Biscogniauxia simplicior Pouzar.
Stromata cupulate to applanate, discoid to irregularly ellipsoid,
8-22 mm long x 6-20 mm broad x 3-8 mm thick, constricted at base, with raised
and crenate margin; outer dehiscing layer crust-like, roughened to pustulate,
greyish to ochreous, fugacious; stromatal surface dull black to black, carbonaceous, usually with
a grey to ochreous line along the margin; tissue beneath perithecia up to 7
mm thick, greyish with black carbonaceous granules.
0.3-0.4 mm diam x 0.9-1.1 mm high; ostiolar canal up to 0.6 mm long, lined with
Ostioles discoid, umbilicate, freaquently greyish.
with discoid amyloid apical ring.
Ascospores brown, ellipsoid with frequently
narrowly rounded ends, 11-16 x 5-5.5 µm, with straight germ slit spore-length.
Natural anamorph on immature stromata, ochreous to grey, on the internal
side of stromatal margins and on the upper side of the outer dehiscing
layer. Conidiogenous structure Nodulisporium-like, with conidiophores
pale brown, roughened, 4-7 µm broad; conidiogenous cells subhyaline, 23-30 x
3.5 µm; conidia narrowly ellipsoid, hyaline, 8-10 x 2.5-3 µm.
Specimens examined: FRANCE, Ariège (09): Rimont, Grillou, 16 Apr.
1996, JF-96059, on Rhamnus catharticus; Rimont, Las Muros, 19 Aug. 1999,
JF-99189, on Rhamnus catharticus; Rimont, Grillou, 11 May 2001, JF-01090,
on Rhamnus catharticus; Rimont, Grillou, 11 Dec. 2002, JF-02238, on Rhamnus catharticus.Tarn (81): Escoussens, La Blancariée, 07 Feb.
2002, JF-02026, on Rhamnus catharticus.
Notes: Macroscopically, B. simplicior is similar to other taxa
in Biscogniauxia with somewhat cupulate stromatal surface and raised
margin: the closest taxon is B. repanda, which differs from B.
simplicior in shorter ascospores with a bilateral germ slit and host preference
for Sorbus. Biscogniauxia marginata shares with B. simplicior
umbilicate ostioles, but differs in subglobose, blackish brown ascospores with
a sigmoid germ slit.
Biscogniauxia simplicior is an European taxon known from Bulgaria,
Czech Republic and Germany (Pouzar, 1979, 1986), which is easily found in suitable
situations in central Pyrénées. Its occurrence is closely linked to the presence
of Rhamnus catharticus, but our experience shows that it does not follow
its host in all situations. Rhamnus catharticus is able to grow from
very xerophytic rocky forests to alluvial forests in very damp situation. Biscogniauxia
simplicior is never found in the latter situation and rarely found in very
dry locations, but is common in hot, medium-dry rocky deciduous forests, on
Rhamnus catharticus associated with Quercus pubescens, providing
that the level of atmospheric humidity is high enough.
Biscogniauxia simplicior is usually found on living or dying stems
of Rhamnus catharticus and is likely to be pathogen, as all shrubs on
which it develops die within a few years.