf C, ISLA CHOL- 

LUDOj E, ISLA SAN ESTEBAN; A, ISLA ALCATRAZf L. LLANURAS) M, 

ISLA SAN PEDRO MAHTIRj G, GUAXMASj N, ISLA SAN PEDRO NOLASCO 

ACANTHACEAE 

Anlaaoanthus thurberl 

Gray 

Beloperone oalifornioa 

Benth* 

Berglnla virgata Ha nr. 

Carlowrlghtla arizonica 

Gray 

C. oalifornloa Brdge. 

C. oordifolia Gray 

Dioliptera resupinata 

Juss* 

Elytraria lmbrloata 

(Vahl.) Pars. 

Jaooblnla ovata Gray 

Ruellla audiflora 

var. glabrata Leonard 

R. peninsular18 (Rose) Jtn. 

Slphonoglossa long!flora 

(Torr.) Gray 

AIZOACEAE 

Mollugo oerviana (L.) 

Ser. 

Sesuvium verruoosum 

Raf. 


L. 

I T D C E A L M G N 

I 

X 

I 

X 

? 

I 

I 

X 

I 

x 

X 

Z X X 

X ? X 

? 

? X X 

X ? X 

X X 

X X 

? X 

X X X 

X 

X X X X X 

X X X X X 

X X X X X 

X

AMARANTHACEAE 

I T D C B A L M G N 

Aaaranthus fimbriatus 

(Torr.) Be nth. z z x z z z 

A. watsonll Standi. z z z z z z z 

Dioraurus alternlfollus 

(Vats.) Ullne & Bray x 


(Nutt.) Standi. z z z z 

AMARYLLIDACEAE 

Agava ohrysoglosaa Jtn. z 

A. ohrysoglossa Jtn. ? z 

A. dentlens Trel. z 

A. subslmplez Trel. z z z z 

A. yaqulana Trel. z z 

Agave (Euagave) sp. z 

Agave (Llttaea) sp. z 

APOCYNACEAE 

Haplophyton olmloldum 

A. DC. z z 

Plumerla aoutlfolla 

Polr ? 

Vallesla balleyana 

Woodson * 

V. glabra (Cav.) Link z z z z 

ASCLEPIADACEAE 

Asoleplas albloans Wats. z z 

A. leptopus Jtn. z 

A. subulata Deo. z z z z 

Marsdenla edulls Wats. z z z 

Matelea oordlfolla (Gray) z 

Woodson 

M6


H* pringlel (Gray) 

Woodson x 

Metastelma pringlel Gray x 

M, watsonianua Standi* x 

Saroostemma olausum 

(Jaeq*) Soh. x 

S, heterophylla Engels x x 

unidentified vine x 

BATIDACEAE 

Batis maritima L. x x x x 

BORAGINACEAE 

Bourrerla sonorae Wats x 

Coldenia oanesoens DC x 

C« ouspldata Jtn* x 

C. palmeri Gray x x x 

Cordla brevlaploata x 

C. parvlfolia A. DC x x x x 

C. sonorae Rose x 

Cryptantha angelica Jtn. x 

C« angustlfolla (Torr.) 

Greene x x x x 

C. fastigiata Jtn* x x 

C. maritima Greene x x x x x 

Heliotropium ourassavicum 

L. xx xx 

Tournefortla hartweglana 

Steudel x 

BROMELIAGEAE 

Hechtia montana Brdge* x 

Tlllandsia exserta Fern. x 

T* reourvata L. x 

417

BUB3EBACEAE 


Bursera hindsiana (Benth.) 

Easier x x x x x x x x 

B. laxiflora Wats* x x 

B. miorophylla Gray xxx xxx xx 

B. odorata Brdge. xxx x 

BUXACEAE 

Simmondsla ohlnensls 

(Link.) Sohnled. xxx x x x x 

CACTACEAE 

Carneglea gigantea 

(Engelm.) Br. & B. x x x x x x 

Eohinooereus engelmatinli 

(Parry) Rumpler x x x 

E. grandis Br. & R. x 

E. 80opulorum Br. & B. x 

E. web8terlan.ua Lindsay E 

E. sp. E 

Ferooaotus covillei Br. 

