STUDIES IN MYCOLOGY 53: 83–120. 2005.
Oidiodendron: A survey of the named species and related anamorphs of
Myxotrichum
Adrianne V. Rice* and Randolph S. Currah
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9 Canada**
*Correspondence: Arice@NRCan.gc.ca
Abstract: Synoptic and dichotomous keys to 23 species of Oidiodendron and similar arthroconidial anamorphs of Myxotrichum
were developed using morphological and physiological characters. Illustrations and brief descriptions based on living isolates
and published descriptions are provided for all species treated. Included are the unnamed Oidiodendron states of Myxotrichum
arcticum, M. cancellatum, M. emodense, M. setosum, and M. striatosporum, as well as the anamorphic species O. ambiguum, O.
cerealis, O. chlamydosporicum (inclusive of O. scytaloides as a synonym), O. echinulatum, O. fimicola, O. flavum, O. fuscum,
O. griseum, O. hughesii (inclusive of O. reticulatum as a synonym), O. maius (inclusive of O. maius var. citrinum and O. maius
var. maius), O. muniellense, O. myxotrichoides, O. periconioides, O. pilicola, O. rhodogenum, O. setiferum (inclusive of O.
ramosum as a synonym), O. tenuissimum, and O. truncatum. Oidiodendron fuscum, the original type species, is recognized as
distinct. Oidiodendron robustum is excluded because of its large conidia and conidiophores and because the original drawings
do not convincingly portray arthroconidia. Oidiodendron terrestre is excluded because its large, two-celled conidia, rapid
growth, and hyaline conidiophores are inconsistent with the generic diagnosis and because the mode of its conidiogenesis is
unclear from the original descriptions and illustrations.
Taxonomic novelties: Oidiodendron maius var. citrinum (Barron) Rice & Currah stat. nov.
Key words: dichotomous key, Myxotrichum, morphological characters, Oidiodendron, Oidiodendron fuscum, Oidiodendron
maius var. citrinum, Oidiodendron maius var. maius, physiological characters, synoptic key.
INTRODUCTION
Species of Oidiodendron Robak and the anamorphs of
Myxotrichum arcticum Udagawa, Uchiyama & Kamiya,
M. cancellatum Phillips, M. emodense Udagawa &
Uchiyama, M. setosum (Eidam) Orr & Plunkett, and
M. striatosporum (Barron & Booth) Sigler produce
distinctive chains of small (< 6 µm long), unicellular
arthroconidia through the basipetal fragmentation of
hyaline fertile hyphae. The fertile hyphae arise from the
apices of solitary, erect, smooth to asperulate, melanized
conidiophores that are normally 5–500 µm long,
though some species diverge significantly from this
pattern. Oidiodendron myxotrichoides Calduch, Gené
& Guarro produces fertile hyphae from the melanized
branches of a reticulate conidioma. Oidiodendron
hughesii Udagawa & Uchiyama, O. muniellense
Calduch, Stchigel, Gené & Guarro, and O. setiferum
Udagawa & Toyazaki have branched, melanized
appendages surrounding the conidial mass at the
conidiophore apices. Oidiodendron cerealis (Thüm.)
Barron and M. setosum have short, hyaline to lightly
melanized conidiophores and O. chlamydosporicum
Morrall has thick-walled, melanized chlamydospores.
**Current address for Adrianne V. Rice; Northern Forestry
Centre, Natural Resources Canada, 5320-122 St., Edmonton,
AB T6H 3S5 Canada
The anamorph of M. arcticum also produces whorls of
conidia that occur singly and in truncated chains along
the conidiophore apex.
Conidia are hyaline to dark and are lens-shaped,
globose, subglobose, ellipsoidal, cylindrical, barrelshaped, pyriform, or irregular. Surface texture is
asperulate, verruculose, dimpled, rugose, spinulose,
or reticulate. Scanning electron microscopy (SEM)
shows that the characteristic surface ornamentation is
due to the presence of a persistent perispore membrane
derived from the wall of the conidiogenous hypha. Wall
material from the conidiogenous hypha also persists
between adjacent conidia where it eventually collapses
to form “connectives”.
Species of Oidiodendron have been isolated
worldwide, mostly from soil and decaying plant
materials (Peyronel 1914, Smith 1946, Malan 1949,
Barron 1962, Morrall 1968, Kobayasi 1969, Ellis 1971,
Udagawa & Toyazaki 1987, Hambleton et al. 1998,
Sigler & Flis 1998, Hambleton et al. 1998, Calduch et
al. 2004, Roose-Amsaleg et al. 2004).
Despite the widespread occurrence of this genus,
there is no comprehensive key to the species. The
keys in Barron (1962), Ellis (1971, 1976), Domsch et
al. (1980), and Calduch et al. (2004) are out of date
and rely exclusively on morphological characters.
Calduch et al. (2004) include 23 species but four are
not well accommodated in Oidiodendron, and three are
83
RICE & CURRAH
synonyms of other species. The unnamed anamorphs
of Myxotrichum species are not included in previous
keys.
Because morphological characters alone may be
inadequate in hyphomycete species identification,
as is often revealed by molecular studies, we sought
additional phenotypic characters by investigating a
suite of simple physiological tests. These have been
incorporated into updated dichotomous and synoptic
keys to 24 species or varieties. Preceding the keys is
a review of the taxonomic history, distribution and
ecology of the genus. Following a description of
the procedures used to describe morphological and
physiological characters is an assessment of their
taxonomic value. Species descriptions follow the keys
and are in alphabetical order.
Taxonomic History
The hyphomycete genus Oidiodendron was established
by Robak (1932) for three species isolated from wood
pulp, O. fuscum Robak, O. nigrum Robak, and O.
rhodogenum Robak. The genus has since grown to
encompass 18 species named in Oidiodendron and the
unnamed anamorphs of five species of Myxotrichum
Kunze.
Four species were added to the genus over the next
30 years. Newly described species included O. griseum
Robak from wood pulp (Melin & Nannfeldt 1934)
and O. flavum von Szilvinyi from soil (von Szilvinyi
1941). Species transferred into the genus included
Dicyma ambigua Peyronel, the putative anamorph
of Myxotrichum aeruginosum Mont. (Peyronel 1914,
Malan 1949), as O. ambiguum (Peyronel) Malan
(Malan 1949) and Periconia tenuissima (Peck) as O.
tenuissimum (Peck) Hughes (Hughes 1958).
In 1962, Barron reviewed the genus, adding four new
species, transferring a fifth, and designating two pairs
of synonyms. The new species Oidiodendron citrinum
Barron, O. echinulatum Barron, O. maius Barron, and
O. truncatum Barron were all isolated from peat soils in
Ontario. Trichosporium cerealis Thüm. was transferred
into Oidiodendron as an earlier synonym of O. nigrum
Robak. Barron also considered O. fuscum synonymous
with O. tenuissimum and designated it as the type of
the genus. The first key to the genus appeared in this
publication and included nine species, O. cerealis,
O. citrinum, O. echinulatum, O. flavum, O. griseum,
O. maius, O. rhodogenum, O. tenuissimum, and O.
truncatum (Barron 1962). Hambleton et al. (1998),
using ribosomal DNA sequences, determined that O.
tenuissimum sensu Barron comprised two species. Our
morphological and physiological evidence indicate
that these correspond with O. fuscum Robak and O.
tenuissimum (Peck) Hughes. We therefore recommend
reinstatement of the original type.
84
Between 1962 and 1968, three additional species
were described. The first of these was O. gracile
Zhdanova from the rhizosphere of maize (Zhdanova
1963). Morrall (1968) declared O. gracile a nomen
dubium because no type was designated and because
the original description and figures failed to clarify
whether the conidia were arthroconidial or were
produced by acrogenous budding. Morrall (1968) also
described O. chlamydosporicum and O. periconioides
Morrall from boreal forest soils.
In 1968, Tewari and MacPherson (1968) discovered
a fungus appearing to cause neuropathology in mice in
vitro. They later described this species as Oidiodendron
kalrae Tewari & MacPherson (Tewari & MacPherson
1971) [as “kalrai”]. This species was ultimately
transferred to Arthrographis as Arthrographis kalrae
(Tewari & MacPherson) Sigler & Carmichael [as
“kalrai”] on the basis of its hyaline conidiophores
and smooth conidia, which lack connectives (Sigler &
Carmichael 1976). Two new species were described
in 1969, Oidiodendron pilicola Kobayasi, based on
an isolate colonizing human hair in contact with soil
(Kobayasi 1969), and O. terrestre Roy & Singh from
Indian soil (Roy & Singh 1969). We exclude O. terrestre
from Oidiodendron because of its rapid growth, large,
two-celled conidia, and hyaline conidiophores, and
because the mode of its conidiogenesis is unclear in
the original descriptions and illustrations.
Stalpers (1974) transferred Oedocephalum
sulphureum Cooke & Massee into Oidiodendron as
O. sulphureum (Cooke & Massee) Stalpers but was
concerned that the species might be a synonym of O.
flavum. We have not examined the type, no cultures
are available, and Stalpers’ brief descriptions and
illustrations leave room for doubt. Further details
are found under “notes” following the description
of O. flavum. Tokumasu (1973) and Söderström
and Bååth (1978) isolated a species similar to O.
chlamydosporicum from soil in Japan and Europe;
it appeared as O. scytaloides in the key by Domsch
et al. (1980) although it was not validly published as
O. scytaloides Gams & Söderström until three years
later (Gams & Söderström 1983). Molecular evidence
(Hambleton et al. 1998, Calduch et al. 2004) and our
examination of ex-type cultures of O. scytaloides and
O. chlamydosporicum suggest that they are synonyms.
Cultures of “O. sindenia Beyer” were deposited in
the American Type Culture Collection (1976) but
the name was never validly published (Beyer, pers.
comm., 2002).
Two more species were described during the
1980s. The first, O. robustum Mercado Sierra &
Castañeda Ruiz, from bark of Bauhinia cumanensis
Kunth in Cuba (Mercado Sierra & Castañeda Ruiz
1985), is excluded based on its inordinately large
conidia and conidiophores and because the mode of
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
its conidiogenesis is unclear in the description and
illustrations. Oidiodendron setiferum was described
with branched, melanized appendages at the
conidiophore apex, and the generic description was
emended to accommodate this character (Udagawa &
Toyazaki 1987).
From this point on, a succession of new species
bearing such spiny or myxotrichoid appendages
was described. A second species with melanized
appendages that were more elaborate than those of O.
setiferum and that formed a “reticuloperidium-like”
structure surrounding the arthroconidia was named
O. hughesii in 1998 (Udagawa & Uchiyama 1998).
Calduch et al. (2002) described O. myxotrichoides,
which produces arthroconidia on the melanized hyphae
of a reticulate conidioma that superficially resembles
the “reticuloperidium” of Myxotrichum ascomata.
Calduch et al. (2004) described three more species
with melanized appendages: O. muniellense Calduch,
Stchigel, Gené & Guarro with setiform appendages
and subglobose, roughened conidia, O. ramosum
Calduch, Stchigel, Gené & Guarro with recurved
appendages and smooth to slightly roughened conidia,
and O. reticulatum Calduch, Stchigel, Gené & Guarro
with ellipsoidal, roughened conidia and appendages
resembling those of O. hughesii. Comparisons of the
original descriptions and illustrations of O. hughesii, O.
muniellense, O. ramosum, O. reticulatum, and ex-type
material of O. setiferum suggest that O. reticulatum is a
synonym of O. hughesii and O. ramosum is a synonym
of O. setiferum.
Finally, Rice and Currah (2005–this volume)
describe O. fimicola Rice & Currah from mushroom
compost. The description is based on two cultures
obtained from the Pennsylvania State University
Mushroom Spawn Laboratory.
In addition to the binomials in Oidiodendron,
listed above, one named species and five unnamed
species constitute the anamorphic components of
holomorphs named in Myxotrichum. Oidiodendron
ambiguum (Peyronel 1914, Malan 1949) is listed
as the anamorph of Myxotrichum aeruginosum and
unnamed Oidiodendron anamorphs are connected
with M. cancellatum (Orr & Kuehn 1964), M. setosum
(Orr et al. 1963), M. striatosporum [≡ Byssoascus
striatisporus (Barron & Booth) von Arx] (Barron &
Booth 1966, Sigler & Carmichael 1976), M. arcticum
(Udagawa et al. 1994), and M. emodense (Udagawa &
Uchiyama 1999). A relationship between the species
of Oidiodendron and teleomorphic taxa within the
Myxotrichaceae is strongly supported by molecular
evidence (Hambleton et al. 1998) in addition to these
anamorph-teleomorph connections. Placement of the
Myxotrichaceae among the inoperculate discomycetes
(Leotiomycetes) is supported by molecular data
(Sugiyama et al. 1999, Mori et al. 2000, Gibas et
al. 2002) and by a study indicating that the type of
ascocarp development occurring in Myxotrichum is
discomycetous in nature (Tsuneda & Currah 2004).
Distribution, occurrence, and ecology
Species of Oidiodendron are known as saprobes
and come from a variety of living and decomposing
plant, animal, and fungal substrates, including peat,
soil, humus, wood, lichens, marine sediments and
holothurians, human skin (incidental contamination
only) and decomposing human hair (e.g. Robak 1932,
Smith 1946, Barron 1962, Morrall 1968, Kobayasi
1969, Domsch et al. 1980, Hambleton et al. 1998,
Sigler & Flis 1998, Pivkin 2000, Lumley et al. 2001,
Calduch et al. 2004). They have also been identified
from human food supplies (Delamarre & Batt 1999,
Krysińska-Traczyk et al. 2001) and indoor air and
dust samples (Udagawa & Toyazaki 1987, Horak et al.
1996, Reiman & Uitti 2000). They occur throughout
the temperate regions (e.g. Domsch et al. 1980,
Hambleton et al. 1998, Sigler & Flis 1998) and there
are scattered reports from tropical and subtropical
locales (Ellis 1971, Hambleton et al. 1998, Sigler &
Flis 1998, Calduch et al. 2004, Roose-Amsaleg et al.
2004).
Oidiodendron maius var. maius appears to form
ericoid mycorrhizas in nature with members of
the Ericaceae (Couture et al. 1983, Douglas et al.
1989, Hambleton & Currah 1997, Johansson 2001,
Lacourt et al. 2001) and other species can produce
morphologically similar structures in vitro (Dalpé
1986, 1989, 1991, Currah et al. 1993). This relationship
is facultative for the fungi because they also persist as
free-living saprobes in the same habitat (Tsuneda et
al. 2001, Piercey et al. 2002, Rice & Currah 2002, in
press).
Despite the reports of Oidiodendron species from
a diverse array of substrates and environments, little
is known about their ecological roles in nature. Most
reports are incidental and indirect (e.g. Delamarre &
Batt 1999, Pivkin 2000, Lumley et al. 2001, RooseAmsalag et al. 2004). Few researchers try to isolate
Oidiodendron species specifically, and few speculate
on their ecological roles (Rice & Currah 2002). The
exception is O. maius var. maius, which is conceived
as having a mutualistic relationship with ericaceous
roots and can predictably be isolated from them
(Rice & Currah, in press). Most recent research on
Oidiodendron has focused on the mycorrhizal status
of various species and on the ecological significance
of this association (e.g. Couture et al. 1983, Dalpé
1986, 1989, Douglas et al. 1989, Dalpé 1991, Currah
et al. 1993, Perotto et al. 1995, Bending & Read 1997,
Hambleton & Currah 1997, Currah et al. 1999, Xiao
& Berch 1999, Piercey et al. 2002, Usuki et al. 2003).
85
RICE & CURRAH
While benefits to the host plants have been observed in
resynthesis studies, potential benefits to the mycobiont
(O. maius var. maius) have not been investigated.
Ecological assessments have been hampered by the
inability to identify species accurately (Hambleton
& Currah 1997, Hambleton et al. 1998, Lacourt et al.
2001). Misidentification of ericoid mycorrhizal isolates
has led to difficulty in interpreting the specificity
of these associations (Hambleton & Currah 1997,
Hambleton et al. 1998, Lacourt et al. 2001, Rice &
Currah, in press).
