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Hypoxylon multiforme (Fr.: Fr.) Fr.
Stromata pulvinate, effused at base to slightly constricted, usually coalescent, with
conspicuous perithecial mounds, 4-25 mm diam x 2-5mm thick; surface greyish
sepia (106),
sienna (8) to umber (9) when young, becoming chestnut (40) to black when
mature; brown granules beneath surface with KOH-extractable
pigments sienna (8) to umber (9), rarely with an olivaceous tinge in aged
material; the tissue below the
perithecial layer dark brown to black, up to 4 mm thick.
Perithecia spherical to obovoid, 500-700 µm diam x 600-700 µm
high, discretely surrounded by a carbonaceous stromatal layer.
Ostioles papillate, conical, black, sometimes at the centre of a
discoid depression 150-230 µm diam.
Asci 150-195 µm total length, the spore bearing-parts 64-86 µm
long x 5.5-6 µm broad, the stipes 80-120 µm long, with apical ring
discoid, amyloid, 0.8-1.2 µm high x 2-2.8 µm broad.
Ascospores light brown to brown, ellipsoid-inequilateral,
frequently crescent-shaped, 8.8-10.3 x 3.7-4.9 µm (M = 9.9 x 4.2 µm), with
faint straight germ slit less than spore-length; perispore usually
indehiscent in 10% KOH, smooth, with a thickening on the more convex side.
Anamorph in nature not observed
Habitat: on bark or decorticated wood of branches, trunks or
stumps. Mainly found during this study on Alnus, Betula and
Corylus, more rarely on Rosaceae (Prunus avium, Prunus
spinosa, Sorbus aucuparia) and once on Populus tremula.
Known distribution: Asia, Europe and North America
Specimens examined: FRANCE, Ariège (09):
Montseron, Roquebrune, 01 Aug. 1999, JF-99171, on Prunus
spinosa; Rimont, Las Muros, ruisseau de Peyrau, 10 May 1996,
JF-96052, on Corylus avellana; Rimont, Las Muros, 25 Mar. 1997,
JF-97022, on Alnus glutinosa; Rimont, Grand Bois, 22 Feb.
1999, JF- 99030, on Betula pendula; Saurat, Bois de Lagrié,
16 Aug. 1999, JF-99201, on Sorbus aucuparia. Pyrénées
Atlantiques(64): Sauveterre de Béarn, ile de Sauveterre, 26 Jun. 1999,
JF-99129, on Alnus glutinosa.
Notes: Hypoxylon multiforme is characterized by pulvinate
to widely effused-pulvinate coalescent stromata, with conspicuous
perithecial mounds and conical papillate ostioles, growing on various
hosts. In the field it can be confused with H.
cohaerens and its variety
microsporum, although they both
are constricted at base and restricted to Fagus for the former and
to Quercus and Castanea for the latter. Microscopically,
H. multiforme differs from H.
cohaerens in its faint, less than spore-length germ slit, while it
is conspicuous and spore-length in H.
cohaerens. It will be more easily distinguished from
H. cohaerens var. microsporum
which has smaller ascospores and
vinaceous KOH-extractable pigments.
As pointed out by Professor Rogers (pers. communication) and
Ju et al. (2004), and as
observed in most of our specimens, KOH-extractable pigments of H. multiforme
are frequently with orange shades, even from mature stromata. The taxonomic
value of these variations is unknown but could correspond to chemical
races (Rogers, pers. communication).
As to secondary metabolites
(Quang et al., 2005),
BNT is prevailing in H. multiforme, along with unknown compounds identical
to metabolites found in
H. cohaerens var. microsporum
and
H. michelianum,
which might be azaphilones related to cohaerin A and B isolated from
H. cohaerens.
The four aforementioned species differ
from other members of the Annulata section in having KOH extractable-pigments
that are not dull green (70) and in lacking BNT derivatives
(Quang et al., 2005).
Unlike Ju and Rogers (1996) but
like Petrini and Müller (1986) we
observed in all collections that perispores were mostly indehiscent in 10% KOH.
Moreover, in all collections examined, and in some collections of
H. cohaerens and
H. cohaerens var. microsporum
as well, some perithecia display
ostioles at the centre of a discoid depression, a feature not previously
described and supporting the close relationship of H. multiforme
with other members of the section Annulata erected by
Ju & Rogers (1996).
H. multiforme is widespread in northern hemisphere, having a
wide host range. It is mainly found growing on Betulaceae
(Alnus, Betula, Corylus) and on Rosaceae, but is also reported on Fagus
(Petrini & Müller, 1986) and on various other hosts
(Granmo et al., 1989).
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