Hypoxylon porphyreum

              

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Hypoxylon porphyreum Granmo.

Stromata pulvinate to effused-pulvinate on bark, 2-8 mm diam x 0.2-0.4 (-0.5) mm thick, rounded but frequently coalescent up to 60 x 19 mm, effused-pulvinate on wood, 2-22 mm long x 1-8 mm broad x 1-3 mm thick; surface purplish brown, with a greyish ochreous pruina (anamorph) occuring on young stromata, more rarely on overmature stromata, with usually inconspicuous perithecial mounds; yellow to citrine yellow granules just beneath surface, more abundant at margins, with KOH-extractable pigments pale brown with an olivaceous shade; the tissue beneath the perithecial layer massive, greyish brown, often more greyish at base, up to 3(-4) mm thick.

Perithecia subglobose to obovoid, 0.2-0.3 mm diam x 0.3-0.45 mm high.

Ostioles lower than the stromatal surface, usually inconspicuous, appearing as black dots under the ochreous pruina, never observed encircled with white material.

Asci 120-170 m total length x 7-9.5 m broad, the spore-bearing part 56-96 m long, the stipes 60-88 m long, with apical ring discoid, amyloid, 0.5 m high x 2.5-3 m broad.

Ascospores brown, ellipsoid-inequilateral, 11-13.5 x 4.5-5.4 m (M = 11.60 x 4.75 m), with a conspicuous spore-length germ slit, straight to frequently sigmoid; perispore dehiscent in 10% KOH, smooth.

Natural anamorph on immature stromata, greyish ochreous, pruinose. Conidiogenous cells hyaline, smooth, 20-28 x 2-2.5 m, conidia ellipsoid, hyaline, 4-5 x 2.5-3 m. Conidiogenous structure Virgariella-like.

Habitat: on bark, more rarely on wood of Quercus.

Known distribution: so far known from Norway and Sweden (Granmo, 1999) and from France (present study).

Specimens examined: FRANCE: Arige (09), Orlu, Les Forges d'Orlu, Cte des Bouychels, 950 m., 16 May 2003, JF-03062, on Quercus petraea. Same location and same substrate, 19 Sept. 2003, JF-03167.

Notes: Hypoxylon porphyreum has been recently described as a new taxon by A. Granmo (1999), based on collections from Norway of a Hypoxylon growing on Quercus and strongly resembling H. fuscum. This report of H. porphyreum is likely to be the first one published from France, and we are grateful to Dr. Granmo for the confirmation of its identification (pers. comm.).

Hypoxylon porphyreum was already known and suspected to be different from H. fuscum long ago (Granmo et al., 1989), but its clear delimitation from H. fuscum was confirmed by chemical data obtained by High Performance Liquid Chromatography (HPLC) (Granmo, 1999; Stadler, pers. comm.) and molecular data (Granmo et al., 1999).

Hypoxylon porphyreum is macroscopically very similar to H. fuscum, but its occurrence on Quercus in boreal areas (South of Norway and Sweden, relict boreal forests in mountainous areas of southern Europe) is a distinctive feature. Although known to be plurivorous (see notes under H. fuscum) the true H. fuscum has never been so far reported from Quercus.

In H. porphyreum, stromatal coloured granules are citrine yellow, while they are orange brown in H. fuscum, yielding more brownish pigments in KOH than H. fuscum. Ascospores are slightly paler, and smaller than in most of collections of H. fuscum, but fall within the size range accepted for this species (Ju & Rogers, 1996; Petrini et al., 1987). Their frequently sigmoid germ slit is noteworthy as it is also a distinctive feature of H. fuscum.

In the field, distinguishing H. porphyreum from H. fuscum relies on more massive stromata for the former, but mainly on host identification. Distinguishing Quercus branches from Corylus ones is complicated by their frequently similar habit. One has to examine the structure of the wood in cross section with a hand lens, Quercus wood has broad vessels 120-190 m diam, while Corylus wood is much more homogenous, with thin vessels up to 40 m diam.

Hypoxylon porphyreum was found in Central Pyrnes in a deciduous forest 950 m. a. s. l., almost the upper limit of Quercus in this area. It was found on small fallen branches of Quercus petraea (up to 5 cm diam), while it has been reported only on Q. robur by Granmo (1999).