Targeted isolation studies are required to determine
which habitats and substrates are occupied by
Oidiodendron species. These studies must be based on
precise identifications so that estimations of the range,
abundance, and distribution of Oidiodendron species
in nature can be determined. Functional assessments,
including enzyme assays and physiological profiles,
mycorrhizal resynthesis and decomposition studies,
and tests for pathogenicity are required to elucidate the
niches occupied by these fungi. Data from functional
assessments and from distributional studies should
be compiled to provide a more accurate ecological
picture.
In vitro studies on the physiology of Oidiodendron
species can provide insight into the potential roles
these species play, although such studies do not
provide information about actual ecological niches.
Enzymatic studies on Oidiodendron have so far
concentrated on the ecological implications of the
cellulolytic abilities that have been detected (Dalpé
1991). All but two of the Oidiodendron species
tested degraded cellulose azure, and various species
produced other enzymes, including pectinases, lipases,
gelatinases, and polyphenol oxidases, that potentially
allow them to degrade a variety of plant, fungal, and
animal-based substrates, including those found in
soils. Broader substrate utilization profiles, including
those generated by BIOLOG analyses (Rice & Currah
2005–this volume) could provide more information
about the nutrition and potential ecological roles of
Oidiodendron spp.
Three Oidiodendron and two related Myxotrichum
species (M. cancellatum, M. setosum, O. hughesii, O.
myxotrichoides, and O. truncatum) are psychrophilic,
with temperature optima below 20 °C. The remaining
species are psychrotolerant, with temperature
optima of 20–25 °C but with the ability to grow at
temperatures as low as 5 °C. These species show
decreased growth at temperatures over 25 °C. Such
observations may explain the prevalence Oidiodendron
species in temperate climates, where average summer
temperatures are below 25 °C, and the scarcity of these
species in warmer tropical and subtropical ecosystems.
Most species of Oidiodendron are acidophilic with pH
optima of 3–5. Their predilection for acidic growth
86
media may explain their abundance in peat (Barron
1962, Sigler & Flis 1998, Rice & Currah 2002, Rice,
unpublished, Thormann et al. 2001, 2002, 2004) as well
as in the acidic soils of coniferous forests (e.g. Morrall
1968, Gams & Söderström 1983). The reported growth
of Oidiodendron species in marine Holothurians and
associated sediments (Pivkin 2000) is unusual, but
tolerance to relatively high salt concentrations does
occur in some species (i.e. O. maius and O. truncatum
see Rice & Currah 2001). The enzymatic abilities and
acidophilic nature of ericoid mycorrhizal Oidiodendron
species may partially explain the success of their host
plants in acidic nutrient-poor soils (Rice & Currah 2001,
in press). The failure of other Oidiodendron species to
form either in vitro or in situ mycorrhizal associations
may be explained by the relatively high pH optima
and different enzymatic abilities of these species. For
example, M. setosum has a high pH optimum and is
unable to utilize either cellulose or tannic acid. These
attributes may partly explain its apparent absence from
in situ ericoid mycorrhizal associations even though
it has been shown to form intracellular coils in these
hosts in vitro (Dalpé 1989).
The predilection shown by many Oidiodendron
species for cold, acidic environments rich in plant,
animal, and fungal debris may occur across the
Myxotrichaceae. In addition to Myxotrichum and
Oidiodendron, the family includes Gymnostellatospora
Udagawa, Uchiyama & Kamiya, Pseudogymnoascus
Raillo, and the widespread anamorphic Geomyces
Traaen (Currah 1985, Sigler et al. 2000). Species of
Geomyces produce small, dry, unicellular, barrelshaped to pyriform arthroconidia in dendritic clusters
at the apices of erect, hyaline conidiophores (Sigler
& Carmichael 1976). Species of Gymnostellatospora,
Myxotrichum, and Pseudogymnoascus produce
small, fusiform ascospores in deliquescent, globose
asci within reticuloperidia (Currah 1985, Sigler et
al. 2000). The physiological requirements of most
Geomyces, Gymnostellatospora, and
species of
Pseudogymnoascus are poorly studied, but there are
reports of cellulolytic activity (Dalpé 1991, Udagawa
et al. 1993, Uchiyama et al. 1995, Sigler et al. 2000,
Udagawa & Uchiyama 2000) and psychrophily
(Uchiyama et al. 1995, Sigler et al. 2000, Udagawa
& Uchiyama 2000). Reports of isolation of the
teleomorphic taxa are rare, but most isolations
have been from decaying plant material and soils
in temperate and cool environments (Udagawa et
al. 1993, Uchiyama et al. 1995, Sigler et al. 2000,
Udagawa & Uchiyama 2000) where corresponding
anamorphs may be common. Myxotrichum chartarum
Kunze : Fr. lacks an anamorph but is also reported to
be psychrophilic (Tribe & Weber 2002).
Myxotrichaceous fungi are common on types of
decaying plant material that are attractive to insects.
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
It has been suggested that the reticuloperidium of
myxotrichaceous fungi is adapted for dispersal by
arthropods (Currah 1985, Currah 1994, Greif & Currah
2003). Dispersal may be effected when the mesh-like
peridial wall is impaled by the body hairs of insects
or other arthropod carriers and plucked away from its
substratum (Greif & Currah 2003). Wind dispersal of
the small, dry conidia of Oidiodendron and Geomyces
is likely, but these conidia may also be adapted for
arthropod dispersal, adhering to carrier exoskeletons
electrostatically (Greif & Currah 2003). Greif and
Currah (2003) hypothesized that small arthropods
may be important in dispersing the conidia locally
while larger insects might disperse the ascocarps over
longer distances to fresh substrates. It is possible that
the reticulate conidiomata of O. myxotrichoides and
the appendages of O. muniellense, O. setiferum and O.
hughesii may function in a similar manner by attaching
masses of conidia to arthropod vectors.
MATERIALS AND METHODS
Isolates were obtained from the University of Alberta
Microfungus Collection and Herbarium (UAMH,
Edmonton, Alberta, Canada), the Mushroom Spawn
Laboratory, Pennsylvania State University (DC,
University Park, PA, U.S.A.), and the Centraalbureau
voor Schimmelcultures (CBS, Utrecht, the
Netherlands).
Information for some species was obtained solely
from the literature. No ex-type or authentic cultures of
O. ambiguum, O. hughesii, O. sulphureum, O. terrestre
or M. emodense are available from culture collections.
Oidiodendron muniellense, O. myxotrichoides, O.
ramosum, and O. reticulatum were published too close
to the completion of this manuscript to be studied
directly. Isolates of O. pilicola and M. striatosporum
from UAMH had degenerated to a point that made
morphological study unreliable. A permanent slide of
the anamorph of M. striatosporum was obtained from
UAMH and used for microscopic measurements and
description.
Morphology
Three replicates each of 40 isolates (16 species, Table
1) were grown as single-point-inoculated cultures
on plates of cornmeal agar [CMA; 17 g Difco-Bacto
corn meal agar (Difco Laboratories, Detroit, MI), 1 L
dH2O] amended with 0.01 % oxytetracycline (Sigma
Chemical Co., St. Louis, MO). Incubation was at room
temperature in the dark. Colonies were measured and
described at 28 d. Colony colour was determined
without reference to a colour standard.
Two separate slide cultures on 10 % (w/v) cereal
agar (CER) (Sigler & Flis 1998) of each isolate were
mounted after 14 d incubation at room temperature in
the dark. Conidiophore colour, texture, and branching
pattern were recorded, as were conidial shape, colour,
and surface ornamentation. Conidiophores were
described as “branched” when conidium-bearing
branches arose from the pigmented apical region of the
conidiophore. Whether branches were dichotomous
or trichotomous was also noted. Conidiophore length
was measured from the point of origin to the end of
the melanized portion. Mean conidiophore lengths
and conidial dimensions were calculated using at
least 10 randomly selected conidiophores and conidia
from each slide culture. Measurements are given as
minimum-(mean)-maximum. Appendages (n = 10)
of O. setiferum were measured from their origin on
the conidiophore to the tip of the longest branch. The
number of appendages per conidiophore was noted.
Observations and measurements were made under oil
immersion using an Olympus BX 50 light microscope
(Olympus Optical Co., Tokyo, Japan). Photographs
were made using an Olympus DP 12 Digital camera
(Olympus Optical Co., Tokyo, Japan).
SEM images of conidia were prepared using
Mycelial plugs (5 mm × 5 mm) from five-wk-old
cultures on CMA. These were freeze-dried in liquid
nitrogen, and viewed on a cryo-stage in a JEOL
#JSM6301FX7V SEM (JEOL U.S.A. Inc., Peabody,
MA).
Physiological Studies
Thirty-eight isolates, representing 15 species, were
used in the physiological tests (Table 1). Light,
temperature and pH tolerance tests follow Rice and
Currah (2001). Unless otherwise stated, enzymatic
assays follow Hutchison (1990) and Rice and Currah
(2001). The effects of three light, six temperature, and
five pH treatments were studied using two replicates
of each isolate grown on CMA. Growth rates (mm/d)
were calculated using two independent measurements
of colony radius of each replicate at 7, 14, 21, and 28
d, and were compared with designated ‘control’ growth
conditions for each factor studied.
Light treatments were diffuse natural daylight,
24 h darkness, and so-called “black light” regime
combining ultraviolet light (Philips F20T12-BL, 20
W; Philips Lighting, New Jersey) and a fluorescent
“growlight” (Sylvania F20T12, 20W; Osram Sylvania,
Mississauga, ON, Canada) (Hambleton & Currah 1997,
Rice & Currah 2001). Temperature treatments were 5,
10, 15, 20, 25, and 30 ºC (± 1.5 ºC). To determine the
effect of pH, isolates were grown on CMA adjusted to
pH 3, 5, 7, 9, and 11 using 1 N hydrochloric acid (HCl)
and 10 % potassium hydroxide (KOH).
For enzyme assays, cultures were grown at room
temperature in the dark on media containing the target
macromolecule with or without an indicator.
87
Species
Strain
Source (original identification where
taxonomically significant)
CEL1
GEL2
LIP3
PEC4
STA5
TAM6
WDG7
Myxotrichum arcticum
UAMH 7565T
Forest soil, U.S.A.
+
+
-
+
+
+
-
M. arcticum
M. cancellatum
M. setosum
UAMH 9243
UAMH 1996
UAMH 3835
UAMH 4535
Decayed spruce, Canada
Soil, Japan
Soil, Canada
Washed mineral soil, Canada
+
-
+
+
+
+
+
+
+
+
+
+
+
+
+
+
-
-
Oidiodendron cerealis
O. cerealis
UAMH 504
UAMH 1522
CBS 349.62
UAMH 6520T
UAMH 6521T
UAMH 6527
Human hair, Canada
Peat soil, Canada
Soil, Italy
Soil, Canada
Soil, Sweden (O. scytaloides)
Soil, Sweden (O. scytaloides)
+
+
+
+
+
+
+
+
+
+
+
+
+
-
+
+
+
+
+
+
+
+
+
+
+
+
-
+
+
-
UAMH 8510
Fir roots, Germany (O. scytaloides)
+
+
+
+
+
-
-
UAHM 9751
Sphagnum, Canada (O. scytaloides)
+
+
+
+
+
+
-
O. flavum
O. fuscum
UAMH 8467A
UAMH 10459T
UAMH 10523
UAMH 1524A
UAMH 8511T
Peat soil, Canada
Mushroom compost, U.S.A.
Mushroom compost, U.S.A.
Peat soil, Canada
Wood pulp, Norway
+
NA
NA
+
-
+
NA
NA
+
+
+
NA
NA
+
+
NA
NA
+
+
+
NA
NA
+
+
+
NA
NA
-
+
NA
NA
-
O. griseum
UAMH 1403A
Wood pulp, Norway
+
+
-
+
+
+
-
O. maius var. citrinum
UAMH 4080
UAMH 8925
UAMH 1525
Wood chips, Canada
Vaccinium roots, Canada
Cedar bog soil, Canada
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
UAMH 7089
UAMH 9275
Ex sclerotia, stream drift, Canada
Ex mycorrhizal root tip, Canada
+
+
+
+
+
+
+
+
+
+
+
+
+
+
UAMH 1540T
UAMH 8920
UAMH 9749
UAMH 10460
Peat soil, Canada
Oxycoccus roots, Canada
Decaying Sphagnum, Canada
Vaccinium roots, Canada
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
-
UAMH 10461
Vaccinium roots, Finland
+
+
+
+
+
+
-
O. chlamydosporicum
O. echinulatum
O. fimicola
O. maius var. maius
RICE & CURRAH
88
Table 1. Sources and enzymatic profiles for Oidiodendron isolates studied.
Table 1. (Continued).
Species
O. periconioides
O. rhodogenum
O. setiferum
O. tenuissimum
1CEL =
cellulose azure.
2GEL =
gelatin.
3LIP = TWEEN
6TAM
7WDG
A
LIP3
PEC4
STA5
TAM6
WDG7
+
+
-
+
+
+
-
UAMH 7289
UAMH 8527T
UAMH 1405A
CBS 401.69
UAMH 5715T
UAMH 1523
UAMH 8513
Humus, Japan (O. echinulatum)
Soil, Canada
Pulp sludge, Norway
Soil, Canada
House dust, Japan
Forest soil, Canada
Leaf litter, Spain
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
-
-
UAMH 1399T
UAMH 8443
UAMH 10464
Forest soil, Canada
Soil, Italy (O. ambiguum)
Decaying spruce, Canada
+
+
+
+
+
+
+
+
+
+
+
+
-
-
-
20 (lipid).
= pectin.
5STA =
T=
GEL2
starch.
= tannic acid medium.
= wood guaiacol (lignin).
ex-type.
= authentic.
+ = positive reaction.
– = negative reaction.
NA = not tested.
89
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
O. truncatum
4PEC
CEL1
UAMH 6084
Source (original identification where
taxonomically significant)
Calypso roots, Canada
Strain
RICE & CURRAH
Polyphenol oxidase (PPO) activity was assessed
using tannic acid medium (TAM), consisting of
5 g tannic acid (BDH Inc., Toronto, ON, Canada)
autoclaved in 200 mL dH2O then combined with a
still-warm, previously autoclaved mixture of 15 g
Difco malt extract, 20 g Difco agar, and 800 mL dH2O
(Rice & Currah 2001) and wood guaiacol medium
(WDG), consisting of 2 g powdered Picea glauca
stem wood, collected locally, plus 18 g Difco agar
and 1 L dH2O, all autoclaved together, with 100 µL
guaiacol (Sigma Chemical Co., St. Louis, MO) then
added to the autoclaved materials (Miyamoto et al.
2000). Mycelial plugs (5 mm × 5 mm) were placed on
plates of TAM and incubated for 48 hr. Darkening of
the medium under the plug was considered a positive
reaction, indicating the ability to degrade soluble
phenolic polymers (Bending & Read 1997). Isolates
were point-inoculated on plates of WDG and incubated
for 5 wk. Red discoloration of the medium around
the mycelium indicated a positive reaction for the
degradation of insoluble phenolic polymers, including
lignin (Miyamoto et al. 2000).
Cellulases were detected using cellulose azure
(Smith 1977, Hutchison 1990, Rice & Currah 2001).
Modified Melin-Norkrans agar (MMN) was made
up as 12 g Difco agar, 3 g Difco malt extract, 1 g dglucose anhydrous (Sigma), 1 g CaCl2, 0.5 g NaCl, 10 g
KH2PO4, 3 g MgSO4·7H2O, and 1 L dH2O. Twenty-ml
volumes were added to 50 mL Pyrex tubes, autoclaved,
and allowed to solidify. A 2 % (w/v) solution of washed
cellulose azure (Sigma) in MMN was autoclaved and
2 mL was pipetted as a layer over the solidified plain
MMN medium in each tube. Reactions were scored
after 5 wk based on the release of azure dye from the
upper layer into the basal MMN layer.