& H. x x 

F. wislizenil (Engelm.) 

Br. & B. xx xx 

Lemaireooereus thurberl 

(Engelm.) Br. & B. xxxxxxx?xx 

Lophooereus sohottil 

(Engelm.) Br. & R. x x x x x x x 

Haohaerooereus gummosus 

(Engelm.) Br. & B. x x x x x 

Mammlllaria of. 

angelensis Craig x 

M. booensis Craig x 

M. booleyi Lindsay E 

H. of. dioioa Brdge. x x 

418


M. evennannlana 

(Br. & R.) Oroutt x 

M. inalae Craig x 

M. johnstonll (Br* & R.) 

Oroutt £ 

M. mlorooarpa Engelm. x x x x 

M. multidlgltata Lindsay E 

M. sheldoni (Br* & R.) 

Boed. x x 

M. swinglel (Br. & R.) 

Boed. x xx 

H. yaquensis Craig x 

M. oliTlae Oroutt ? x 

M. sp. x 

Opuntla bigelovii Engelm. x x x x x x 

0. of. bravoana Baxter x x 

0. fulglda Engelm. var. 

fulglda xx x x x x x 

0. fulglda Tar. 

maamillata (Sohott.) 

Coulter x x x x 

0. gossellnlana Weber x 

0. leptooaulls DC. x x x x x 

0. marenae Parson x x 

0. of. phaeaoantha 

Engelm. x 

0. versicolor Engelm. x x x x x 

0. (oylindropuntla) sp. x 

Faohyoereus pactinarborlginum 

(Engelm.) x 

Br. & R. 

P. pr ingle 1 (Wats.) xxxxxxxxxx 

Pereskiopsls porteri 

(Weber) Br. & R. z 

k!9


Peniooereus marianus 

(Gentry) Sanch. Me j or. x 

Rathbunia alamosensis 

(Coult.) Br. & R. x 

Wilooxia albiflora Baokeb. x 

W. striata (Brdge.) 

Br* & R. xxx xx 

CAMPANULACEAE 

Lobelia oardinalis subsp. 

graminea (Lam.) MoVaugh x 

Nemaoladus glanduliferus 

Tep. x 

CAPPARIDACEAE 

Atamiaquea emarginafca 

Miers, x x ? x x x x 

Cleome tenuis Vats. x x 

Porchammeria watsonii 

Hose z 

Wlsllzenia refraota var. 

palmeri (Gray) Jtn. x x 

W. refraota var. 

mammillata (Rose) Wigg. x x 

CARYOPHYLLACEAE 

Aohyronyohia oooperi Gray x x x ? 

Drymarla halosteoides 

Benth. x 

CELASTBACEAE 

Maytenus phyllanthoides 

Benth. x x x x 

CHENOPODXACEAE 

Allenrolfea occidentalis 

(Vats.) Kuntze x x xxx 

4-20

Atriplex barolayana 

(Benth.) Dietr. 

A* oanesoens (Pursh.) 

Nutt. 

A. linearis Wats* 

A. polyoarpa (Torr.) 

Wats. 

Chenopodlum nurale L. 

Salicornia paolfioa 

Standi* 

Suaeda torreyana rax* 

raaoalasina (Standi.) 

Munz. 

S. sp. 

COCHLOSPERMACEAE 

Aaoreuxla palnatlflda 

Sesse. & Moo. 

COMBRETACEAE 

Lagunoularia raoomosa 

(L.) Gaertn. 

COMMELINACEAE 

Coounelina sp. 

COMPOSITAE 

Baooharis glutinosa Pers. 

B. sarothrdLdes Gray 

Bebbia junoea (Benth.) 

Greene 

Brlokellla ooulteri 

Gray 

Coreooarpus arlzonlous 

(Gray) Blake 

C. 8hrevel Sherff. 


X X X X X X X X 

? XX 

XX XX 

X X X X X X 

XX X ? X 

XX XX 

X X X X X X 

X 

X X 

X ? XX 

X X 

X 

x X 

X X X X X 

X x 

X X X X X X 

X 

^21


C. sp* x 

Dioorea oanesoens Gray x 

Dyssodla oonolnna (Gray) 

Robinson x x 

Enoelia farlnosa Gray x x x x x 

E. hallmlfolia Cav. x 

Eupatoriua sagittatua 

Gray x x x 

Franserla aabrosioides 

Cav. x xx 

F* oamphorata var. 

leptophylla Gray x 

F. oordifolia Gray x 

P. deltoldea Torr* x ? x 

F. divarioata Brdge. x x x 

F. duaosa Gray x x x 

F* illolfolla Gray x x 

Haplopappus sonorlensis 

(Gray) Blake x x x 

H* of* tenulseotls 

(Greene) Blake x 

H. sp. x 

Helianthus niveua 

(Benth.) Brdge* x x x 

Hofmeisteria orasslfolia 

Vats. z x 

H* fasoioulata (Benth.) 

