45
KEY TO THE BRITISH SPECIES OF HYPOXYLON
A.I.S. Whalley
Hypoxylon Bull. ex Fr. is one of the largest genera in the Xylariaceae,
its species have a world wide distribution and it is fairly well represented in
Britain. All Hypoxylon species are wood inhabitants and many of them are
weak parasites although the initial infection in a live tree usually follows injury
by drought, fire, or storm. Only a few species are limited to specific host plants
but some display host preferences such as H. [ragiforme on Fagus. H. argillaceum
on Fraxinus, and H. udum on Quercus.
The previous accounts of British species of the genus (Miller, 1930; 1932a;
1932b; Dennis, 1968; Whalley and Greenhalgh, 1973), are now incomplete
whilst Miller's 1961 monograph of the world species contains much unnecessary
information for ready identification of British species. The following key has
been constructed with the intention of providing an easy route for the identification of the thirteen species and one variety of Hypo xylon occurring in
Britain. Where possible field characters are given, but in many cases ascospore
dimensions must be ascertained before identity can be confirmed.
The nomenclature used follows Miller (1961)
KEY
1.
2.
3.
4.
5.
6.
7.
Stromata applanate, restricted or indefinitely effused, black and carbonaceous at maturity. Ostioles papillate often becoming punctate with age.
Ascospores 10 - 16 x 6 - 10J.,Lm. Chiefly on Fagus
..................................................................... H. nummularium Bull. ex Fr.
Stromata globose, semiglobose, pulvinate or widely effused
2
Ostioles umbilicate (perithecial necks flush with the surface of the stroma,
the ostioles appearing as small pores)
3
Ostioles papillate (perithecial necks project beyond the stromal surface
forming distinctive protuberances)........................................................... 7
Stromata indefinitely effused or occasionally pulvinate when erumpent
from bark, usually red or purple-red in colour. Ascospores 9 - 13 x 4 H. rubiginosum PeTS. ex Fr.
7 um. Chiefly on Fraxinus
(This is a very common species and it is extremely variable. In moist
situations the colour is red or purple red but when growing under dry
conditions of high light intensity it may be pale brown. On small branches
with bark the stromata are usually small and pulvinate and may be mistaken
for H. fuscum.)
Stromata globose, semiglobose, or pulvinate, strongly coloured
4
Stromata brick red or orange, some times black when very old
5
Stromata clay-colour or purple, never brick red or orange
6
Ascospores greater than 10 J.,Lm. Chiefly on Fagus
.............................................................. H. [ragiforme (PeTS. ex Fr.) Kickx
Ascospores less than 10 J.,Lm. On a variety of hosts but never on Fagus
................................................................................... H. howeianum Peck
Stromata globose to semiglobose, clay-colour. Ascospores greater than
15 J.,Lm. On Fraxinus
H. argillaceum Pers. ex Beck.
Stromata pulvinate, purple. Ascospores less than 15 J.,Lm. Chiefly on Corylus
................................................................................ H. fuscum Pers, ex Fr.
Stromata initially coloured and at maturity remaining coloured or becoming blackened
8
Stromata initially light grey to white, at maturity black and carbonaceous
................................................................................................................ 10
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8.
9.
10.
11.
12.
13.
Stromata initially red or red-brown, at maturity dark purple - brown or
black
9
Stromata initially straw-colour, later dark brown, eetostroma characteristically blood red beneath the surface. Ascospores 7 - lOx 3.5 - 4.5;um.
On Fagus
H. rutilum Tul.
H. multiforme Fr.
Ascospores 8 - 12 x 3.5 - 6 11m. Chiefly on Betula
Ascospores 9 - 12 x 4 - 5 11m. Chiefly on Fagus
............................................................................ H. cohaerens Pers. ex Fr.
(H. cohaerens and H. multiforme both have similar ascospore dimensions
which can make separation difficult. However, H. multiforme is commonly
found on Betula and Alnus, occasionally on Corylus but H. cohaerens is
almost exclusively found on Fagus.)