Amylase activity was scored after isolates had
grown for 3 wk on plates of MMN containing 2 g/L
potato starch (BDH Inc., Poole, U.K.). Plates were
flooded with iodine solution (5 g KI, 1.5 g I, 100 mL
dH2O) and decanted after several minutes to reveal a
clear zone around the mycelium in strains positive for
this enzyme.
Pectinase activity was determined after incubation
for 5 wk on MMN containing 5 g/L citrus pectin (Sigma).
After plates were flooded for 6 hr with a 1 % aqueous
solution of hexadecylmethylammonium bromide
(Sigma), a clear zone around the mycelium against
an otherwise opaque background was interpreted as a
positive indication of pectinase activity.
Gelatinase activity was determined using MMN
containing 60 g/L gelatin (Sigma) instead of agar. The
gelatin was dissolved in 900 mL dH2O and autoclaved,
the remaining ingredients were autoclaved in 100 mL
dH2O. The solutions were combined before pouring.
Inoculated plates were incubated for a maximum of
90
5 wk or until decomposition of the gelatin caused
liquefaction of the medium.
Lipase synthesis was determined using MMN
containing 0.1 g/L CaCl2 and 10 mL/L TWEEN 20
[polyoxyethylene sorbitan monolaurate (Sigma)],
added after autoclaving. Isolates were incubated for
16 wk and scored for the presence of macroscopically
visible crystals of the calcium salt of the fatty acid
beneath the mycelium.
RESULTS AND DISCUSSION
Evaluation of Key Characters
Morphology: To date, keys to Oidiodendron species
(Ellis 1971, 1976, Barron 1962, Domsch et al. 1980,
Calduch et al. 2004) have been based exclusively on
morphological characters, especially conidiophore
length, conidial morphology, and cultural characteristics
(Hambleton et al. 1998).
Conidiophores typically are erect and melanized
and they branch at the apices to produce chains of
arthroconidia. Conidiophore length, used regularly to
delimit species, ranges from less than 5 to 500 µm.
However, this character varies significantly among and
even within conspecific isolates. For example, it ranged
from 45 to 455 µm among 21 isolates of O. maius var.
maius and from 123 to 455 µm within a single isolate
(Rice & Currah 2001). Length ranges overlap among
all species except O. cerealis (5–30 µm long) and M.
setosum [typically < 5 µm long, though conidiophores
up to 140 µm long have been observed (Sigler &
Carmichael 1976)]. Consequently, the value of this
character in identification is limited. Nonetheless,
because conidiophore length is a readily observable
character and because ranges are given in all species
descriptions, we have incorporated these measurements
into the dichotomous key. Users should be aware that
this character is most useful when tendencies toward
very short or very long conidiophores are considered
in conjunction with other features.
Conidiophore branching, surface texture and
pigmentation are useful in some instances. Some
species have conidiophores that do not branch within
the melanized portion, while in others, dichotomous,
and occasionally trichotomous, branching occurs. The
conidiophores of most species are either consistently
smooth or faintly and inconsistently asperulate but
those of O. fimicola are scaly in SEM and asperulate
in LM. Oidiodendron cerealis and M. setosum
typically do not produce dark conidiophores; instead,
conidiophores are short (typically < 5 µm long in our
observations of M. setosum, up to 30 µm long in O.
cerealis) and hyaline, resembling vegetative hyphae. In
other species, inconspicuous conidiophores are always
accompanied by larger, melanized conidiophores.
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
The structures commonly called “connectives” are
the remains of the hyphal sleeve in which the conidia
differentiate. This material persists as collapsed
wall material between mature conidia. It is visible
in many species, but its conspicuous presence is not
consistent within or among isolates. This character
is therefore not useful for distinguishing species. On
the other hand, M. arcticum displays a unique form of
conidiogenesis. Termed “geniculate conidiogenesis,”
it produces truncate chains of one or two conidia
borne in whorls at the conidiophore apex, and oriented
perpendicular to the conidiophore axis (Udagawa et al.
1994, Tsuneda & Currah 2004). The ontogeny of these
conidia is difficult to discern using light microscopy,
but the conidiophores involved terminate in a small,
dense head of conidia, easily distinguished from the
more diffuse conidial arrangements produced by
conidiophores terminating in normal branched chains
of arthroconidia.
Conidial size varies little among species. It ranges
from 1.5–3 × 1–2 µm to 3–7 × 2–4 µm, but most
species produce conidia that are 1.5–5 × 1–2.5 µm.
Colour, shape, and ornamentation are variable but
are consistent within species, and therefore are useful
characters. In light microscopy, conidia may appear
hyaline, lightly pigmented, or dark. This trichotomy
is important in our keys. Conidial colour en masse,
as determined using the dissecting microscope, varies
from white to pale grey to green-grey to brown to
yellow. It largely accounts for the characteristic colours
of colonies.
Rice and Currah (2001) found that conidial
ornamentation was consistent among 21 isolates of O.
maius var. maius but distinct from that of a superficially
similar isolate of O. truncatum. This character provided
a clearer distinction between these species than did
conidiophore length and conidial size. Other species
also have distinctive conidial surfaces. For example, the
conidia of O. cerealis are lens-shaped with a thickened
ring and have a rugose (wrinkled) perispore. Conidia
of O. pilicola, O. truncatum, M. cancellatum, and M.
striatosporum are all barrel-shaped with truncate ends
but differ in surface ornamentation. In O. truncatum
and M. cancellatum, conidia have a wrinkled, netlike perispore (resulting in characteristic “reticulate
ornamentation”) while those of O. pilicola are smooth
to minutely asperulate and those of M. striatosporum are
asperulate. Oidiodendron ambiguum, O. echinulatum,
and O. periconioides, all with subglobose to ellipsoidal
conidia, differ in that the conidia of O. ambiguum have
rounded and minutely verruculose (warty) surface
projections, while those of O. echinulatum have larger,
but still rounded, warty projections, and those of O.
periconioides have pointed and spinulose projections.
Oidiodendron muniellense and O. setiferum, which
are morphologically similar to one another, can be
distinguished by conidial ornamentation, which is
asperulate to spinulose in O. muniellense and smooth
to reticulate in O. setiferum. Conidia of other species
may be only slightly asperulate, reticulate, warty, or
dimpled in SEM and look smooth, or nearly so, by
light microscopy. Oidiodendron flavum and O. fimicola
produce a variety of conidial shapes with smooth to
asperulate ornamentation, and can be seen to differ
significantly in this feature only in SEM. Conidial
shapes are illustrated in Table 2.
Unique features, when they occur, may be useful
characters. Examples include the chlamydospores
seen in O. chlamydosporicum, and the melanized
appendages that arise at the conidiophore apices of O.
muniellense, O. setiferum and O. hughesii, and that
make up the peridium-like enclosure of the conidiomata
of O. myxotrichoides. The appendages of O. hughesii
are larger and more highly branched and complex
than those of O. muniellense and O. setiferum, but
are similar to those of O. myxotrichoides in forming a
peridium-like structure surrounding the arthroconidia.
In O. hughesii, peridium-like branches are borne on the
conidiophore apex and do not form a sessile, ascocarplike conidioma.
Colonial morphology, especially colour and the
production of diffusible pigments and exudates, has
also been used as a source of characters. It has the
disadvantages, however, that it can vary according to the
growth medium used and that it is not constant within
isolates of the same species. Cultural characteristics
are used in the keys only when they were reasonably
consistent. Sigler & Gibas (2005–this volume) report
a culture-based method for distinguishing O. maius
from other species.
Physiology: Physiological tests, including enzyme
profiling and tests for tolerance of different growth
conditions, have seldom been used to distinguish
Oidiodendron species (Rice & Currah 2001). Some such
characters do, however, appear to have discriminating
value and are used in our dichotomous key where
appropriate, as well as in the species descriptions and
synoptic key. These characters are presented with the
caveat that only a small number of isolates (1–5 per
species) were tested to obtain profiles. The range of
variation within species and across the genus may be
underestimated.
Neither light nor temperature preferences
discriminated among most species but some minor
distinctions are noted. For example, the growth of O.
echinulatum was suppressed by daylight. Oidiodendron
setiferum grew optimally at 25 ºC and O. truncatum,
M. cancellatum, and M. setosum grew optimally below
20 ºC, with suppressed growth at 25 ºC. All others
grew optimally at 20 ºC. Oidiodendron hughesii and
O. myxotrichoides were not tested here but were
described as psychrophilic, with optimal growth at
15 °C (Udagawa & Uchiyama 1998, Calduch et al.
91
RICE & CURRAH
2002) and O. muniellense grows optimally at 25 °C
(Calduch et al. 2004).
Species fell into two groups with respect to pH
optima. Oidiodendron cerealis, O. chlamydosporicum,
O. flavum, O. fuscum, O. griseum, O. maius, O.
periconioides, O. rhodogenum, O. setiferum, O.
tenuissimum, M. cancellatum, and M. arcticum were
acidophilic (pH optima < 5) while O. echinulatum, O.
truncatum, and M. setosum grew optimally at higher
pH (> 7).
Substrate degradation tests can distinguish
among morphologically similar species (Table 1).
Oidiodendron fuscum, M. cancellatum, and M. setosum
were unable to degrade cellulose azure, but the other
tested species could all do this. Oidiodendron cerealis,
O. periconioides, O. rhodogenum, O. setiferum, M.
arcticum, and M. cancellatum were unable to degrade
TWEEN 20, while this ability varied within O.
chlamydosporicum. Only O. echinulatum was unable
to degrade pectin, while the character was variable
within O. periconioides. Oidiodendron cerealis, O.
flavum, O. fuscum, O. rhodogenum, O. tenuissimum,
O. truncatum, M. cancellatum, and M. setosum were
unable to degrade tannic acid, but O. chlamydosporicum
and M. arcticum varied in this ability. Only O. maius
var. citrinum and O. echinulatum consistently degraded
lignin, while isolates of O. chlamydosporicum varied
in their ability to degrade this substrate. All species
liquefied gelatin, and all but O. truncatum degraded
potato starch.
Keys to Oidiodendron
The numbers given in parentheses after the species name in the keys below refers to the place of the taxon in the
list of descriptions.
Synoptic Key to Oidiodendron
Character
Character State
Species
Conidiomata
Present
O. myxotrichoides (18)
Melanized appendages
Absent
Simple, antler-like
All others
O. muniellense (17)
O. setiferum (22)
Peridium-like
Absent
Present
Absent
Present
Absent
Darkly pigmented
O. hughesii (14)
All others
O. chlamydosporicum (8)
All others
M. arcticum (1)
All others
M. striatosporum (5)
O. cerealis (7)
O. echinulatum (9)
O. flavum (11)
O. muniellense (17)
O. myxotrichoides (18)
O. periconioides (19)
O. tenuissimum (23)
O. truncatum (24)
M. arcticum (1)
M. cancellatum (2)
M. emodense (3)
M. setosum (4)
O. ambiguum (6)
O. chlamydosporicum (8)
O. fuscum (12)
O. griseum (13)
O. maius (15, 16)
O. pilicola (20)
O. fimicola (10)
O. hughesii (15)
O. rhodogenum (21)
O. setiferum (22)
Chlamydospores
“Geniculate conidiogenesis”
Conidial colour
Hyaline
Lightly pigmented
92
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
Character
Conidial ornamentation
Character State
Thickened ring
Reticulate
Species
O. cerealis (7)
M. cancellatum (2)
O. truncatum (24)
Warty or spiny
O. ambiguum (6)
O. echinulatum (9)
O. periconioides (19)
M. striatosporum (5)
O. fimicola (10)
O. flavum (11)
O. hughesii (14)
O. muniellense (17)
O. tenuissimum (23)
M. arcticum (1)
M. emodense (3)
M. setosum (4)
O. chlamydosporicum (8)
O. fuscum (12)
O. griseum (13)
O. maius (15, 16)
O. myxotrichoides (18)
O. pilicola (20)
O. rhodogenum (21)
O. setiferum (22)
O. cerealis (7)
O. ambiguum (6)
O. echinulatum (9)
O. fuscum (12)
O. hughesii (14)
O. muniellense (17)
O. myxotrichoides (18)
O. periconioides (19)
M. cancellatum (2)
M. striatosporum (5)
O. pilicola (20)
O. truncatum (24)
M. arcticum (1)
M. emodense (3)
M. setosum (4)
O. chlamydosporicum (8)
O. griseum (13)
O. maius (15, 16)
O. rhodogenum (21)
O. setiferum (22)
O. tenuissimum (23)
O. fimicola (10)
O. flavum (11)
M. arcticum (1)
M. cancellatum (2)
M. emodense (3)
M. striatosporum (5)
O. ambiguum (6)
O. echinulatum (9)
O. hughesii (14)
O. muniellense (17)
O. periconioides (19)
O. pilicola (20)
O. rhodogenum (21)
Asperulate
Indistinct
Conidial shape
Lens-shaped
Globose-ellipsoidal
Barrel-shaped (truncate)
Subglobose, ellipsoidal or elongate
Variable
Conidiophore branching
Branched
93
RICE & CURRAH
Character
Character State
Melanized
Species
O. setiferum (22)
O. truncatum (24)
O. flavum (11)
O. fuscum (12)
O. griseum (13)
O. maius (15, 16)
O. tenuissimum (23)
M. setosum (4)
O. cerealis (7)
O. chlamydosporicum (8)
O. fimicola (10)
M. setosum (4)
O. cerealis (7)
O. chlamydosporicum (8)
O. fimicola (10)
All others
Conidiophore texture
Highly asperulate
O. fimicola (10)
Colony surface colour
Smooth or minutely asperulate
Yellow
All others
M. setosum (4)
O. maius var. citrinum (15)
M. arcticum (1)
M. cancellatum (2)
M. emodense (3)
O. ambiguum (6)
O. fimicola (10)
O. fuscum (12)
O. griseum (13)
O. maius var. maius (16)
O. rhodogenum (21)
O. echinulatum (9)
O. flavum (11)
M. striatosporum (5)
O. cerealis (7)
O. hughesii (14)
O. muniellense (17)
O. myxotrichoides (18)
O. periconioides (19)
O. setiferum (22)
O. tenuissimum (23)
O. truncatum (24)
O. chlamydosporicum (8)
M. cancellatum (2)
M. setosum (4)
O. hughesii (14)
O. myxotrichoides (18)
O. truncatum (24)
O. chlamydosporicum (8)
O. muniellense (17)
O. setiferum (22)
Unbranched
Variable
Conidiophore pigmentation
Hyaline
Variable
Off-white or grey
Pale brown
Dark brown/green
Optimal temperature
Variable
< 20 ºC
> 20 ºC
Optimal pH
20 ºC
Basic (9–11)
Acidic (3–5)
94
All others
M. setosum (4)
O. echinulatum (9)
O. truncatum (24)
All others
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
Character
Cellulose degradation
Character State
No
Lignin (wood guaiacol) degradation
Yes
Yes
Variable
Lipid (TWEEN 20) degradation
No
Yes
No
Pectin degradation
Starch degradation
Tannic acid degradation
Variable
No
Variable
Yes
No
Yes
Yes
No
Variable
Species
M. cancellatum (2)
M. setosum (4)
O. fuscum (12)
All others
O. echinulatum (9)
O. maius var. citrinum (15)
O. chlamydosporicum (8)
All others
M. setosum (4)
O. echinulatum (9)
O. flavum (11)
O. fuscum (12)
O. maius (15, 16)
O. tenuissimum (23)
O. truncatum (24)
M. arcticum (1)
M. cancellatum (2)
O. cerealis (7)
O. griseum (13)
O. periconioides (19)
O. rhodogenum (21)
O. setiferum (22)
O. chlamydosporicum (8)
O. echinulatum (9)
O. periconioides (19)
All others
O. truncatum (24)
All others
O. echinulatum (9)
O. griseum (13)
O. maius (15, 16)
O. periconioides (19)
O. setiferum (22)
M. cancellatum (2)
M. setosum (4)
O. cerealis (7)
O. flavum (11)
O. fuscum (12)
O. rhodogenum (21)
O. tenuissimum (23)
O. truncatum (24)
M. arcticum (1)
O. chlamydosporicum (8)
95
RICE & CURRAH
Dichotomous Key to Oidiodendron
1a Conidia produced on fertile hyphae arising laterally or terminally from the melanized branches of a
reticuloperidium like conidioma ....................................................................................... O. myxotrichoides (18)
1b Conidia produced on solitary conidiophores; conidiomata absent ....................................................................... 2
2a (1b) Conidiophores hyaline, in some isolates typically < 5 µm long and in others typically < 30 µm long
(exceptional structures may be up to 130 µm long) .............................................................................................. 3
2b (1b) Conidiophores melanized, typically > 5 µm long ......................................................................................... 4
3a (2a) Colonies cream to yellow. Conidia hyaline, subglobose to elongate ...................................... M. setosum (4)
3b (2a) Colonies dark brown to black. Conidia melanized, subglobose to lens-shaped with a thickened
ring ................................................................................................................................................... O. cerealis (7)
4a (2b) Conidiophores bearing melanized appendages at their apices ...................................................................... 5
4b (2b) Conidiophores not bearing melanized appendages at their apices ................................................................ 7
5a (4a) Appendages highly branched and anastomosing to form a reticulate network, 60–300 µm diam.
including peripheral spines. Conidia pale olive brown, produced en masse at the centre of the reticulum
.......................................................................................................................................................O. hughesii (14)
5b (4a) Appendages sparsely branched to form 2–6 setiform hairs. Conidia pale brown, produced from fertile
hyphae arising from the conidiophore apex or from appendage branch points or tips......................................... 6
6a (5b) Appendages straight, up to 60 µm long. Conidia globose to subglobose, asperulate to
echinulate ................................................................................................................................ O. muniellense (17)
6b (5b) Appendages often recurved, up to 130 µm long. Conidia subglobose to elongate or irregular, with smooth
to faintly reticulate ornamentation ...............................................................................................O. setiferum (22)
7a (4b) Fertile hyphae swelling to form chains of vesicles, which form thick-walled, melanized, spiny, globose to
ellipsoidal conidia, 3–6 × 2–4 µm ........................................................................................O. periconioides (19)
7b (4b) Fertile hyphae not forming vesicles. Conidia various ................................................................................... 8
8a (7b) Melanized chlamydospores present, 3–6 × 2–4 µm, borne on repent hyphae and conidiophores.