Walp. var* fasoioulata x x x x x 

H. laphaaioides Rose 

var* laphamioldes xxxxxxx x 

H* laphaaioides var* 

pauolseta (Jtn*) Blake s 

Hyaenoolea aonogyra 

Torr* & Gray x x 

Lagasoea deolpiens 

Hemsl* 

1 

1+22


Palafoxla linearis (Car.) 

Lag* rar. linearis x x x x x 

Peotis palneri Vats* x x 

P. papposa Haw* & Gray x x x 

Peluohia trifida Wats* x 

Perityle oalifomioa 


P. emoryl Torr* xxxxxxxxx 

P. palmsri Vats* x 

Peuoephyllum sohottil 

•ar* latisetium Jtn* x 

Porophyllum orasslfollum 

Vats* x x 

P* graeile Benth* x x x x x 

P* pausadynum Robins* & 

Green x x 

Stephanomeria pauoiflora 

(Torr*) Nels* x 

Trixis oalifomioa Kell* xxx x xxxx 

Verbesina sp. x x 

Viguiera deltoidea Gray xxx x x?xx 

CONVOLVUIACEAE 

Cressa truxillensis 

H.B.K* xx xxx 

Cusouta amerioana L* x 

C* leptantha Eng. x 

C* macrooephala 

Sohaffner * 

C* umbellata var. dubia 

Yunoker x 

C* spp* xx xx 

Brolvulus alsinoides var. 

aoapuloensis (Willd.) 

Ooststr* z x 

^23


Ipomoea arboresoens 

(Humb. Bonpl.) G. Don x 

I* sp. x x 

I. sp* x 

Jaoquemontla alblda Vigg. x x 

J* abutiloides var. eastwood 

iana (Jtn.) Vigg. x 

J. palneri Vats. x 

J. pringlel Gray ? x 

CRASSULACEAE 

Tillea ereota Hook. & Am. x 

CRUCIFEBAE 

Desouralnla plnnata subsp. 

halletorum (Cookerell) 

Detl. x x 

Lyrooarpa ooulterl Harv. 

var. ooulterl x x x x x 

L. linearifolla Roll. x 

Sisymbrium sp. ? 

unidentified (annual) x 

CUCUBBITACEAE 

Maximowiozla sonorae Vats. x x x 

Tunamooa maodougalil Bose x 

Vaseyanthus lnsularis Rose x x x x x 

CYPERACEAE 

Cyperus arlstatus Roth. x x x 

C. elegans L. x x x 

C. esculentus L. x x 

C. ferox Hioh. x 

Eleooharls genloulata (L.) x x 

42^


Fulrena simplex Vahl. x 

EUPHORBIACEAE 

Aoalypha californloa Benth. x x x x -x x 

A. oomonduana Mlllsp. x 

Adella obovata Wigg. & 

Roll. x 

Andraohne oiliatoglandulosa 

(Mlllsp,) 

Croizat x x 

Bernardla sp. x 

CnldosoolUB palmerl 

(Wats*) Rose x x 

Croton oallfornlous 

Muell. Arg. xx xx 

C« magdalenae Mlllsp. x x 

C. sonorae Torr. x x x x 

Ditaxis lanoeolata 

(Benth#) P. & H. xxx x x x 

D. neomexioana (Muell. 

Arg.) Heller xxx x x x 

Euphorbia albomarginata x 

E. arizonloa Engelm. x 

E. oalifomica Benth. x 

E. oapitellata Engelm. x 

E. oeroderma Jtn. x 

E. colletloldes Benth. x 

E. eriantha Benth. x x xxx 

E. incerta Brdge. x x 

E. leuoophylla Benth. x x 

E. magdalenae Benth. x 

E. mioromera Boiss. x 

E. misera Benth x x x 

E. pedioulifera Engelm. xxx x x x 

1*25


E. petrlna Vats* x ? x x x x x 

E. poly oar pa Benth. x x x x x x 

E. setlloba Engelm. x x x 

£• tomentulosa Wats. x x x 

E. xanti Engelm. x 

Jatropha oinerea 

(Ortega) Muell. Arg. x x x x 

J. ouneata Wigg & Roll x x x x x x x 

Maillot angustiloba (Torr.) 

