Hypoxylon macrosporum







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 m diam x 450-600 m high.

Ostioles opening higher than or at the same level as the stromatal surface.

Asci 200-260 m total length x 14-19 m broad, the spore bearing-parts 145-190 m long, the stipes 60-112 m long, with apical ring discoid, weakly amyloid, 1.5-2 m high x 4-6 m broad.

Ascospores brown to dark brown, ellipsoid-inequilateral to almost equilateral, often with one end broadened, 20.5-28 x 7-11.5 m (M = 24.2 x 9.4 m), 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, Arige (09): Mrens les Vals, chemin de l'tang de Bsines, 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 & Mller 1986) above 1800 m elev., and its occurrence in central Pyrnes 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 m 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.