Conidiophores 5–70 µm long (mean < 20 µm). Conidia hyaline, 1.5–3 × 1–2 µm ...... O. chlamydosporicum (8)
8b (7b) Chlamydospores absent. Conidiophores typically longer than 20 µm. Conidia hyaline or melanized ........ 9
9a (8b) Conidiophores asperulate under light microscopy. Conidia hyaline to pale brown, elongate to barrelshaped or irregular, 3–6 × 2–3 µm .................................................................................................O. fimicola (10)
9b (8b) Conidiophores smooth under light microscopy. Conidia hyaline or melanized, subglobose to ellipsoidal,
elongate, barrel-shaped or irregular .................................................................................................................... 10
10a (9b) Conidia subglobose to barrel-shaped with truncate ends ......................................................................... 11
10b (9b) Conidia globose, ellipsoidal, subglobose, elongate or irregular but neither barrel-shaped nor
truncate .............................................................................................................................................................. 14
11a (10a) Conidia melanized, produced either on conidiophores < 200 µm long or directly from vegetative
hyphae ................................................................................................................................................................ 12
11b (10a) Conidia hyaline, produced on conidiophores < 150 µm long ................................................................ 13
12a (11a) Mature colonies olive-green with yellow margins. Conidia 2–7 × 1.5–2.5 µm, smooth to asperulate with
distinct apical scars, produced on unbranched or dichotomously branched conidiophores <100 µm long or directly
from vegetative hyphae.........................................................................................................M. striatosporum (5)
12b (11a) Mature colonies brown to green-grey, yellow margin absent. Conidia 2–5 × 1–3.5 µm, with distinct
apical scars and reticulate ornamentation, produced on dichotomously branched conidiophores 20–200 µm
long .......................................................................................................................................... O. truncatum (24)
13a (11b) Conidiophores dichotomously or trichotomously branched, 25–100 µm long. Conidia 1.5–3.5 × 1–2.5
96
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
µm, thick-walled, with reticulate ornamentation ................................................................... M. cancellatum (2)
13b (11b) Conidiophores dichotomously branched, 100–150 µm long. Conidia 3–3.5 × 1.5–2 µm, thin-walled,
smooth.......................................................................................................................................... O. pilicola (20)
14a (10b) Conidia melanized ................................................................................................................................... 15
14b (10b) Conidia hyaline ....................................................................................................................................... 17
15a (14a) Conidia globose to broadly ellipsoidal, warty. pH optimum > 7. Conidiophores dichotomously
branched ..................................................................................................................................O. echinulatum (9)
15b (14a) Conidia subglobose to elongate or irregular, with indistinct or asperulate ornamentation. pH optimum
< 7. Conidiophores unbranched ........................................................................................................................ 16
16a (15b) Colonies cream. Conidia subglobose, ellipsoidal, pyriform, or irregular, thick walled, smooth to
asperulate. Conidiophores 25–80 µm long .................................................................................... O. flavum (11)
16b (15b) Colonies brown. Conidia subglobose to elongate, with indistinct to asperulate ornamentation.
Conidiophores 30–250 µm long .......................................................................................... O. tenuissimum (23)
17a (14b) Colonies white to pale grey. Conidia produced in branching chains from fertile hyphae or in truncated
chains (1-2 conidia) in whorls at the conidiophore apices. Conidia subglobose to elongate and irregular, 1.5–3.5
×1–2.5 µm. Conidiophores dichotomously branched .................................................................. M. arcticum (1)
17b (14b) Colonies off-white, grey, or yellow. Conidia produced only in branching chains from fertile hyphae.
Conidia globose to ellipsoidal or subglobose to elongate. Conidiophores unbranched or dichotomously
branched ............................................................................................................................................................ 18
18a (17b) Colonies off-white to grey or green-grey. Conidiophores dichotomously branched. Conidia globose to
ellipsoidal in some isolates and subglobose to elongate or irregular in others ................................................. 19
18b (17b) Colonies off-white to grey, or yellow. Conidiophores unbranched. Conidia subglobose, ellipsoidal or
elongate ............................................................................................................................................................. 21
19a (18a) Colonies off-white to grey, sometimes with diffusible red pigment. Conidiophores 30–85 µm long.
Fertile hyphae dichotomously branched. Conidia subglobose to elongate or irregular, 1.5–5 × 1.5–2 µm, with
indistinct ornamentation ...................................................................................................... O. rhodogenum (21)
19b (18a) Colonies grey or green-grey, red pigment absent. Conidiophores up to 200 µm long. Fertile hyphae
often verticillate. Conidia globose to ellipsoidal, verruculose and 3–4.5 × 2.5 µm in some isolates and subglobose
to short cylindrical, smooth and 1.5–3.5 × 1.5–2 µm in others ........................................................................ 20
20a (19b) Colonies grey. Conidiophores 100–200 µm long. Conidia globose to ellipsoidal, 3–4.5 × 2.5 µm,
verruculose .................................................................................................................................O. ambiguum (6)
20b (19b) Colonies grey or green-grey. Conidiophores 20–200 µm long. Conidia subglobose, ellipsoidal or short
cylindrical, 1.5–3.5 × 1.5–2 µm, smooth ................................................................................... M. emodense (3)
21a (18b) Colonies off-white or yellow. Mean conidiophore length > 100 µm. Conidia produced in long
undulating chains .............................................................................................................................................. 22
21b (18b) Colonies off-white to grey or grey-brown. Mean conidiophore length < 100 µm. Conidia produced in a
dense head of non-undulating chains ................................................................................................................ 23
22a (21a) Colonies yellow to yellow-green. Conidia yellow en masse with a rugose perispore. Positive reaction in
WDG test. Conidiophores 50–230 µm long ............................................................. O. maius var. citrinum (15)
22b (21a) Colonies off-white. Conidia white en masse with an asperulate perispore. Negative reaction in WDG
test. Conidiophores 70–400 µm long ............................................................................ O. maius var. maius (16)
23a (21b) Colonies off-white to grey. Conidiophores 25–130 µm long. Conidia subglobose to cylindrical, 1.5–5
×1–2 µm with an asperulate perispore. Degrades cellulose and tannic acid but not lipid...........O. griseum (13)
23b (21b) Colonies off-white to pale grey-brown. Conidiophores 15–40 µm long. Conidia subglobose to
ellipsoidal, dimpled, 1.5–3 × 1–2 µm with an asperulate to verruculose perispore. Does not degrade cellulose or
tannic acid, degrades lipid ............................................................................................................ O. fuscum (12)
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RICE & CURRAH
Table 2: Conidial shapes in Oidiodendron species.
Conidial shape
Illustration
Species
Subglobose to elongate, thin-walled,
with idistinct ornnamentation
Myxotrichum arcticum, M.
emodense, M. setosum, Oidiodendron
chlamydosporicum, O. fuscum, O.
griseum, O. maius, O. setiferum, O.
rhodogenum
Barrel-shaped, truncate, with distinct
dehiscence scars
M. cancellatum, M. striatosporum, O.
pilicola, O. truncatum
Lens-shaped with a thickened ring
O. cerealis
Globose to elliptical, thick-walled, with
echinulate ornamentation
O. echinulatum, O. muniellense, O.
periconioides
Pyriform to irregular, thick-walled,
with indistinct to asperulate ornamentation (not discernible at this scale)
O. fimicola, O. flavum
Subglobose to elongate, thickwalled, with indistinct to asperulate
ornamentation (not discernible at this
scale)
O. fimicola, O. flavum, O. hughesii, O.
myxotrichoides, O. tenuissimum
98
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
Species Descriptions
1. Oidiodendron anamorph of Myxotrichum
arcticum Udagawa, Uchiyama & Kamiya, Mycotaxon
52: 198–204. 1994. Figs 1–3.
Colonies on CMA 23–25 mm diam at 28 d, white to pale
grey, appressed; reverse dark brown. Conidiophores
abundant, bearing masses of white conidia, smooth,
melanized, dichotomously branched at apex, 20–(75)–
215 × 2–4 µm. Conidiophores in some cases showing
“geniculate conidiogenesis” and terminating in whorls
of truncated chains of 1–2 conidia that are borne
perpendicular to the conidiogenous cell, and in other
cases terminating in hyaline, dichotomously branched
fertile hyphae, 2–3 µm diam, that fragment to form
chains of conidia. Conidia thin-walled, hyaline,
subglobose to elongate and irregular, 1.5–(2.4)–3.5
×1–(1.9)–2.5 µm, asperulate to spinulose under SEM.
Maximal growth at 20 ºC and pH 3. Degrades cellulose,
gelatin, pectin, and starch; UAMH 7565 also degrades
tannic acid.
Specimens examined: U.S.A., George Parks Hwy
Road, Willow, north of Wasilla, Alaska, forest soil,
Figs 1–3. Oidiodendron state of Myxotrichum arcticum. 1.
Small dense head of subglobose to elongate, hyaline conidia
at the apex of a tall, erect, melanized conidiophore [University
of Alberta Microfungus Collection and Herbarium (UAMH)
7565]. Bar = 20 µm. Inset. “Geniculate conidiogenesis.”
Conidiophore apex bearing whorls of truncated chains of one
to two conidia. Arrow indicates connective between chain
of two conidia, arrowheads indicate scars from detached
conidia. Bar = 2.5 µm. Reproduced with permission from
Tsuneda & Currah 2004, fig 28. 2. Branches of fertile hyphae
fragmenting to form subglobose to elongate, asperulate to
spinulose conidia (UAMH 9243). Bar = 10 µm. 3. Chains of
asperulate to spinulose, subglobose to elongate conidia with
short connectives visible between them (UAMH 9243). Bar
= 1 µm.
1992, Udagawa, (UAMH 7565, ex-type). Canada,
Mariana Lake, Alberta, decaying Picea glauca, 1997,
Lumley (UAMH 9243).
Notes: The tall conidiophores and white conidia make
this species superficially similar to O. maius var.
maius but the smaller conidia and the shorter and less
undulate conidial chains of the M. arcticum anamorph
are distinct. The peridial elements of the teleomorph
are morphologically similar to those of sterile
gymnothecia produced by O. maius var. maius (Rice
& Currah 2002). Oidiodendron fuscum, O. griseum,
and M. emodense have similar conidiophore lengths
and also have dense conidiogenous heads. However,
geniculate conidiogenesis is unique to M. arcticum.
Molecular evidence suggests a close relationship
between M. arcticum and O. griseum (Hambleton et
al. 1998, Sigler & Gibas 2005–this volume).
2. Oidiodendron anamorph of Myxotrichum cancellatum Phillips, Grevillea 13:51–52. 1884. Figs 4–6.
Colonies on CMA 11–13 mm diam at 28 d, white
to grey, appressed at margins; reverse purple to
black. Aerial hyphae and conidiophores abundant.
Conidiophores bearing masses of off-white to grey
conidia, melanized, smooth, branched dichotomously
or trichotomously at apex, 25–(50)–100 × 2–4 µm.
Conidia thick-walled, hyaline to lightly melanized at
maturity, subglobose to barrel-shaped, 1.5–(2.6)–3.5
× 1–(1.7)–2.5 µm, reticulately ornamented with a
rugose perispore and bearing conspicuous intercalary
connectives. Maximal growth at 15–20 ºC and pH 5.
Degrades gelatin, pectin, and starch.
Figs 4–6. Oidiodendron state of Myxotrichum cancellatum
(UAMH 1996). 4. Short, erect conidiophores bearing
divergent chains of thick-walled, hyaline to lightly pigmented,
barrel-shaped conidia. Bar = 15 µm. 5. Conidiophores
bearing long chains of subglobose to barrel-shaped conidia.
Bar = 10 µm. 6. Subglobose to barrel-shaped conidia with a
rugose to reticulate perispore. Bar = 1 µm.
99
RICE & CURRAH
Specimen examined: Japan, Tokyo, soil, 1959,
Udagawa (UAMH 1996).
Notes: Dalpé (1991) noted that this species uses
the cellulose in Czapek cellulose agar but in the
present study, the cellulose azure test was negative.
Oidiodendron truncatum is similar but differs in
having melanized conidia and dichotomously branched
conidiophores.
3. Oidiodendron anamorph of Myxotrichum
emodense Udagawa & Uchiyama, Mycoscience 40:
292–296. 1999. Figs 7–8.
Colonies on oat agar (OA) 28–30 mm diam at 28 d
at 25 °C, thin, with submerged vegetative mycelium,
appearing granular due to the production of abundant
ascomata intermixed with aerial hyphae and conidial
heads; at first greyish yellow, becoming greenish grey
or olivaceous black, with clear exudates; reverse dull
green or grey olivaceous; conidiogenesis moderate.
Colonies on potato carrot agar (PCA) 21–22 mm diam
at 28 d at 25 °C, floccose, plane, with thin vegetative
mycelium, producing abundant conidia, greenish grey
or smoke grey; exudate absent; reverse uncoloured to
brownish grey or smoke grey. Conidiophores erect,
arising from vegetative mycelium or aerial hyphae,
straight below, branching at the top to produce an
arborescent, olivaceous brown head; conidiophores
olivaceous brown to dark brown, 25–200 µm long
× 1.5–2.5 µm diam, straight, septate, thick-walled,
smooth or sometimes with black nodes; branches
hyaline to pale olivaceous brown, 10–60 × 2–2.5 µm,
smooth-walled, repeatedly re-branched, frequently
forming a verticillate whorl of 4–6 narrow fertile
hyphae. Fertile hyphae hyaline, cylindrical, 1.2–1.5
µm diam, fragmenting to form conidial chains. Conidia
hyaline, pale greyish green in mass, subglobose,
ovoid, ellipsoidal or short cylindrical, 1.5–3.5 × 1.5–2
µm, almost smooth-walled, truncate at one or both
ends. Connectives sometimes visible between conidia.