Muell* Arg* x 

Fedllanthus naorooarpua 

Benth. x x 

Saplum biloculare (Wats.) 

Fax. xx x 

Tragla amblyodonta 

(Muell* Arg.) P. & H. xx x 

FOUQUIERIACEAE 

Fouqulerla maodougallil 

Nash x 

F. dlguetll (vail Tleghem) 

Jtn. x xx 

F. splendens Engelm. x x x x 

FRANKENIACEAE 

Frankenia palmer1 Wats. x x x 

GRAMINEAE 

Andropogon sp. x 

Aristida adsoenslonls L. xx x xxxx 

A. oallfomloa (Wats.) x x x x 

A. sp. X X X X X 


(H.B.K.) Grlseb. xxxxxxx xx 

B. barbata Lag. x x x x x x 

**26


B. sp. X 

Cathestloum erecturn 

Vasey & Hask x x 

Cenchrus palmerl Vasey x x x x x x x 

Chlorls brandegeei 

(Vasey) Swallen x 

C. vlrgata Swartz x x 

Cynodon daotylon (L.) 

Pers. x 

Daotylootenium aegyptlum 

(L.) Beauv. x 

Dlstlchlls spicata var. 

striota (Torr.) Beetle 

Eragrostls diffusa Buckl. x 

E. pllosa (L.) Beauv. x 

Heteropogon oontortus 

(L.) Beauv. x x x x x 

Hilarla belangerl var. 

longlfolia (Vasey) 

Hitoho. x x 

Jouvea pllosa (Presl.) 

Soribn. x 

Laslaous sorgholdes 

(Desn.) H. & C. x 

Leptoohloa unlnervla 

(Presl.) Hltcho. & Chase x 

L. sp. X X X 

Monanthoohloe littoralis 

Engelm. x x x x x 

Muhlenbergla mlorosperma 

(DC) Kunth x xx 

M. porterl Soribn. x 

Panicum arlzonloum 

Soribn. & Merr. ? x x x x ? x 

P. hlrtloaule Presl. x 

*f2?


P. sonorum Beal. 

P. stramineun Hitoho. 

& Chase x 

Phraguites oonnunis Trin. x x x 

Setaria grisebaohii 

Foum. x 

S. liebmannii Fourn. x x x 

S. palmerl Henrard x x x 

Sporobolus oryptandrus 

(Torr.) Gray 

S. patens Swallen 

S. virglnious (L.) Kunth. x x x x x 

Triohaohne oalifornioa 

(Benth.) Chase x x x 

Tridens pulohellus 

(H.B.K.) Hitoho. x 

HYDROPHYLLACEAE 

Nana hispidum Gray x x 

Fhaoelia mlnutlflora 

Munz xx x 

KOEBERLINIACEAE 

Koeberlinia spinoaa var. 

tenulspina Kearn. & Peeb. x x x 

LABIATAE 

Hyptis emorylTorr. x x x x x x 

Salvia similis Brdge. x 

Teuorium oubense subsp. 

depressum (Small) 