Stromata widely effused
II
Stromata subglobose with one to several perithecia
13
Stromata 2 - 4 mm thick, easily separated from the substrate. Ascospores
H. deustum (Hoffm. ex Fr.) Grev.
25 - 35 x 7 - 12 11m
(= Ustulina deusta (Fr.) Petrak.)
Stromata 1 - 2 mm thick, firmly adherent to substrate, ascospores under
20 11m in length
12
Ascospores 10 - 17 x 5 - 811m
H. serpens (Pers. ex Fr.) Kickx
(This species is extremely variable with a thick undulating stroma when
growing on bark but on decorticated wood the stroma is usually thin and
smooth.)
Ascospores 8 - lOx 4 - 5 11m
H. serpens var. effusum (Nits.) Mill.
(The only British record is from Leckford Estate, Stockbridge, Hampshire
1972, see Dennis, 1974.)
Ascospores broadly elliptic never greater than 25 11m
................................................................ H. confluens (Tode ex Fr.) West.
(= H. semi-immersum Nits.)
Ascospores oblong with germ-pore, never less than 25 11m
H. udum Pers. ex Fr.
(The perithe cia of this species and of H. confluens have their lower halves
immersed in the wood, the depth of immersion depending on the hardness
of the wood, and when the surrounding stroma is poorly developed may be
confused with R osellinia.)
FOOTNOTES
I.
2.
H. stygium (Lev.) Sacco has been collected from the Chatsworth House
Conservatory (Herb. K. no. 785, under Sphaeria marginata Schw.) but as
pointed out by Miller (I 932) it is a tropical species which was probably on
imported wood and is not considered to be native.
There are excellent descriptions of many of the British species by Anders
Munk in his account of Danish Pyrenomycetes.
REFERENCES
DENNIS, R.W.G. (I 968) British Ascomycetes. Lehre: Cramer.
DENNIS, R.W.G. (I 974) New or interesting British micro-fungi, 11, Kew Bulletin
29,157-179.
MILLER, J.H. (1930) British Xylariaceae I. Transactions of the British Mycological Society 15, 134-154.
MILLER, J.H. (I932a) British Xylariaceae 11. Transactions of the British Mycological Society 17, 125-135.
MILLER, J.H. (I 932b) British Xylariaceae III. Transactions of the British Mycological Society 17, 136-146.
47
MILLER, l.H. (1961) A monograph of the world species of Hypoxylon. Athens,
U.S.A.: University of Georgia Press.
MUNK, A. (1957) Danish Pyrenomycetes. Dansk Botanisk Arkiv 17. 1-491.
WHALLEY, A.l.S. & GREENHALGH, G.N. (1973) Numerical Taxonomy of
Hy poxylon II. A key for the identification of British species of Hypoxylon.
Transactions of the British Mycological Society 61,455-459.
TABLE 1.
BRITISH SPECIES OF HYPOXYLON:Ascospore Dimensions
(J.lm)
Species
Length
Width
*
H. fragiforme
11 - 15
5-8
13.20 x 5.90
H. howeianum
6-9
3-4
7.65 x 3.30
H. argillaceum
15 - 25
8 - 11
20.57 x 9.35
H. [uscum
12 - 15
5-8
13.50 x 6.65
H. rubiginosum
9 - 13
4-7
11.10 x 4.95
H. cohaerens
9 - 12
4-5
10.21 x4.33
H. multiforme
8 - 12
3.5 - 6
9.60 x 4.50
H. rutilum
7 - 10
3.5 - 4.5
8.47 x 3.84
H. confluens
15 - 22
8 - 12
18.95 x 9.60
H. udum
26 - 37
9 - 13
30.80 x 10.78
H. serpens
10 - 17
5-8
12.35 x 5.60
H. serpens var. effusum
8 - 10
4-5
H. deustum
25 - 37
7 - 12
29.75 x 12.60
H. nummularium
10 - 16
6 - 10
12.80 x 7.40
Average Size
* Based on a minimum of 100 ascospores taken from different collections.
Anthony Whalley