Weakly cellulolytic. Reduced growth at 15 °C. Habitat:
grassland soil, Nepal. Description is from Udagawa &
Uchiyama (1999).
Notes: This species is morphologically similar to O.
fuscum, O. griseum, and M. arcticum but M. arcticum
has geniculate conidiogenesis and O. griseum and
O. fuscum have unbranched conidiophores and
dichotomously branched fertile hyphae that are distinct
from the verticillate whorls formed in M. emodense.
4. Oidiodendron anamorph of Myxotrichum setosum
(Eidam) Orr & Plunkett, Can. J. Bot. 41: 1470–1471.
1963. Figs 9–11.
Colonies on CMA 14–15 mm diam at 28 d, cream to
pale yellow, appressed at margins; reverse cream to
orange. Aerial conidia abundant, off-white to yellow
en masse. Conidiophores typically less than 5 µm
long or absent, hyaline to lightly melanized. Hyaline
conidiophores 30–140 µm long were observed
by Sigler & Carmichael (1976). Conidia hyaline,
subglobose to elongate or irregular, 2–(3.6)–5 × 1.5–
(2)–3 µm, produced in dichotomously branched chains
at the conidiophore apices of reduced conidiophores
or directly from vegetative hyphae. Maximal growth
at 15 ºC and at alkaline pH. Degrades gelatin, pectin,
lipid, and starch.
Specimens examined: Canada, Mt. Allen, Kananaskis,
Alberta, soil, 1971, Bissett (UAMH 3835); washed
mineral soil particle, 1971, Bissett (UAMH 4535).
Notes: The absence of melanized conidiophores is
Figs 7–8. Oidiodendron state of Myxotrichum emodense.
Reproduced with permission from Udagawa & Uchiyama
1999, figs 13–14. 7. Dichotomously branched conidiophore
bearing verticillate whorls of fertile hyphae that give rise
to subglobose to ellipsoidal and elongate conidia. Bar = 20
µm. 8. Divergent branches of a conidiophore give rise to
verticils of fertile hyphae and thick-walled, subglobose to
ellipsoidal conidia. Bar = 20 µm.
100
Figs 9–11. Oidiodendron state of Myxotrichum setosum
(UAMH 3835). 9. Short, sparingly branched chains of
elongate conidia produced from vegetative hyphae. Bar =
10 µm. 10. Chains of elongate conidia that collapse upon
desiccation. Bar = 5 µm. 11. Short, unbranched chain of
elongate conidia. Bar = 5 µm.
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
unusual in species of Oidiodendron. This character,
along with the yellow colour of the colony, readily
distinguishes the anamorph of M. setosum from other
species. Molecular evidence supports a presumed
relationship with other species of Oidiodendron
(Hambleton et al. 1998). Oidiodendron sulphureum
(Stalpers 1974), if it were to be re-collected and if it
then turned out to be distinct from O. flavum, would
be similar to M. setosum, but it could be distinguished
based on its darker yellow colonies, the presence of
some melanized conidiophores, and curved fertile
hyphae. More details about O. sulphureum are found
under O. flavum.
5. Oidiodendron anamorph of Myxotrichum striatosporum (Barron & Booth) Sigler, Mycotaxon 4: 385–
388. 1976. Figs 12–13.
≡ Arachniotus striatosporus Barron & Booth fide von
Arx
≡ Byssoascus striatisporus (Barron & Booth) von Arx
(1971) fide Sigler & Carmichael (1976)
Colonies 15–20 mm diam at 14 d at 25 ºC on potato
dextrose agar (PDA) and malt extract agar (MEA);
10 mm diam at 14 d and 25 ºC on Czapek’s synthetic
agar. Colonies bright yellow at first, becoming dark
olivaceous in the center, smooth to slightly floccose,
becoming funiculose; when mature olive-green with
yellow margins, weakly zonate, with edges slightly
irregular to scalloped. A thick turf of conidia is
eventually produced, which may crack irregularly
in older cultures. Colony description is from Barron
& Booth (1966). Conidiophores present or absent;
when present, melanized in the lower one-fifth to
one-third, [12–(35)–62.5 × 2–3 µm], unbranched
or dichotomously branched, with upper portion
Figs 12–13. Oidiodendron state of Myxotrichum striatosporum (UAMH 3758). 12. Conidiophores arising from a
melanized section of the vegetative hyphae. The melanized
lower portions of the conidiophores are unbranched and
give rise to much longer, hyaline upper portions that branch
several times and bear fertile hyphae. The fertile hyphae
fragment to form dark, smooth to asperulate, thick-walled,
barrel-shaped, truncate conidia with apical scars. Bar = 15
µm. 13. Long chains of dark, smooth to asperulate, thickwalled, barrel-shaped to rectangular conidia with darker
apical scars. Bar = 15 µm.
hyaline to subhyaline (up to 50 µm long), branching
dichotomously and producing fertile hyphae, 1–1.5 µm
diam, that fragment to form long, branched chains of
conidia. Conidia barrel-shaped, smooth to asperulate,
truncate with pigmented basal scars, hyaline to yellow
when immature, yellow-brown to brown at maturity,
2–(4)–7 × 1.5–(2)–2.5 µm.
Specimen examined: Canada, Bradford Marsh,
Ontario, soil, 1960, Barron (UAMH 3758), ex-type
Arachniotus striatosporus). Degenerate and no longer
producing conidia. A permanent slide of the type was
obtained from UAMH and used to obtain microscopic
measurements.
Notes: This species is known only from the type but
it is easily distinguished from other Oidiodendron
species based on its olive-green colonies with yellow
margin and by its yellow to brown, truncate, asperulate
conidia.
6. Oidiodendron ambiguum (Peyronel) Malan, Nuovo
Giornale Botanico Italiano 56: 735–737. 1949. Fig
14.
≡ Dicyma ambigua Peyronel fide Malan (1949)
Fig. 14. Oidiodendron ambiguum. Reconstructed from
the descriptions of Peyronel (1914) and Malan (1949).
Tall conidiophore bearing branched fertile hyphae and
verruculose, subglobose to ellipsoidal conidia. Bar = 20
µm.
101
RICE & CURRAH
Colonies “large” (quote from the original description;
dimensions not specified), round, initially ash grey,
later darkening to an intermediate mouse grey.
Vegetative hyphae septate, mostly hyaline and 1–
2.5 µm diam, some melanized and 3–7 µm diam.
Conidiophores arising from areas of dark hyphal
growth that are spaced at relatively regular intervals
in the predominantly hyaline mycelium, erect, rigid,
septate, melanized at maturity, 100–200 × 2–4 µm,
with apices bearing dichotomous primary branches
with many dichotomous, verticillate, or sympodial
sub-branches. Conidia formed in branched chains
along swollen terminal branches, hyaline, globose to
ellipsoidal, minutely verruculose, 3–4.5 × 2.5 µm,
grey en masse, giving the colony its characteristic
colour. Source of isolation: air samples from an alpine
forest. Description is from Peyronel (1914) and Malan
(1949), translated from Italian. [UAMH 8443 (=ATCC
36256) from Italy, soil of snow valley, Mosca (received
from ATCC as O. ambiguum) was reidentified as O.
truncatum].
Notes: Peyronel (1914) was uncertain about the mode
of conidial development and, as a consequence, his
description and figures are unclear. Malan (1949)
considered development to be arthroconidial, and
placed this species within Oidiodendron. Improved
illustrations were provided, but little was added to the
written description. The illustrations provided by Malan
(1949) coupled with isolation data, suggest that this is
likely to be an Oidiodendron species. Neither Peyronel
nor Malan, however, specified a type or deposited
specimens. The only record of O. ambiguum since
Malan is UAMH 8443, which was reidentified by us
as O. truncatum on the basis of its dark, barrel-shaped
conidia with reticulate ornamentation. If encountered
again, O. ambiguum would be distinguished by its
verruculose, hyaline, globose to ellipsoidal conidia.
7. Oidiodendron cerealis (Thüm.) Barron, Can. J. Bot.
40: 594–595. 1962. Figs 15–17.
≡ Trichosporium cerealis Thüm. fide Barron (1962)
≡ Stephanosporium cereale (Thüm.) Swart fide Swart
(1965)
= Oidiodendron nigrum Robak fide Barron (1962)
Colonies on CMA 30–34 mm diam at 28 d, greengrey (CBS 349.62) or pale with clumps of brown to
black conidia (UAMH 504, UAMH 1522), reverse
green-grey to black (CBS 349.62) or dark brown to
black beneath areas of heavy sporulation (UAMH
504, UAMH 1522). Aerial hyphae abundant and
hyaline in UAMH 504 and UAMH 1522 but scarce in
CBS 349.62. Conidiophores short, branched, hyaline
to lightly melanized, 5–(15)–28 × 2–3 µm. Conidia
melanized, in short chains or appearing to be clumped
at conidiophore apex, subglobose to lens-shaped with a
102
Figs 15–17. Oidiodendron cerealis. (UAMH 1522). 15.
Dark, lens-shaped conidia produced in clusters at the apices
of short, hyaline to lightly pigmented conidiophores. Bar =
10 µm. 16. Short conidiophores branched at the apices and
supporting chains of lens-shaped conidia with an extremely
rugose perispore. Bar = 1 µm. 17. Lens-shaped conidia with
a rugose perispore. Bar = 1 µm.
thickened ring and highly rugose (wrinkled) perispore,
2.5–(3.3)–4 × 2–(2.8)–4 µm. Maximal growth at pH
3–5 and 20 ºC. Degrades cellulose, gelatin, pectin, and
starch.
Specimens examined: Italy, Piedmont, alpine meadow
soil, 1962, Dal Vesco (CBS 349.62); Canada,
Edmonton, Alberta, human hair, 1956, Carmichael
(UAMH 504); Bradford Marsh, Ontario, peat soil,
1960, Barron (UAMH 1522).
Notes: This species is unique because of its hyaline
conidiophores and lens-shaped arthroconidia with
thickened rings of cell wall material. These features
led to its placement outside of the genus Oidiodendron.
Molecular analyses, however, support its placement
within Oidiodendron (Hambleton et al. 1998). Its
morphological distinction is significant only at the
species level.
8. Oidiodendron chlamydosporicum Morrall, Can. J.
Bot. 46: 205–206. 1968. Figs 18–19.
= Oidiodendron scytaloides Gams & Söderström
(1983)
Colonies on CMA 9–16 mm diam at 28 d, cream or
pale grey to green-grey or brown, darker at margins,
appressed; reverse cream near margin, becoming dark
brown at centre. Conidia and chlamydospores pale to
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
Figs 18–19. Oidiodendron chlamydosporicum. 18. Elongate,
hyaline conidia produced in short chains at the apices of short,
dark conidiophores and lateral, terminal, and intercalary
dark, subglobose to elongate or irregular chlamydospores
produced singly or in short chains from vegetative hyphae
(UAMH 9751). Bar = 10 µm. 19. Asperulate, elongate conidia
(C) in short chains at a conidiophore apex, intercalary, pitted
chlamydospore (arrowhead) borne on a vegetative hypha
(UAMH 6520). Bar = 1 µm.
brown en masse, produced on repent hyphae at the
surface of the agar or on well developed conidiophores
that are mainly found near the centres of colonies.
Conidiophores (2–3.5 µm diam) intergrading between
structures that are short [3–(10)–17 µm long],
branched, and lightly pigmented to melanized, and
structures that are erect, melanized and 5–(35)–70 µm
long; short and long types both bear chains of hyaline
conidia interspersed with melanized chlamydospores.
Conidia thin-walled, hyaline, globose, subglobose or
elongate, 1.5–(2.5)–5 × 1–(1.7)–2.5 µm, produced
in chains arising from vegetative hyphae or from
conidiophores. Chlamydospores subglobose to barrelshaped or pyriform, thick-walled, melanized, 3–(4)–7
× 2–(3.5)–4µm, abundant, arising singly or in short
chains from vegetative hyphae or conidiophores. In
SEM, conidia minutely asperulate and chlamydospores
pitted. Maximal growth at 20–25 ºC and pH 3. All
isolates tested degrade cellulose, gelatin, pectin and
starch; UAMH 6520, UAMH 8510, and UAMH 9751
degrade lipid; UAMH 6520 and UAMH 6521 degrade
lignin; and UAMH 9751 degrades tannic acid.
Specimens examined: Canada, Candle Lake,
Saskatchewan, boreal forest soil, 1964, Morrall
(UAMH 6520, ex-type); Perryvale, Alberta, Sphagnum
fuscum (Schimp.) Klinggr., bog, Thormann (UAMH
9751, as O. scytaloides); Sweden, humus, Picea abies
(L.) Karst. forest, 1973, Söderström & Bååth (UAMH
6521, ex-type of O. scytaloides); Kongalund, illuvial
soil, Picea abies forest, 1973, Söderström & Bååth
(UAMH 6527, as O. scytaloides); Germany, Freiberg,
roots of dying Abies alba Miller, 1981, Schuler (UAMH
8510, as O. scytaloides).
Notes: Oidiodendron chlamydosporicum was
described as having subglobose to globose, terminal
or intercalary chlamydospores, 4–9 µm diam, and
subglobose, ellipsoidal or cylindrical conidia, 2–6
×1.2–2 µm (Morrall 1968). Oidiodendron scytaloides
was described as having smaller (3–5 × 2.5–3 µm)
ellipsoidal chlamydospores formed in short, terminal,
lateral, or intercalary chains and as having relatively
short (2–4 × 1–2 µm) cylindrical or ellipsoidal conidia
(Gams & Söderström 1983). The ex-type specimens
of the two species, however, are indistinguishable in
terms of chlamydospore shape and size: the shape
ranges from subglobose to barrel-shaped or pyriform
and the size is within the range 3–7 × 2–4 µm in each
isolate. Moreover, conidial size, which overlapped
in the original descriptions, is 1.5–5 × 1–2.5 µm in
all isolates. Oidiodendron chlamydosporicum has
priority over O. scytaloides, which is here relegated
to synonymy. Molecular analyses support their
conspecificity (Hambleton et al. 1998, Calduch et al.
2004).
9. Oidiodendron echinulatum Barron, Can. J. Bot. 40:
595–597. 1962. Figs 20–21.
Colonies on CMA 35–37 mm diam at 28 d, offwhite to tan, floccose, with brown exudate; reverse
dark brown. Aerial hyphae abundant, hyaline.
Conidiophores abundant, bearing masses of brown
conidia, dichotomously branched, melanized, smooth,
12–(35)–88 × 2–5 µm. Additional conidiogenous
branches arising directly from vegetative mycelium,
hyaline, 2–3 µm diam, dichotomously branched,
fragmenting into chains of conidia. Conidia thickwalled, melanized, globose, subglobose or ellipsoidal,
warted at maturity, 2–(3)–4 × 2–(2.6)–3 µm. Growth is
suppressed by daylight. Maximal growth at pH 11 and
20 ºC. Degrades cellulose, gelatin, lipid, starch, tannic
acid and lignin.
Specimen examined: Canada, Ontario, peat soil, cedar
bog, Barron (UAMH 8467, authentic).
Notes: Oidiodendron echinulatum can be distinguished
from other species in the genus by its branched
conidiophores, warted conidia, growth suppression by
Figs 20–21. Oidiodendron echinulatum (UAMH 8467). 20.
Erect conidiophore bearing divergent, branched chains of
thick-walled, warty, dark, subglobose to ellipsoidal conidia.
Bar = 15 µm. 21. Subglobose to ellipsoidal, warty or pitted
conidia. Short connectives are visible between some conidia.
Bar = 1 µm.
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RICE & CURRAH
light, maximal growth at pH 11, and positive WDG
reaction. Oidiodendron periconioides is similar but
has spiny, globose conidia, is WDG negative, and is
not inhibited by light.
10. Oidiodendron fimicola Rice & Currah (2005–this
volume), Figs 22–24.
