Hypoxylon laschii Nitschke.

Stromata pulvinate, erumpent, rounded to slightly elongated, at times coalescent, with inconspicuous to conspicuous perithecial mounds, 2-6 mm diam or up to 7 mm long x 3 mm broad x 1-2 mm thick; surface dark brick (60) to sepia (63) with a rust shade; orange red granules beneath surface and between perithecia, with KOH-extractable pigments orange (7); the tissue below the perithecial layer brownish black, 0.5-1.5 mm thick.

Perithecia spherical to obovoid, 300-450 µm diam x 350-650 µm high.

Ostioles lower to distinctly higher than the stromatal surface, black.

Asci 90-115 µm total length x 7.5-8 µm broad, the spore bearing-parts 56-72 µm long, the stipes 40-48 µm long, with apical ring discoid, amyloid, 0.8-1 µm high x 2-2.8 µm broad.

Ascospores brown to dark brown, ellipsoid-inequilateral with narrowly rounded ends, 8.2-10.2 x 3.5-4.2 µm (M = 9.3 x 3.9 µm), with straight germ slit spore-length, slightly oblique; perispore dehiscent in 10% KOH, smooth.

Anamorph in nature: not observed.

Habitat: on bark of dead or dying branches of Populus sp. still attached to the tree.

Known distribution: North temperate areas: Europe (Finland, France, Germany, Norway, Poland, Sweden) and U.S.A (Ju & Rogers, 1996; Granmo, 1999).

Specimens examined: FRANCE. Ariège (09): Allières, La Souleille, 22 Sept. 1998, JF-98123, on Populus tremula; Rimont, Saurine, 09 Aug. 1998, JF-98096, on Populus tremula; Rimont, Las Muros, ruisseau de Peyrau, 18 Feb. 1999, JF-99037, on Populus tremula; Vernajoul, Pont Fagé, ruisseau de Vernajoul, 31 Aug. 2002, JF-02153, on Populus tremula.

Notes :

Hypoxylon laschii is a very rarely recorded species, this is due to at least three reasons :

-it is restricted to dying branches of Populus sp. that are still attached to the tree in stations with a high level of humidity, and therefore can only be collected, in most cases in poor condition, when those branches are broken off by the wind or by the snow. This peculiar ecology recalls what is observed in H. cercidicolum and H. intermedium, and in other xylariaceous genera (Biscogniauxia, Entoleuca).

- its small stromata are very inconspicuous and, in the field, are easily confused with those of H. perforatum or H. rubiginosum.

- in spite of an active search in suitable stations, it seems to occur rarely and very sparsely.

Beside its peculiar ecology, H. laschii differs from H. rubiginosum in having small, erumpent, pulvinate stromata with a thick basal tissue and often prominent ostioles. Moreover its ascospores are smaller and their slightly oblique germ slit might be a distinctive feature if this observation is confirmed.

It differs mainly from H. perforatum in having orange KOH-extractable pigments, but also in having larger perithecia, slightly smaller ascospores and in lacking a conspicuous ring of white substance around the ostioles.

Hypoxylon laschii belongs to the rubiginosum chemotype, with mitorubrinol as prevailing compound, along with orsellinic acid, but only traces of rubiginosin A (Stadler et al., 2004b).

Hypoxylon laschii remains a poorly known species, needing more records of fresh material. We hope that the knowledge of its ecological requirements will contribute to make it more often collected.