MoClint. & Epl. * 

LEGUMIN03AE 

Aoaoia oalifornioa 

Brdge• 

x 

kZQ


A. oonstrlota Benth# 

A. oymbispina Sprague 

& Riley x 

A. farneslana (L.) 

Wlllo. x 

A. greggll Gray x x x x 

A. wlllardlana Rose x x x x 

Astragalus magdalenae 

Greene x 

Nuttallianus DC* x x 

Benthamantha edwardsll 

(Gray) Rose x 

Caesalpinia palmer1 

Wats. x x 

C. pumila (Br. & R.) 

Hermann x 

Calliandra californioa 

Benth. x 

C. erlophylla Benth. ? x x 

C. rosel Vlgg. x x 

Cassia oonflnis Greene x 

C. covesll Gray x x x x x 

Ceroldlum florldum 


C. mlorophyllum (Torr.) 

Rose & Jtn. xx x x x 

C. praeoox (Ruiz & 

Pav.) Harms. x 

Coursetla glandulosa 

Gray x x 

Dalea emoryl Gray x x x x 

D. mollis Benth. 

neomexlcana (Gray 

Cory-oomplex x x x x x 

D. parryl Torr. & Gray x x x x x x 

J^29


Desmanthus covlllel 

(Br. & R.) Wigg. ex 

Turner x 

D. frutloosus Rose x x x x 

D. palmerl (Br. & R.) 

Wigg. ex Turner x 

Diphysa oooidentalls Rose ? x 

Erythrina flabelllformis x 

Kearney 

Errazurizla megaoarpa 

(Wats.) Jtn. x x 

Raematoxylon braseletto 

Karst• x 

Hoffmanseggia intrioata 

Brdge. x x x x x 

Indlgofera laevls Rydb. x 

Kramerla grayl Rose & 

Painter x x x x 

K. parvlfolia Benth. x x ? x 

K. sonorae Brit. x x 

Lotus salanglnosus yar. 

brevevexlllus Ottley x 

L. tomentellus Greene x x 

Luplnus arlzonlous Vats. x x x 

Lyslloma oandlda Brdge. x 

L. dlvarioata (Jaoq.) 

Macbr. x x 

Mimosa laxlflora Benth. x x x 

Nlssolla sohottll 

(Torr.) Gray x 

Olneya tesota Gray xxxxxxx x 

Phaseolus flllformis 

Benth. x x x x x x 

Fitheoolobium oonfine 

Standi. xxx 

4-30


P. sonorae Wats. x 

Prosopis artioulata Wats* x 

P. Jullflora DC. x 

P. torreyana x x x x x x x 

Sphlnotospermum oonatrioturn 

(Wats.) Hose x 

Tephrosla palmeri Wats. x x x 

LOASACEAE 

Euonide oordata Kell. x x 

Mentzella adhaerans Benth. x x x x x x x 

H. hlrsutisslma Wats., x 

Petalonyx linearis Greene x x x 

Sympeteleia rupestrls 

(Balll.) Gray x x x x x x x 

LORANTHACEAE 

Phoradendron callfornlcum 

Nutt. xx xx 

P. diguetlanum Van 

Tieghem x x x x 

Phrygllanthus sonorae 

Wats. x 

Struthanthus haenkeanus 

(Presl.) Standi. x x 

MALPHIGIACEAE 

Eohinopterys eglandulosa 

(Juss.) Small x 

Janusia oalifornioa 

Benth. xxx x 

J. gracilis Gray xxx x x x 

Masoagnla maoroptera 

(Sesse & Moo.) Ndzu. x x x 

Thryallls augustifolia 

(Benth.) Kuntze x x x 

*4-31

MALVACEAE 


Abutilon oalifomioum 


A, or 1 spurn (L.) Sweet x x x x 

A. inoanum (Link) Sweet x x x x 

A. palmeri Gray x x x 

Gossypium klotzohianum 

subsp* davidsonll (Kell.) 

Hutoh* x x 

Hibisous biseptus Wats* x x 

H. denudatus Benth. x x x x x x 

Horafordia alata (Wats*) 

Gray x x x x 

H. newberryi (Wats*) 

Gray x x x x 

Sida hederaoea Torr. 

ex Gray x 

Sphaeraloea ooulteri 

(Wats*) Gray x x x 

S. hainesii Brdge. x 

S. orouttii Hose x x 

3* spp* xx xx 

MARTYNIACEAE 

Probosoidea altheaefolia 

(Benth.) Deone* x x x 

MENISPERMACEAE 

Coooulus diversifolius 

DC. X x 

MORACEAE 

Fious pad!folia H.B.K. 

F* palmeri Wats. xxxxx xxxx 

F* petiolaris ii.B.K. x 

**32


F. radullna Wats. x 

NYCTAGINACEAE 

Abronla maritlma Nutt. x x x x x 

Abronia sp* x 

Alllonla lnoarnata L. x x x x x 

Boerhaavla ooulteri 

(Hook, f.) Wats. xx x 

B. ereota L. x x x x x x 

B, xanti Wats* x 

B. sp. X 

Commloarpus soandens 

(L.) Standi* x x x 

Ptsonia capltata (Wats*) 

Standi. x 

OLACACEAE 

Schoepfla shreveana Vlgg. x 

ONAGRACEAE 

Camlssonla eardlophylla 

(Torr.) Haven x x x 

C. ohamaenerloides (Gray) x 

Jussiaea suffrutloosa L. 

ootofolla (DC.) Munz z 

Oenothera oallfornloa 

subsp. arizonloa {Munz) 