= Oidiodendron sindenia nomen invalidum fide Rice &
Currah (2005)
Colonies on CMA 19–26 mm diam at 28 d, off-white
to beige or pale grey, appressed with concentric rings
of abundant conidiophores bearing masses of off-white
to beige conidia; reverse olivaceous. Conidiophores
present or absent, branched or unbranched, melanized,
asperulate to scaly, 20–(50)–100 × 2–4 µm. Fertile
hyphae hyaline, 2 µm diam, fragmenting to form short,
dichotomously branched chains of arthroconidia.
Conidia thick-walled, hyaline to light brown, barrelshaped to elongate or irregular, more or less truncate
at one or both ends, asperulate, 3–(4.9)–6 × 2–(2.4)–3
µm.
Specimens examined: U.S.A., St. Louis, Missouri,
mushroom compost, 1976, Beyer (UAMH 10459
= DC 60, as Oidiodendron sp., ex-type); California,
mushroom compost, 1976, Beyer (UAMH 10523 =
DC 61, as Oidiodendron sp.).
Notes: D. M. Beyer labelled material he sent for
deposit in ATCC in 1976 “O. sindenia”, but never
validly published the name. The material deposited at
ATCC was listed in the catalogue under O. sindenia
but it has since died (ATCC, pers. comm.). Beyer sent
us cultures from the Pennsylvania State Mushroom
Spawn Laboratory. One of these, DC 60 (= UAMH
10459), is reportedly from the same collection as the
material deposited in ATCC. Oidiodendron fimicola is
the only Oidiodendron species that has consistently
asperulate conidiophores, a character that distinguishes
it from the morphologically similar O. flavum.
11. Oidiodendron flavum von Szilvinyi, Zbl. Bakt.
Abt. II, 103: 179. 1941. Figs 25–27.
Colonies on CMA 27–28 mm diam at 28 d, cream
to yellow-brown, appressed; reverse dark brown.
Hyphae submerged at colony margins. Conidiophores
abundant, bearing masses of brown to grey conidia,
smooth, unbranched, melanized, 25–(45)–80 × 2–4
µm. Fertile hyphae hyaline, 2–3 µm diam, 2–4 times
dichotomously branched, fragmenting into short
chains of 2–10 conidia. Conidia thin-walled, hyaline
and elongate when immature, becoming globose to
irregular, barrel-shaped, ellipsoidal or pyriform, thickwalled, melanized, smooth to asperulate or dimpled,
2.5–(3.3)–4 x 2–(2.8)–3µm at maturity. Maximal
growth at pH 3 and 20 ºC. Degrades cellulose, gelatin,
lipid, pectin, and starch.
Specimen examined: Canada, Aberfoyle, Ontario, peat
soil, cedar bog, Barron (UAMH 1524, authentic).
Figs 22–24. Oidiodendron fimicola (UAMH 10459). 22.
Short, asperulate conidiophores bearing short chains of
thick-walled, lightly pigmented to dark, barrel-shaped to
elongate or irregular conidia. Bar = 15 µm. 23. Portion of
fertile hypha bearing chains of asperulate, subglobose to
elongate or barrel-shaped conidia with long, thin connectives
visible between conidia. Bar = 5 µm. 24. Fragment of scaly
conidiophore and asperulate, elongate to irregular conidia
with the remnants of connectives remaining at their apices.
Bar = 1 µm.
104
Notes: Oidiodendron flavum is distinguished by the
wide variation in the shape of mature melanized conidia
and by the changes in the shape and pigmentation of
conidia during maturation. Oidiodendron fimicola is
similar in displaying a range of conidial shapes and
pigmentation, but O. flavum is distinct in having
smooth conidiophores and relatively round and
smooth conidia. Molecular evidence suggests a
close relationship between O. flavum and O. griseum
(Hambleton et al. 1998, Lacourt et al. 2001, Sigler &
Gibas 2005–this volume). However, the consistency
of the phenotypic differences between the authentic
strains of the two species merits maintenance of the
two names.
Stalpers (1974) transferred Oedocephalum
sulphureum to Oidiodendron as Oidiodendron
sulphureum and suggested that it was similar or
identical to O. flavum because the conidial dimensions,
given as 3.8–5 × 2.5–3.3 µm, are similar to those
noted by von Szilvinyi (1941) (3.4–5.7 × 2.5–3.4
µm) and because the curved branches on the fertile
hyphae of O. sulphureum were also mentioned by
Barron (1962) in connection with O. flavum. The
brief description provided by Stalpers (1974) does
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
Figs 25–27. Oidiodendron flavum (UAMH 1524). 25. Erect conidiophores bearing short chains of thick-walled, dark, pyriform
to irregular conidia. Bar = 15 µm. 26. Smooth to pitted, subglobose to pyriform conidia borne on fertile hyphae. Bar = 1 µm.
27. Smooth to pitted, subglobose to pyriform or irregular conidia. Bar = 1 µm.
not provide measurements for conidiophore length,
but instead describes the conidiophores as “rather
short or absent, to 3.5 µm wide, with a pigmented,
sometimes roughened basal part and a hyaline
repeatedly branched upper part.” The conidiophore is
not shown in his illustration. No cultures are available
and we have not examined the type so we are unable to
ascertain the precise placement of this species. Based
on Stalpers’ brief description and illustrations, we are
including it under O. flavum. If encountered again,
O. sulphureum would be distinguishable by virtue of
its short conidiophores, sulphur-yellow colonies and
curved fertile hyphae.
12. Oidiodendron fuscum Robak, Saertryk av Nyt
Mag. Naturvidensk. 71: 249–251.1932. Figs 28–30.
Colonies on CMA 24–26 mm diam at 28 d, offwhite to pale grey, appressed; reverse grey-brown
to black. Conidiophores abundant, bearing masses
of off-white to grey conidia, smooth, unbranched,
melanized, 15–(25)–40 × 2–3 µm. Fertile hyphae
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RICE & CURRAH
Figs 28–30. Oidiodendron fuscum (UAMH 8511). 28. Tall, erect conidiophore bearing a dense head of thin-walled, subglobose
to ellipsoidal conidia. Bar = 15 µm. 29. Conidiophore bearing a large, dense head of dimpled, asperulate, subglobose conidia.
Bar = 10 µm. 30. Short chain of subglobose to ellipsoidal, dimpled, asperulate to minutely verruculose conidia. Long connectives
are visible between conidia. Bar = 1 µm.
hyaline, dichotomously branched, fragmenting to form
chains of conidia in a dense head. Conidia thin-walled,
hyaline to lightly pigmented, dimpled, subglobose to
ellipsoidal with an asperulate to minutely verruculose
perispore, 1.5–(2)–3 × 1–(1.5)–2 µm. Maximal growth
at pH 3 and 20 °C. Degrades gelatin, lipid, pectin, and
starch.
Specimen examined: Norway, wood pulp, Robak
(UAMH 8511, ex-type).
Notes: Robak (1932) described O. fuscum as having
106
grey-brown to brown colonies, featuring smooth,
branched or unbranched conidiophores 60–265 µm
long, averaging 110–120 µm, as well as hyaline
to greenish brown conidia 1.6–3.6 × 1.2–2.2 µm,
averaging 2.4 × 1.7 µm. Barron (1962) made O.
fuscum a synonym of O. tenuissimum and described O.
tenuissimum as a variable species with off-white to grey
or brown colonies and hyaline to pigmented conidia.
Nuclear ribosomal sequence analyses indicated that
O. tenuissimum sensu Barron comprises two distinct
lineages. The first, containing UAMH 8511, was
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
designated “O. tenuissimum” and the other lineage
was called “O. sp. nov” (Hambleton et al. 1998).
SEM examination of the conidia of UAMH 8511,
UAMH 8513 (“O. sp. nov”), and the type specimen
of Periconia tenuissima, showed that UAMH 8511
was distinct, while UAMH 8513 looked the same as
the type of P. tenuissima. UAMH 8511 also differs in
cultural morphology from the type of P. tenuissima
(Hambleton, pers. comm.). We regard O. fuscum as
a distinct species on the basis of these morphological
and molecular differences.
Oidiodendron fuscum is morphologically similar to
the anamorphs of M. arcticum and M. emodense, as
well as to O. griseum and O. maius var. maius. It lacks
the geniculate conidiogenesis of M. arcticum and the
verticillate fertile hyphae of M. emodense. On average,
the conidia and conidiophores of O. fuscum are shorter
than those of O. maius var. maius and O. griseum.
Morphological differences between the conidia of
O. fuscum and O. griseum are best observed using
SEM. Oidiodendron fuscum produces subglobose to
ellipsoidal, dimpled, minutely verruculose conidia
while O. griseum has subglobose to cylindrical,
asperulate conidia.
13. Oidiodendron griseum Robak, Saertryck ur
Svensk. Skogvårdsföreningens. Tidskr. 3–4: 440. Figs
31–33.
Colonies on CMA 26–32 mm diam at 28 d, off-white
to pale grey, appressed; reverse dark green-grey to
black. Conidiophores abundant, bearing masses of offwhite to grey conidia, smooth, unbranched, melanized,
25–(60)–130 × 2–5 µm. Fertile hyphae hyaline, 2–3
µm diam, dichotomously branched with acute branch
angles, fragmenting to form long chains, of up to 30
conidia, in a dense fertile head. Conidia thin-walled,
hyaline, subglobose to elongate or cylindrical, 1.5–
(2.5)–5 × 1–(1.5)–2 µm, with an asperulate perispore.
Maximal growth at pH 3 and 20 °C. Degrades cellulose,
gelatin, pectin, starch, and tannic acid.
Specimens examined: Sweden, wood pulp, 1960,
Melin (UAMH 1403, authentic). Canada, Westlock,
Alberta, wood chips and bark, ex logging truck,
Sigler (UAMH 4080); Slave Lake, Alberta, roots of
Vaccinium myrtilloides, Pinus banksiana stand, sand
dune, Hambleton (UAMH 8925).
Notes: Oidiodendron griseum is morphologically
similar to the anamorphs of M. arcticum and M.
emodense, as well as to O. maius var. maius, and O.
fuscum. It lacks the geniculate conidiogenesis of M.
arcticum and has unbranched conidiophores and
dichotomously branched fertile hyphae as opposed
to the branched conidiophores and verticillate fertile
hyphae of M. emodense. Historically, there have
been problems distinguishing isolates of O. griseum
with longer-than-average conidiophores from isolates
of O. maius var. maius (Hambleton & Currah 1997,
Hambleton et al. 1998). However, the fertile hyphae
of O. griseum have narrower branch angles and are
less undulate than those of O. maius var. maius. The
average conidiophore length in O. griseum, < 100 µm,
is less than in O. maius var. maius, where the average
is > 100 µm. Conidia of O. griseum are shorter on
average (< 3 µm) than those of O. maius var. maius
(> 3 µm).
Molecular studies have indicated a complex
relationship between O. griseum and the polyphyletic
O. tenuissimum sensu Barron (Hambleton et al.
1998, Lacourt et al. 2001, Hambleton, unpubl. data).
Hambleton et al. (1998) found that isolates of O.
griseum and O. tenuissimum produced indistinguishable
RFLP patterns but formed distinct clusters based on
ITS sequence data. A similar study (Lacourt et al.
2001), based on a different set of isolates, found no
ITS differences between the two species. Hambleton
(unpublished) has found that a clade encompassing
all sequenced isolates ever identified as O. griseum
and O. tenuissimum sensu Barron is so broad that
it encompasses isolates of all the other sequenced
Oidiodendron species. However, with the division of
O. tenuissimum sensu Barron into O. fuscum and O.
tenuissimum sensu stricto, the similarities between O.
griseum and O. tenuissimum are minimal.
Oidiodendron griseum is morphologically and
physiologically most similar to O. fuscum. According
to Robak’s original descriptions of O. griseum (Melin
& Nannfeldt 1934) and O. fuscum (Robak 1932), the
two differ primarily in colony morphology and show
only slight differences in conidiophore lengths and
conidial dimensions. Robak described the colonies
of O. griseum as green-grey with a dark green-black
reverse (Melin & Nannfeldt 1934) and the colonies
of O. fuscum as brown or grey-brown with a brownblack reverse (Robak 1932). We did not observe these
cultural differences, possibly because different growth
media were used. Both O. griseum and O. fuscum were
similar in having off-white to grey colonies with a
dark grey to black reverse. Furthermore, conidiophore
lengths and conidial dimensions given for the two
species overlap. In O. griseum, the conidiophores
range in length from 40 to 150 µm, averaging 90–100
µm (Melin & Nannfeldt 1934), while those of O.
fuscum range from 60 to 265 µm, averaging 110–120
µm (Robak 1932). Conidia of O. griseum are 2.0–
3.6 × 1.6–2.0 µm, averaging 2.6 × 1.8 µm (Melin &
Nannfeldt 1934), while those of O. fuscum are 1.6–3.6
× 1.2–2.2 µm, averaging 2.4 × 1.7 µm (Robak 1932).
The range in length of conidiophores we observed
(25–130 µm) is smaller than that recorded by Robak
although there is considerable overlap. These different
107
RICE & CURRAH
Figs 31–33. Oidiodendron griseum. 31. Conidiophore bearing long chains of elongate to cylindrical conidia (UAMH 1403).
Bar = 15 µm. 32. Chains of asperulate, subglobose to elongate or cylindrical conidia with short connectives visible between
some of the conidia (UAMH 4080). Bar = 5 µm. 33. Asperulate, subglobose to elongate to cylindrical conidia with intervening
connectives sometimes visible (UAMH 4080). Bar = 5 µm.
ranges might be explained by our use of slide cultures
and different media. Our measurements of mean
conidiophore length (60 µm) were less than Robak’s
(Melin & Nannfeldt 1934). We observed a wider range
of conidial lengths (1.5–5 µm) but mean dimensions
(2.5–1.5 µm) were similar to Robak’s (Melin &
Nannfeldt 1934). Our measurements for O. griseum
fall between the measurements we obtained for O.
fuscum and those given in the original description
(Robak 1932).
In general, the isolates of O. griseum have longer
conidiophores (25–130 µm) than the ex-type of O.
fuscum (15–40 µm). Conidia of O. griseum also differ
from those of O. fuscum under SEM. Our isolates
of O. griseum have relatively long (1.5–5 µm),
cylindrical conidia with an asperulate perispore while
O. fuscum has relatively short (1.5–3 µm), subglobose
to ellipsoidal, dimpled conidia with an asperulate to
minutely verruculose perispore. Additional cultural
108
and molecular differences between O. fuscum and O.
griseum (Sigler & Gibas 2005–this volume) support
recognizing them as distinct.
14. Oidiodendron hughesii Udagawa & Uchiyama,
Can. J. Bot. 76: 1641–1643. 1998. Figs 34–39.
= Oidiodendron reticulatum Calduch et al. (2004)
Colonies on PCA 12–13 mm diam at 21 d at 15 ºC,
3–4 mm diam at 21 d at 25 ºC, green-grey, becoming
dark green to olivaceous black with age, appressed;
reverse uncoloured to brown-grey; exudates absent.
Conidia abundant after 14 d. Colonies on OA growing
more slowly than on PCA, bearing conidiophores
in dense stands; reverse red-brown. Conidiophores
erect, 60–100 × 2.5–3 µm, melanized, unbranched and
smooth-walled below and asperulate and darkened
above, branched and anastomosed to form a globose to
subglobose reticulate network (60–160 µm diam; 250–
280 µm diam when peripheral spines are included).
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
Figs 34–39. Oidiodendron hughesii. Reproduced with
permission from Udagawa & Uchiyama 1998 and
Calduch et al. 2004. Conidiophore and reticulum of
asperulate appendages surrounding a conidial mass (O.
reticulatum; Calduch et al. 2004, fig. 24). Bar = 30 µm.
35. Conidiophore and reticulum of smooth to asperulate
appendages surrounding a conidial mass (O. hughesii;
Udagawa & Uchiyama 1998, fig. 11). Bar = 50 µm. 36.
