Biscogniauxia dennisii (Pouzar) Pouzar.
Stromata orbicular to irregularly ellipsoid,
5-20 mm long x 5-12 mm wide x 2-3.5 mm thick, plane to slightly cupulate with
raised margins, restricted at the centre where connected
to the underlying wood; surface shiny black, carbonaceous, covered when immature by an
outer stromatal layer which is externallyochreous and dry, and internally grey,
gelified, pseudoparenchymatous; tissue beneath the perithecia 1.5-2 mm thick, of slightly
whitened cortical host tissue mixed with dark fungal tissue.
tubular, 0.3 mm diam x 1.5 mm high.
Ostioles coarsely papillate.
short-stipitate, with apical ring discoid, amyloid.
brown, 14-18 x 8.8-12.5 µm, broadly ellipsoid, with straight germ slit spore-length.
Specimens examined: FRANCE: Ariège (09): Rimont, Las Muros, 02 Jun.
1996, JF-96074, on Ulmus minor; same location, 18 Aug. 1999, JF-99190,
on Ulmus minor. Haute Garonne (31): Martres- Tolosane, le Moulin, 27 Apr.
2002, JF-02087, on Ulmus minor.
Notes: similar stromata with raised margins and coarsely papillate
ostioles are encountered in two other species: B. querna and B. repanda.
The distinction between these two taxa and B. dennisii relies on ascospore
size and morphology. In B. querna and B. repanda, ascospores have
a circular germ slit while it is unilateral in B. dennisii; ascospores
of B. repanda are smaller than those of B. dennisii, while those
of B. querna are more globose and flattened. Moreover, B. repanda
is mostly found on Sorbus aucuparia and has a hemiboreal to boreal
distribution, while B. dennisii is plurivorous with a predominant occurrence
on Ulmus and Quercus, and is found in temperate areas. Biscogniauxia querna
is known from only one collection on Quercus (Pouzar, 1986). Biscogniauxia
dennisii is so far known from central Europe (Pouzar, 1977, 1986) and southern
Europe ( Candoussau, 1986).