Klein x 

0. leptooarpa Greene x x 

PALMAE 

Erythea olara Bailey x 

Sabal uresana Trel* z 

Washlngtonla robusta 

Wendl. x 

433

PAPAVERACEAE 

Argemone subintegrifolia 

0>raby 

A. sp. 

PA3SIPL0BACEAE 


Passiflora arida (Mast. & 

Rose) Killip* var. arida x z z z 

P. foetida var, gossyplfolla 

(Desv.) Mast* i z 

P. mezioana Juss. z 

PHYTOLACCACEAE 

Phaulothamnus spinesoens 

Gray z z z z z z z 

Stegnosperma hallmifollum 

Benth. 

PLUMBAGINACEAE 

Plumbago soandens L. x z 

POLYGONACEAE 

Antlgonon leptopus H. & A* x 

Coocoloba goldmannii 

Standi. x 

Eriogonum inflatum 

Torr. & Frem. z z 

PTERIDACEAE 

Notholaena oalifomioa 

Eaton x x 

N. sp. x 

Chellanthes sp. x 

x 

z

PORTULACACEAE 


Portulaoa lanoeolata 

Engelm. x x 

P. parvula Gray x 

P. suffrutesoens Engelm. x 

P. sp. x 

BESEDACEAE 

Oligomerla linlfolia 

(Vahl.) Maobr. x x 

RHAMNACEAE 

Colubrlna glabra Wats xxxxx x xx 

Condalla globoaa Jtn. 

var. pubeaoens Jtn. x x x x x x 

C. lyoloides var. 

canesoens (Gray) Trel. x x x x x x 

Gouanla rosei Wigg. x 

Zizyphus sonorensls « 

Wats. x 

RHIZOPHORACEAE 

Rhlzophora mangle L. 

RUBIACEAE 

Hlntonla latiflora 

(Sesse & Moo.) Bull. 

Bandia thurberl Vats. x x 

R. sp. x 

RUTACEAE 

Zanthoxylum arboresoens 

Rose x 

Z. sonorense Lundell x 

435

SALICACEAE 

Saliz goodding11 Ball 

SAPINDACEAE 

Cardiospenmun oorIndian L. 

Dodonaea vlsoosa (L.) 

Jaoq* 

Saplndus saponarla L. 

SAPOTACEAE 

Brunei la oooIdentails 

Hemsl• 

Slderoxylon leuoophyllum 

Wats* 

SCROPHULABIACEAE 

Antirrhinum oostatum Wlgg. 

A* oyathlferum Benth• 

A. kingi var. watson11 

(Vasey & Rose) Hunz 

Galvezla Juncea var« 

pubesoens (Brdge.) Jtn. 

Llnaria oanadensla Var* 

texana (Soheele) Pennell 

Stemodla durantlfolia (L.) 

Swartz 

3IMARUBACEAE 

Castela sp. 

SOIANACEAE 

Datura dlsoolor Benth. 

Lyolum spp. 

Nlootiana Cleveland11 

Gray 


z 

X X X X X 

X X 

X X ? X 

X 

X 

X X X X X X X X 

X 

X 

X 

X 

X x 

X X x x x 

x x x x x x x x x x 

X X 

**36


N. trlgonophylla Ounal. xxxxxxxxx 

Physalis orassifolia var, 

infundibularis Jtn. x 

P. purpurea Wigg. x 

P. spp. xx xx 

Solanum hindsianum 

Benth. x x x x x x 

STERCULIACEAE 

Ayenia oompaota Rose x x x x 

A. glabra Wats* x x 

A. pusilla L. x 

Hermania pauoiflora Vats. x 

Me lochia tomentosa L. x x x x 

TAMARICACEAE 

Tamarix aphylla (L.) 