Simple conidiophore bearing chains of asperulate to
spinulose, ellipsoidal conidia (O. hughesii; Udagawa &
Uchiyama 1998, fig. 17). Bar = 10 µm. 37. Appendages of
the reticulum surrounding the conidial mass. Note that the
asperulate ornamentation does not extend to the apices (O.
hughesii; Udagawa & Uchiyama 1998, fig. 14). Bar = 50
µm. 38. Asperulate hyphae of the reticulum surrounding the
conidial mass. Note that the asperulate ornamentation of the
hyphae extends almost to the apices, but that the tips of the
hyphae are smooth (O. reticulatum; Calduch et al. 2004, fig.
27). Bar = 10 µm. 39. Ellipsoidal, asperulate to spinulose
conidia (O. reticulatum; Calduch et al. 2004, fig. 31). Bar
= 2 µm.
Peripheral spines appendage-like, septate, dark olive
brown, basally asperulate, with 1–2 branchlets arising
near base; apices pointed, lighter in colour and smoother
than the basal region. Fertile hyphae, 1.5–2.5 µm diam,
arising from lateral branches of reticulum elements,
verticillate, hyaline, smooth-walled, fragmenting
to produce conidia. Conidia hyaline to pale olivebrown en masse, oval to ellipsoidal, thick-walled,
asperulate, 2–4 × 1.5–2.5 µm. Simple conidiophores
also produced, melanized, smooth, branched at apex
to produce a dense head of fertile hyphae. Optimal
growth at 15 °C. Habitat: forest soil. Description is
from Udagawa & Uchiyama (1998).
optima. In O. reticulatum, the appendages are
verruculose along their entire length while in O.
hughesii they are smooth at their apices. The conidia
of O. reticulatum are described as pale brown to
olivaceous (Calduch et al. 2004) while those of O.
hughesii are described as hyaline to pale olive brown
en masse (Udagawa et al. 1998). These differences
are slight in light of the similarities between the two
species in colony morphology, reticulum dimensions,
and conidial size, shape, and ornamentation (Udagawa
et al. 1998, Calduch et al. 2004). These minor
differences become even less credible considering that
both species are monotypic. Differences in appendage
ornamentation and conidial size could reflect either
intraspecific variation among isolates or differences
in developmental stage. Calduch et al. (2004) report
that O. reticulatum grows optimally at 25 °C while O.
hughesii grows optimally at 15 °C. However, they also
note that, on some media, growth of O. reticulatum
is similar at 15 and 25 °C (Calduch et al. 2004). It
is plausible that this physiological difference has
been overstated and is due to ecological rather than
phylogenetic differences. Udagawa et al. (1998)
isolated O. hughesii from a cool, temperate, alpine site
while Calduch et al. (2004) isolated O. reticulatum
from a warm, subtropical site in Spain. We feel that the
differences between O. hughesii and O. reticulatum
are not significant at the species level and suggest they
are synonymous. There are no sequence data for O.
hughesii.
Oidiodendron hughesii, O. muniellense, and O.
setiferum are the only species bearing appendages
at the apex of the conidiophore. In O. hughesii, the
appendages are highly branched and anastomose to
form a reticuloperidium-like structure that encloses
the arthroconidial mass, while in the other two species
appendages are more sparsely branched and antlerlike.
15. Oidiodendron maius var. citrinum (Barron) Rice
& Currah, stat. nov., MycoBank MB500256, Figs
40–41.
≡ Oidiodendron citrinum Barron, Can. J. Bot. 40: 597.
1962 (basionym).
Notes: Calduch et al. (2004) distinguish O. reticulatum
from O. hughesii on the basis of appendage
ornamentation, conidial colour, and temperature
Figs 40–41. Oidiodendron maius var. citrinum (UAMH
1525). 40. Tall, erect conidiophore bearing a branched
head of fertile hyphae that fragment to form long chains of
subglobose to elongate conidia. Bar = 15 µm. 41. Subglobose
to elongate conidia with a rugose perispore. Bar = 1 µm.
109
RICE & CURRAH
Colonies on CMA 30–36 mm diam at 28 d, yellowgreen, appressed; reverse pale brown to dark brown in
the centre. Conidiophores abundant, bearing masses of
yellow conidia, tall, unbranched, melanized, smooth,
50–(120)–230 × 2–4 µm. Fertile hyphae hyaline, 2–3
µm diam, dichotomously branched, fragmenting to
form long, undulating chains of conidia. Conidia thinwalled, hyaline, subglobose to elongate, 1.5–(2.8)–5
× 1–(1.8)–2.5 µm, with a rugose perispore. Maximal
growth at pH 3–5 and 20 ºC. Degrades cellulose,
gelatin, lipid, pectin, starch, tannic acid, and lignin.
Specimens examined: Canada, Guelph, Ontario, soil,
cedar bog, Barron (UAMH 1525, ex-type O. citrinum);
6 Mile Lake, Muskoka District, Ontario, ex black
sclerotia in stream drift, March 1991, Malloch (UAMH
7089); Slave Lake, Alberta, ex black mycorrhizal root
tip (Cenococcum Moug. & Fr. sp.) of Arctostaphylos
uva-ursi, Pinus banksiana stand on sand dune, 1998,
Hambleton (UAMH 9275).
Notes: Oidiodendron citrinum is sufficiently similar
to O. maius that it can be considered a subspecific
taxon within O. maius, which was described in the
same publication (Barron 1962). Oidiodendron
maius is much more common in the literature and is
given priority. These two taxa are recognized at the
varietal level, rather than as subspecies, because the
latter term implies the existence of intermediate forms
and differences in distribution (Hawksworth 1974).
There are few data concerning the distribution and/or
possible intergradation of these taxa that would support
designating them as subspecies.
The conidiophores and conidia are similar to O.
maius var. maius but the two can be distinguished on
the basis of colony colour, conidial ornamentation
under SEM, and WDG reaction. Oidiodendron maius
var. citrinum has yellow colonies, conidia with a
rugose perispore, and a positive WDG reaction while
O. maius var. maius has white colonies, conidia with
an asperulate perispore, and a negative WDG reaction.
Molecular analyses indicate that these differences are
probably not significant at the species level leading
to the suggestion that O. citrinum and O. maius are
conspecific or that O. citrinum is a subspecies of O.
maius (Hambleton et al. 1998, Lacourt et al. 2001,
Sigler & Gibas 2005–this volume). Additional
morphological (Sigler & Gibas 2005–this volume)
and physiological (Rice & Currah 2005–this volume)
characters support a close relationship between these
taxa.
16. Oidiodendron maius var. maius (Barron) Rice &
Currah, Figs 42–45.
≡ Oidiodendron maius Barron, Can. J. Bot. 40: 600–602.
1962.
Colonies on CMA 29–38 mm diam at 28 d, off-white
to grey, appressed; reverse pale grey to dark brown in
110
Figs 42–45. Oidiodendron maius var. maius. 42. Extremely
tall conidiophore bearing a head of divergent, branched,
undulating chains of thin-walled, subglobose to elongate
or cylindrical conidia (UAMH 9749). Bar = 40 µm. 43.
Conidiophore apex branching to form fertile hyphae that
fragment to form chains of subglobose to elongate conidia
(UAMH 10460). Bar = 10 µm. 44. Chains of asperulate,
elongate conidia with connectives visible between the
conidia (UAMH 8920). Bar = 1 µm. 45. Branching chain
of asperulate conidia with scars (arrow) showing position
of side branches that have broken free (UAMH 8920). Bar
= 1 µm.
centre. Conidiophores abundant, tall, dark, bearing
masses of white conidia, unbranched, smooth, 70–
(185)–390 × 2–4 µm. Fertile hyphae hyaline, 2–3 µm
diam, dichotomously branched, fragmenting into long,
undulating chains of conidia. Conidia thin-walled,
hyaline, subglobose to elongate, 2–(3.3)–5 × 1–(1.7)–
2.5 µm, with an asperulate perispore. Maximal growth
at pH 3 and 20 ºC. Degrades cellulose, gelatin, lipid,
pectin, starch, and tannic acid.
Specimens examined: Canada, Ontario, soil, cedar
bog, Barron (UAMH 1540, ex-type); Alberta, roots
Oxycoccus quadripetalus Gilib, Picea mariana Miller
bog, Hambleton (UAMH 8920); Perryvale, Alberta,
decomposing Sphagnum fuscum, bog, Thormann
(UAMH 9749); Fort McKay, Alberta, roots Vaccinium
myrtilloides, disturbed sand hill, Hill-Rackette
(UAMH 10460). Finland, Kevo, Research Station,
roots Vaccinium vitis-idaea L., Betula L.-dominated
fjell, Currah (UAMH 10461).
Notes: O. maius var. maius is the only species in the
genus confirmed to act as an ericoid mycorrhizal partner
in nature. It can be distinguished from morphologically
similar species, including O. fuscum, O. griseum, and
the anamorphs of M. arcticum and M. emodense, by
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
its loose head of highly undulating chains of white
conidia, and its long conidiophores (mean >100).
The other species have less undulant fertile hyphae
that branch at more acute angles, resulting in denser
conidial heads, and mean conidiophore lengths less
than 100 µm.
17. Oidiodendron muniellense Calduch, Stchigel,
Gené & Guarro, Stud. Mycol. 50: 161–163. 2004. Figs
46–48.
Colonies on decaying basidiome effuse, hairy, greenish
brown, with the melanized mycelium (hyphae 1–2 µm
wide, septate) partially immersed in the substrate.
Colonies on OA 30–35 mm diam at 4 wk at 25 °C,
brownish beige to brown, flat, velvety, irregularly
folded; reverse dark brown; brownish orange diffusible
pigment produced. Colonies on PCA 26–30 mm at 4
wk at 25 °C, olive-brown, flat; reverse olive-brown.
Colonies on PDA 37–40 mm diam at 4 wk at 25 °C,
greyish orange to greyish brown, slightly funiculose
at centre, radially folded; reverse brownish orange to
yellowish brown. Conidiophores erect, melanized, up
to 200 µm long, 2–3.5 µm wide; upper part bearing
4–6 verticillate appendages. Appendages several
times dichotomously or trichotomously branched,
straight, up to 60 µm long, 1.5–2.5 µm wide at the
base, melanized, thick-walled, septate, and smooth at
the base, becoming pale, thin-walled, and roughened
at the pointed tips. Fertile hyphae terminal or lateral
on the conidiophore apex and appendages, branched,
hyaline, smooth-walled, 1–2.5 µm wide, fragmenting
to form chains of conidia. Conidia globose to subglobose, ochraceous, 1.5–2.5 µm diam, covered with
Figs 46–48. Oidiodendron muniellense. Reproduced with
permission from Calduch et al. 2004. 46. Conidiophore
bearing straight, branched, melanized appendages and a
conidial mass. Bar = 50 µm. 47. Conidiophores bearing
branched, melanized, fertile appendages. Bar = 40 µm. 48.
Globose to subglobose conidia with a reticulate network of
spines. Bar = 5 µm.
a reticulate network of spines as seen under SEM.
Optimal growth at 25 °C. Habitat: decaying basidiome,
Spain. Description is from Calduch et al. (2004).
Notes: This species is morphologically most similar to
O. setiferum but the appendages of O. muniellense are
straighter than those of O. setiferum and are rough at
the tips while those of O. setiferum are smooth. The
conidia of O. muniellense are globose to subglobose
and covered by a reticulate network of spines, causing
them to appear asperulate to echinulate under light
microscopy while those of O. setiferum are subglobose
to ovoid or elongate with a central dimple and covered
with a rugose perispore that causes them to appear
faintly ornamented to smooth under light microscopy.
Notably, the conidia of O. tenuissimum, a species
suggested by molecular evidence to be closely related
to O. muniellense, are very similar to those of that
species: melanized, subglobose, and covered with a
reticulate network of spines.
18. Oidiodendron myxotrichoides Calduch, Gené &
Guarro, Stud. Mycol. 47: 217–218. 2002. Figs 49–50.
Colonies on beech leaves effuse, greenish-brown,
forming patches. Hyphae pale brown to brown, septate,
branched, 1.5–2.5 µm wide. Colonies on OA 30–35
mm diam at 4 wk at 15 ºC, grey-violet to violet, flat,
granulose; reverse dull violet to dark violet. Colonies
on PCA 20–28 mm diam at 4 wk at 15 ºC, green-grey
at the center with white to grey-white margins; reverse
green-grey to dark green. Colonies on MEA 21–29
mm diam at 4 wk at 15 ºC, violet-grey to dark violet,
velvety and radially folded, reverse violet-grey to dark
violet. Colonies on PDA 28–35 mm diam at 4 wk at 15
ºC, grey-green, fasciculate, producing a light orange to
grey-orange diffusible pigment; reverse dark brown.
Conidiomata grey-green to olive, abundant, arranged
in concentric circles on OA and PCA, towards the
periphery on MEA, absent on PDA. Conidiomata
superficial, solitary, confluent, brown to dark brown,
spherical to subspherical, up to 490 µm diam,
consisting of a reticulate network of septate, brown,
thick- and smooth- walled, branched and anastomosed
hyphae up to 4.5 µm wide, radially disposed, from
which fertile hyphae are produced. Peripheral hyphae
up to 250 µm long, spine-like, straight, usually with
shorter and deflected lateral branches, brown to dark
brown, paling towards the apex, smooth- and thickwalled, 2–4 µm wide. Conidiophores of arborescent
fertile hyphae that arise laterally or terminally from
the melanized hyphae of the reticulum, subhyaline,
2–3 µm wide, smooth- and thin- walled. Conidia
globose, subglobose, or broadly ellipsoidal, pale
brown, smooth-walled or very finely rugose and thickwalled at maturity, 2–3 × 1.5–2.5 µm. Optimal growth
at 15 ºC; growth and sporulation reduced at 25 ºC; no
111
RICE & CURRAH
Figs 49–50. Oidiodendron myxotrichoides. Reproduced
with permission from Calduch et al. 2002. 49. Sessile,
reticuloperidium-like conidioma supporting fertile hyphae
that fragment to produce ellipsoidal conidia. Bar = 50
µm. 50. Ellipsoidal conidia with a rugose perispore with
connectives visible between some of the conidia. Bar = 2
µm.
growth at 37 ºC. Habitat: Fagus sylvatica leaf, Santa
Fe del Montseny, Montseny Natural Park, Catalonia,
Spain. Description from Calduch et al. (2002). The
description of O. myxotrichoides appeared while this
manuscript was nearly complete and isolates were not
examined.
Notes: The conidiomata of O. myxotrichoides are
described as sporodochia by Calduch et al. (2002);
however, this term is inappropriate because the
conidiomata lack basal pads of pseudoparenchyma
and do not consist of masses of short conidiophores
(Hawksworth et al. 1995). The structure is probably
best referred to simply as a conidioma. Oidiodendron
myxotrichoides is similar to O. hughesii in producing
conidia within a reticuloperidium-like structure but
in O. hughesii the reticulum forms from anastomosed
appendages at the apex of a solitary conidiophore.
19. Oidiodendron periconioides Morrall, Can. J. Bot.
46: 204–205. 1968. Figs 51–53.
Colonies on CMA 11–18 mm diam at 28 d, dark greengrey to brown; reverse dark red-brown. Orange-brown
exudate produced. Aerial hyphae and conidiophores
abundant. Conidia green-grey to brown en masse.
Conidiophores smooth, melanized and unbranched
at base becoming hyaline and branched at apex, 25–
(85)–175 × 2–4 µm. Fertile hyphae hyaline, branched,
swollen to form chains of vesicles that fragment to
become chains of conidia arising at the conidiophore
apices or laterally from vegetative hyphae. Conidia
thick-walled, dark, spiny at maturity, globose to
ellipsoidal, 3–(3.7)–6 × 2–(3.1)–4 µm. Maximal
growth at pH3 and 20 ºC. Degrades cellulose, gelatin,
pectin (UAMH 6084, UAMH 8527), starch and tannic
acid.
Specimens examined: Canada, Candle Lake,
Saskatchewan, boreal forest soil, 1964, Morrall
(UAMH 8527, ex-type); Nichol Springs, Cypress
Hills, Alberta, root endophyte, Calypso bulbosa (L.)
