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Hypoxylon macrosporum P. Karst.
Stromata on wood effused, elongated, usually with cracks or
wrinkles between the conspicuous perithecial mounds, 8-60 mm long x 4-10
(-18) mm broad x 0.8 mm thick; surface brown vinaceous (84), becoming blackish with age; dark
orange brown granules beneath
surface, with KOH-extractable pigments hazel (88) to isabelline (65); the
tissue below the perithecial layer greyish brown, inconspicuous, extending
upwards between the perithecia.
Perithecia ovoid to obovoid, 250-320 µm diam x 450-600 µm high.
Ostioles opening higher than or at the same level as the
stromatal surface.
Asci 200-260 µm total length x 14-19 µm broad, the spore
bearing-parts 145-190 µm long, the stipes 60-112 µm long, with apical ring
discoid, weakly amyloid, 1.5-2 µm high x 4-6 µm broad.
Ascospores brown to dark brown, ellipsoid-inequilateral to
almost equilateral, often with one end broadened, 20.5-28 x 7-11.5 µm (M =
24.2 x 9.4 µm), with faint straight germ slit less than spore-length and
wall finely dotted; perispore indehiscent in 10% KOH.
Anamorph in nature: not observed. The anamorph in culture
is Sporothrix-like to Nodulisporium-like
(Ju & Rogers, 1996).
Habitat: on wood, less frequently on bark of Salix sp.
Only once recorded on Alnus viridis (Whalley & Petrini 1984).
Known distribution: Europe (France, Greenland, Norway, Russia
, Sweden, Switzerland) and North America (Canada, USA), in glaciated areas.
Specimens examined: FRANCE, Ariège (09): Mérens
les Vals, chemin de l'étang de Bésines, Bois Long, 1950 m. elev., 03
Sept. 2000, JF-00183, on wood of Salix bicolor. SWITZERLAND, Val
Diavel, Albulapass, 2250 m. elev., 03 Sept. 1989, FC-5237-1C, on
Salix glabra (leg. L. Petrini).
Notes: Our record of H. macrosporum is apparently the first published
from France. This fungus is known to have an arctic-alpine distribution,
as confirmed by
Mathiassen (1989) and
Granmo (1999) who described it as very common in
northern parts of Norway. Its southernmost records were from Swiss Alps
(Petrini & Müller 1986) above
1800 m elev., and its occurrence in
central Pyrénées at 1950 m elev., although it could have been expected, is a
nice surprise.
Besides its distinctive ecological requirements, H. macrosporum
is characterized by dark purplish brown stromata with olivaceous brown
KOH-extractable pigments and large ascospores with a faint short germ slit
and a finely dotted wall. This last feature is hardly visible in water and
is more conspicuous in 10% KOH or in chloral. According to
Ju and Rogers (1996)
the epispore is smooth in S.E.M. and dark dots lie beneath
epispore.
Mathiassen (1989)
reports that when growing on bark, H. macrosporum
is erumpent, pulvinate to nearly hemispherical, with 2-3 layers of
perithecia, and surface is more often greyish purple. We did not observed
these features in our collection.
For a time, H. macrosporum has been considered as a variety of
H.
vogesiacum (Pers.) Sacc., as H. vogesiacum (Pers.) Sacc var. macrosporum
Miller (Miller 1961,
Whalley & Petrini 1984). H.
vogesiacum is similar to H. macrosporum in having purplish
grey to vinaceous brown stromata and large ascospores averaging more than
20 µm long.
Mathiassen (1989),
Ju and Rogers (1996) and
Granmo (1999) pointed out their
main differences: H.
vogesiacum lacks the olivaceous brown pigments of H. macrosporum,
and its ascospores are smooth and have a spore-length germ slit at the centre of a darker
band. Moreover it never grows on Salix and its distribution is
hemiboreal (Granmo et al., 1989).
Secondary metabolites of H. macrosporum have not yet been investigated.
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