Karat• x 

T. pentandra Fall. x x 

THEOPHRASTACEAE 

Jaoquinia pungens Gray x x x 

TYPHACEAE 

Typha domingensis Pers. x 

ULMACEAE 

Celtis pallida Torr. x x x x 

C. reticulata Torr. x 

UMBELLIFERAE 

Erynginum nasturtilfollum 

Juss. * 

^37

UHTICACEAE 


Parietarla florldana 

Nutt. x x 

VERBENACEAE 

Avioennla gormliians 

(L.) L, xx xx 

Bouohea disseota Wat, x 

Citharexylum flabellifolium 

Wats. x 

Lantana horrida H.B.K. x x 

Llppla palmeri Wats* x x x x x 

Verbena menthifolia 

Benth. x 

VIOLACEAE 

Hybanthus frutioulosus 

Tar. flavesoens (Dowell) 

Jtn. x x 

2YG0PHYLLACEAE 

Fagonla oalifomica 

Benth. x x x x x 

F. paohyaeantha Rydb. x 

F. palmeri Vasey & Rose x 

Guaiaoum ooulteri Gray x x 

Kallstroemla oalifomica 

(Wats.) Vail xxx x x 

X. grandiflora Torr. x x x x 

Larrea divaricata Cav. x x x x 

Trlbulus terrestris L. x x x 

Visoainoa genloulata 

(Kell.) Greene var. 

genloulata xxxxxxxxx 

^38

APPENDIX B

APPENDIX B 

DISTRIBUTION LIST OF AMPHIBIAN AND BEFTILE SPECIES FOR 

ISLANDS AND REGIONS IN THE GULF COAST OF SONORA 

I, INFERNILLOl T, ISLA TIBURON; D, ISLA DATIL; Ct ISLA CHOL- 

LUDOj E, ISLA SAN ESTEBAN; A, ISLA. ALCATRAZ{ L,"~LLANURAS| M, 

ISLA SAN PEDRO MARTIR; G, GIJAYMAS; N, ISLA SAH PEDRO NOLASCO 

Amphibians: 


Bufo alvarlus Girard x ? x 

B. punotatus Baird & 

Girard ? x ? x 

Hyla arenlcolor Cope x 

Soaphiopus oouohl 

Baird x x x ? 