Oakes, May 1987, Hambleton (UAMH 6084). Japan,
humus, Currah (UAMH 7289).
112
Figs 51–53. Oidiodendron periconioides (UAMH 8527). 51.
Erect conidiophore bearing a dense head of dark, spinulose,
subglobose to ellipsoidal conidia. Bar = 20 µm. 52. Short
chains of spinulose, subglobose to ellipsoidal conidia
forming from swollen vesicles (arrows). Bar = 5 µm. 53.
Spinulose, globose to ellipsoidal conidia. Bar = 1 µm.
Notes: Oidiodendron periconioides is unique in the
genus because it produces chains of globose, vesiclelike swellings that precede the appearance of conidia in
short conidiogenous branches. It is also the only species
of Oidiodendron that consistently produces dark,
spiny, globose to ellipsoidal conidia. Oidiodendron
echinulatum is similar but has more ellipsoidal conidia
with rounded warts on the perispore; it is also WDG
positive while O. periconioides is WDG negative.
20. Oidiodendron pilicola Kobayasi, Bull. Natl. Sci.
Mus. (Tokyo) 12: 424–425. 1969. Fig. 54.
Conidiophores simple, erect, septate, thick-walled,
pale olivaceous brown, 100–150 × 2.5–4 µm. Upper
part branched monopodially (laterally and oppositely)
into fertile hyphae. Fertile hyphae (1.5–2.5 µm diam),
2–3 × branched, hyaline, fragmenting to form conidia.
Conidia hyaline, barrel-shaped, truncate with frills
at both ends, smooth, catenate, apically or laterally
produced, forming dense clusters, 3–3.5 × 1.5–2 µm.
Habitat: decaying human hair; soil. Description from
Kobayasi (1969).
Specimen examined: Sweden, forest soil, 1972,
Nylund (UAMH 7526). Degenerate and not producing
conidia.
Notes: Oidiodendron pilicola resembles O. truncatum,
and the anamorphs of M. cancellatum and M.
striatosporum, in producing conidia that are truncate
at both ends. Conidia of O. pilicola are hyaline, while
those of O. truncatum and M. striatosporum are
dark. Oidiodendron truncatum and M. cancellatum
conidia differ by being reticulate, not smooth, and
M. striatosporum conidia differ by being asperulate.
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
Fig. 54. Oidiodendron pilicola. Reconstructed from
descriptions and illustrations given by Kobayasi (1969). A
tall conidiophore bears oppositely branched, fertile hyphae
that fragment to form branched chains of hyaline, smooth,
barrel-shaped conidia with apical frills. No information was
given to allow placement of septa in the conidiophore stipe
in this conceptual drawing. Bar = 15 µm.
Molecular evidence suggests that this species is
distinct but close to O. chlamydosporicum (Hambleton,
unpubl. data).
21. Oidiodendron rhodogenum Robak, Saertryk av
Nyt Mag. Naturvidensk. 71: 251–255. 1932. Figs 55–
58.
Colonies on CMA 31–34 mm diam at 28 d, off-white
to grey, appressed; reverse brown to grey-brown.
Red diffusible pigment absent on CMA but produced
by UAMH 1405 on OA. Conidiophores abundant,
bearing masses of off-white conidia, smooth, branched,
melanized, 30–(50)–85 × 3–6 µm. Fertile hyphae
hyaline, 2–5 µm diam, dichotomously branched,
fragmenting into long chains of conidia. Conidia
hyaline to lightly melanized, subglobose to elongate
and irregular, 1.5–(2.5)–5 × 1.5–(1.6)–2 µm, with a
rugose perispore. Maximal growth at pH3 and 20 ºC.
Degrades cellulose, gelatin, pectin, and starch.
Specimens examined: Norway, Kistefoss Mills, sludge
in pulp strainers, 1929, H. Robak (UAMH 1405,
authentic). Canada, Ontario, forest soil, 1969, Barron
(CBS 401.69 = UAMH 8508).
Notes: O. rhodogenum has been identified traditionally
on the basis of a red diffusible pigment in culture but
this character is unreliable; pigment production is
Figs 55–58. Oidiodendron rhodogenum (UAMH 1405).
55. Erect, dichotomously branched conidiophore bearing
divergent, branched chains of thin-walled, subglobose to
elongate or cylindrical conidia. Bar = 15 µm. 56. Short chains
of ellipsoidal to elongate conidia branching off a portion of
the conidiophore. Conidia have a rugose perispore. Bar =
5 µm. 57. Chains of ellipsoidal to elongate or cylindrical
conidia with a rugose perispore and connectives visible
between conidia. Bar = 1 µm. 58. Rugose, ellipsoidal to
elongate conidia branching from a fertile hypha. Note scars
left by conidia that have broken free. Bar = 1 µm.
inconsistent within and among isolates. In the absence
of the red pigment, O. rhodogenum is difficult to identify
because the species is not distinctive morphologically or
physiologically. Oidiodendron fuscum and O. griseum
are similar but have unbranched conidiophores. In
addition, the conidia of O. rhodogenum are elongate
to cylindrical with a rugose perispore while those of
O. griseum are asperulate and those of O. fuscum are
dimpled, asperulate, and subglobose to ellipsoidal.
22. Oidiodendron setiferum Udagawa & Toyazaki,
Mycotaxon 28: 234–238. 1987. Figs 59–65.
= Oidiodendron ramosum Calduch et al. (2004)
Colonies on CMA 23–25 mm diam at 28 d, brown,
appressed; reverse green-grey to black (darkest under
areas of conidial production). Conidiophores abundant,
bearing brown masses of conidia and appendages,
smooth, melanized, branching at apex to form
appendages and fertile hyphae, 40–(80)–180 × 2–3 µm.
Fertile hyphae hyaline, penicillate, borne either at the
conidiophore apex or at the tips or branching points of
the appendages, and forming a dense head of conidia.
Appendages (2–4 per conidiophore) produced at the
apices of the conidiophores and subtending masses
113
RICE & CURRAH
of conidia, dichotomously branched, melanized, with
tapered apices, 20–100 × 2–3 µm. Conidia thin-walled,
hyaline to lightly pigmented, subglobose to elongate or
irregular, 1.5–(2.5)–4 × 1–(1.5)–2.5 µm, with a rugose
perispore and a central dimple under SEM. Maximal
growth at 25 ºC and pH 3. Degrades cellulose, gelatin,
pectin, starch and tannic acid.
Specimen examined: Japan, Kobe, house dust,
Udagawa (UAMH 5715, ex-type).
Figs 59–65. Oidiodendron setiferum (UAMH 5715) or reproduced with permission from Calduch et al. 2004. 59. Erect
conidiophore bearing two dichotomously branched appendages and a dense head of thin-walled, hyaline to lightly pigmented,
subglobose to elongate or irregular conidia (UAMH 5715). Bar 15 = µm. 60. Conidiophores bearing long, branched, recurved
appendages subtending central conidial masses (O. ramosum; Calduch et al. 2004, fig. 12). Bar = 100 µm. 61. Apex of
conidiophore bearing four dichotomously branched, recurved, fertile appendages and a small central conidial mass. Arrows
indicate fertile hyphae arising from the appendages (UAMH 5715). Bar = 10 µm. 62. Fertile appendages with conidia arising
from branching points and apices (UAMH 5715). Bar = 10 µm. 63. Penicillate head of fertile hyphae fragmenting to form short
chains of subglobose to ellipsoidal or elongate conidia with a rugose perispore. Connectives are visible between the conidia
(UAMH 5715). Bar = 1 µm. 64. Chains of subglobose to ellipsoidal conidia with a rugose perispore and central dimple visible
on some conidia (UAMH 5715). Bar = 1 µm. 65. Subglobose to ellipsoidal conidia with a rugose perispore and a central dimple
visible on some conidia (O. ramosum; Calduch et al. 2004, fig. 18). Bar = 1.75 µm.
114
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
Notes: Calduch et al. (2004) distinguished O. ramosum
from O. setiferum on the basis of the fertility of the
appendages and conidial ornamentation. Oidiodendron
setiferum was described as having sterile appendages
surrounding the fertile head (Udagawa & Toyazaki
1987) while in O. ramosum, the appendages often give
rise to fertile hyphae from their branching points or
apices (Calduch et al. 2004). Although the matter is
not noted in the original description of O. setiferum,
our SEM observations of the ex-type show that fertile
hyphae and conidia arise from the branching points
and apices of the appendages. The conidia of O.
ramosum are described as smooth to slightly roughened
(Calduch et al. 2004) and those of O. setiferum are
smooth (Udagawa & Toyazaki 1987). However, SEM
examination of O. setiferum shows that the conidia
have a rugose perispore and are no less roughened than
the O. ramosum conidia depicted in the SEM images
of Calduch et al. (2004). Thus, the differences noted by
Calduch et al. (2004) between the original description
of O. setiferum and the features of their taxon, O.
ramosum, cannot be substantiated and O. ramosum is
here considered a synonym of O. setiferum. The two
taxa group together with low to moderate bootstrap
support (54) based on ITS sequence data, suggesting
a close relationship rather than confirming their
distinctness as suggested by Calduch et al. (2004).
Oidiodendron setiferum, O. muniellense and O.
hughesii can be distinguished from others in the
genus by the melanized appendages that subtend the
arthroconidia. See comments under O. hughesii and O.
muniellense.
23. Oidiodendron tenuissimum (Peck) Hughes, Can.
J. Bot 36: 790. 1958. Figs 66–69.
≡ Periconia tenuissima Peck fide Hughes (1958).
Colonies on CMA 18–22 mm diam at 28 d, pale
brown, appressed; reverse dark grey-brown to black.
Conidiophores abundant, arranged in concentric
rings, bearing masses of brown conidia, unbranched,
melanized, 30–(95)–240 × 2–4 µm. Fertile hyphae
hyaline, dichotomously branched, fragmenting to
form chains of conidia. Conidia melanized at maturity,
faintly ornamented, subglobose to elongate, 2–(2.5)–
4 × 1–(2.1)–3 µm. Conidia covered by a reticulate
network of spines as revealed by SEM. Maximal
growth at pH 3–5 and 20 ºC. Degrades cellulose,
gelatin, lipid, pectin, and starch.
Specimens examined: Spain, La Gomera, Canary
Islands, leaf litter, 1995, Castañeda (UAMH 8513).
Canada, Guelph, Ontario, soil, mixed deciduous
forest, 1960, Barron (UAMH 1523).
Notes: See also discussions under O. fuscum and O.
griseum. Both UAMH 8513 and 1523, the two strains
listed above, had previously been identified as O.
tenuissimum sensu Barron, but were subsequently
considered distinct from that species on the basis
of ITS sequences and were labelled “O. sp. nov”
(Hambleton et al.1998). Closer comparison of these
isolates with the type material of Periconia tenuissima
shows that they are indistinguishable from it and are
best accommodated under the name O. tenuissimum.
Oidiodendron tenuissimum has brown colonies,
conidiophores that may exceed 200 µm, and dark,
spinulose conidia as opposed to the off-white or pale
grey colonies, shorter conidiophores (typically less
than 100 µm long), and hyaline, minutely verruculose
to asperulate conidia of O. fuscum. It can be
distinguished from other species of Oidiodendron by
the dark, subglobose to ellipsoidal or elongate conidia
with a reticulate network of spines.
24. Oidiodendron truncatum Barron, Can. J. Bot. 40:
602–604. 1962. Figs 70–72.
Colonies on CMA 30–32 mm diam (UAMH 8443),
38–42 mm diam (UAMH 1399, UAMH 10464), brown
to green-grey, appressed; reverse green-grey to brown.
Conidiophores abundant, clumped, bearing masses
of brown conidia, smooth, branched at apex, more
or less melanized, 18–(75)–180 × 2–4 µm. Conidia
dark at maturity, produced in branched chains at the
conidiophore apices or from vegetative hyphae, barrelshaped to irregular, truncate with distinct apical scars
and reticulate ornamentation, 2–(3.6)–5 × 1–(2.5)–3.5
µm. Maximal growth at 15–20 ºC and pH >7. Degrades
cellulose, gelatin, lipid, and pectin.
Specimens examined: Canada, Guelph, Ontario, soil,
mixed forest, 1960, Barron (UAMH 1399, ex-type);
Slave Lake, Alberta, decaying spruce wood, Lumley
(UAMH 10464). Italy, soil of snow valley, Mosca
(UAMH 8443 = ATCC 36256, as O. ambiguum).
Notes: This species can be readily distinguished from
others in the genus because of its dark, reticulate,
truncate conidia and its inability to degrade starch.
Excluded Species
Oidiodendron robustum Mercado Sierra & Castañeda
Ruiz, Acta Bot. Cubana 33: 3–4. 1985.
The type specimen for this species was not examined
but its description lists conidiophores that are 250–
870 × 7.5–10.5 µm and conidia 5–11 × 2.5–3.2 µm
(Mercado Sierra & Castañeda Ruiz 1985). Both are
much larger than all other species of Oidiodendron
and are more reminiscent of species of Cladosporium.
From the original illustrations and description it is
impossible to determine whether the chains of conidia
are forming by basipetal fragmentation or acrogenous
budding. Based on these ambiguities, this taxon is
excluded from the genus.
115
RICE & CURRAH
Figs 66–69. Oidiodendron tenuissimum. 66. Erect conidiophore bearing a dense head of thick-walled, dark, subglobose to
elongate conidia (UAMH 8513). Bar = 15 µm. 67. Short conidiophore bearing a large, dense head of long chains of spinulose,
subglobose conidia (UAMH 8513). Bar = 10 µm. 68. Spinulose, subglobose to ellipsoidal conidia of dried type material (NYS).
Bar = 2 µm. 69. Subglobose to ellipsoidal conidia with a reticulate network of spines (UAMH 8513). Bar = 1 µm.
116
OIDIODENDRON: SURVEY OF THE NAMED SPECIES AND RELATED ANAMORPHS OF MYXOTRICHUM
Figs 70–72. Oidiodendron truncatum. 70. Erect conidiophore bearing a large, dense head of thick-walled, truncate, dark, barrelshaped conidia with apical frills (UAMH 1399). Bar = 15 µm. 71. Branched chains of barrel-shaped conidia with a rugose
(reticulate) perispore (UAMH 10464). Bar = 5 µm. 72. Barrel-shaped conidia with a reticulate perispore (UAMH 10464). Bar
= 1 µm.
Oidiodendron terrestre Roy & Singh, J. Indian Bot.
Soc. 48: 158–159. 1969.
This species is described as having rapid growth (90
mm in 3 d), hyaline conidiophores, chlamydospores
4.5–14 × 3.5–12.5 µm and ellipsoidal to cylindrical,
one-to two-celled conidia 4–15 × 3–13 µm (Roy
& Singh 1969). This growth rate is much greater,
and conidia much larger than observed in other
Oidiodendron species. In addition, two-celled conidia
are inconsistent with the generic diagnosis. Conidial
ontogeny is unclear from the original description and
illustrations but appears blastic and acropetal rather
than basipetal. The absence of definitive Oidiodendron
characters, along with the large, two-celled conidia,
rapid growth, and hyaline conidiophores, easily
exclude this species from Oidiodendron.
ACKNOWLEDGEMENTS
We thank David Beyer and Joost Stalpers for providing
information on “O. sindenia” and O. sulphureum,
respectively. George Braybrook assisted with SEM. Sarah
Hambleton sequenced several isolates and kindly shared
unpublished phylogenetic trees and SEM images. Lynne
Sigler provided UAMH cultures and permanent slides and
commented on an early ms. draft. Lindsay Elliott, Melissa
Day, Ben Wilson, and Marcie Plishka provided laboratory
assistance. Funding was provided to AVR by a Canadian
Circumpolar Institute C/BAR grant, an Alberta Conservation
Association Challenge Grant in Biodiversity, a Natural
Sciences and Engineering Research Council of Canada
(NSERC) PGS-A and NSERC PGS-B scholarship, and a
University of Alberta Dissertation Fellowship. Additional
support from the NSERC Discovery Grants Programme is
gratefully acknowledged.
117
RICE & CURRAH
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