Rana plplens 

Sohreber x 

Reptllosj 

Gophorus agassizl 

Cooper xxx x x 

Chilomenlsous olnotus 

Cope x x 

Chlonaotis ocolpltalls 

Hallowell x 

C. palarostrls Klauber x 

Constriotor oonstrlotor 

lmperator (Daudln) x 

Crotalus atrox Baird 

& Girard x x xxx 

C* molossus molossus 

Baird & Girard x x 

C. molossus estebanensls 

Klauber x x 

C. oerastes oeroobombus 

Savage & Cliff x x x x 

C. tlgrls Kennloott x


Elaphe ohlorosoma 

(Gunther) x 

Fiolmla desertorum 

Taylor x 

Hypslglena torquata 

oohrorhynoha Cope x x 

H. torquata venusta 

Mooquard x 

Lampropeltls getulua 

nigritls Zweifel & Norris x 

Liohanura trlvirgata Cope x x 

Mastioophis bllineatus 

Jan sap* ? x 

M. bllineatus slevini 

Lowe & Norris 

xx 

flagellum olngulum 

Lowe & WoodIn x x 

M. flagellum pioeus 

Cope 

M. flagellum Shaw? 

z x 

Mlcruroldes euryxanthus 

euryxanthus (Kennloot) x x 

Oxybelis aeneua auratus 

(Bell) x 

Phyllorhynohus browni 

Stejneger 

P. deourtatus nubills 

x 

Klauber 

x 

Pltuophls melanoleuous 

affinis Hallowell x x x x 

Rheinooheilus leoontel 

antonl Klauber x 

Salvadora hexalepls 

hexalepis Cope x x 

S. hexalepis 

desertloola Sohmldt x x 

1


Tantllla hobartsmlthl 

Taylor E 

Thamnophls cyrtopsls 

Kennloott x 

Trlmorphodon lambda 

lambda Cope x x 

Calllsaurus draoonoldes 

Inusltatus Diokerson x x x x 

Cnemldophorus bacatus 

Van Denburgh & Slevln £ 

C. burtl Taylor x 

C. tlgrls aethlops Cope x x ? x 

C. tlgrls estevanensls 

Dickerson E 

C. tlgrls martyrls 

Stejneger E 

Coleonyx varlegatus 

sonorlensls Klauber x x ? x 

Crotophytus dlokersonae 

Schmidt x x 

Ctenosaura hemllopha 

hemllopha (Cope) ? ? x x 

C. hemllopha 

oonsplouosa Diokerson ? ? x x 

Dlpsosaurus dorsails 

sonorlensls Allen x ? x x 

Gambella wisllzenl 

wlsllzenl (Balrd & 

Glrard ? x ? x 

Gerrhonotus klngl 

nobllls Balrd & 

Glrard x 

Heloderma suspeotum 

suspeotum Cope x x x 

Holbrookla maoulata 

thermophlla Barbour ? x 

Phyllodaotylus homolepldurus 

homolepldurus 

Smith x 

W2


P# homolopldurua 

nolasoensls Dixon £ 

P. xantl Cope x ? x x x 

Phrynosoma platyrhinos 

goodel Stejneger x 

P. aolare Gray ? x x x 

Sauromalus obesus 

towsendl Dickerson x x x x x 

S. varlus Dlokerson E 

Soeloporus olarkl 

olarkl Balrd & Glrard x 

3. maglster maglster 

Hallowell x x x x 

Urosaurus ornatus 

lateralis Boutenger x ? x 

Uta palmer! Stejneger E 

U. nolasoensls Van 

Denburgh & Slevln B 

U. stansburlana 

klauberl Lowe & Norrls £ 

IT. stansburlana 

stejnegerl Schmidt* x x x x x x 

U. stansburlana 

taylorl Smith £ 

Xantusla vlgllls Balrd x

APPENDIX C

APPENDIX C 

DISTRIBUTION LIST OP MAMMAL SPECIES, EXCLUSIVE OP BATS AND 

MARINE SPECIES FOR ISLANDS AND REGIONS IN THE GULP COAST OF 

SONORA 

I, INFERNILLO; T, ISLA TIBURON{ D, ISLA DATIL; L, LLANURAS; 

~ G, GUAYMAS; N, ISLA SAN PEDRO NOLASCO " 

Antelooapra amerloana 

mezleana Merrlam 

Cauls latrails neamsi 

Merrlam 

C. latrans jamesl 

Tovnsend 

Cltellus teretioaudus 

negleotus (Merrlam) 

Dipodomys desert1 

sonoriensls Goldman 

D. merriami merriami 

Mearns 

D. merriami mltohelll 

Mearns 

Eutamlas dorsails 

dorsalis (Baird) 

Fells oonoolor azteca 

Merrlam 

Lepus alleni alleni 

Mearns 

L* alleni tiburonensis 

Towsend 

L. californious 

eramicus Allen 

Lynx rufus balleyi 

Merrlam 

Mus musoulus muscuius 

L. 

Neotoma albigula 

melanura Merrlam 

I T D E L G N 

——— m i i 

? 

z 

z 

z 

? 

E 

E 

z z 

? z 

z 

? z 

z 

? X 

z z 

? 

? 

z z 

x 

4^5

I T D E L G N 

N. alblgula aeri 

Townsend E 

N. alblgula venusta 

True ? ? 

N. varla Burt E 

Odoooileua oouesi 

(Coues & Yarrow) z ? ? 

0. hemlonis eremious 

{Mearns) x x ? ? 

Onyohomys torrldus 

torrldus (Coues) x 

Oryzomys oouesi Iambi 

Burt x 

Ovis oanadensls 

galllardl Mearns x 

Pecarl angulatus 

sonorlensis (Mearns) x x x 

Perognathus balleyl 

balleyi Herrlam x 

P. balleyi insularIs 

Townsend E 

P. flavus sonorensls 

Nelson .& Goldman ? 

P. lntermedlus lithophllus 

Huey ? 

P. longlmembrls 

kinoensls Huey x 

P. penicillatus minimus 

Burt E 

P. penicillatus price1 

Allen ? ? x 

P. penicillatus seri 

Nelson E 

Peromysous boyli 

glasselll Burt E 

P« oollatus Burt E 

\ 

446

I T D E L G N 

P. oremlous anthonl 

(Merrlam) x 

P. eramicus eremlous 

(Baird) x ? 

P. eremlous tiburonensis 

Mearns ? x 

P. pembertoni Burt E 

P. stephani Townsend E 

Prooyon lotor pallldus 

Merrlam x x x 

Rattus rattus alexandrlnus 

(Geoffrey) x x x 

Re1throdontomya megalot1s 

megalotIs (Baird) x x x 

Slgmodon hispidus major 

Bailey x 

Sylvllagus audubonl 

arizona© (Allen) x x 

S. audubonl goldmanl 

(Nelson) z 

Taxidea taxus berlandieri 

Baird x x x 

Teanopus phenox Merrlam x 

Thomomys bottae oonvergens 

Nelson & Goldman ? ? 

4^7

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1

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