Biscogniauxia has long been known as
Nummularia Tul. & C. Tul., until Miller (1961) placed most of its
members in his section Applanata of Hypoxylon. The current
concept of Biscognauxia was defined by Pouzar (1979, 1986) and
resumed by Ju, Rogers, San Martin & Granmo (1998).
Biscogniauxia is a xylariaceous genus represented
in Europe by ten known species, five of which having applanate stromata and
low margins, i.e., B. anceps,
and thus being likely to be confused with Hypoxylon.
The five other species, i.e.,
B. repanda and
differ in having more or less cupulate
(concave) stromata with conspicuously raised margins.
Biscogniauxia shares with Hypoxylon
discoid ascal apical rings and Nodulisporium-like anamorphs as defined
in Ju & Rogers (1996). It is separated from Hypoxylon primarily in
having bipartite stromata with an outer stromatal layer which disappears on
mature stromata, and in lacking KOH-extractable pigments. Moreover, the stromatal
carbonization is important in Biscogniauxia while it is weak in Hypoxylon
section Annulata and usually absent in Hypoxylon section Hypoxylon
(Ju & Rogers, 1996, Ju et al., 1998). The outer dehiscent stromatal
layer is often overlooked as it is only present on young stromata, remnants
of this layer may be found at margins of mature stromata, but are usually inconspicuous.
It is noteworthy that in Biscogniauxia, the natural anamorph develops
on young stromata either between the outer layer and the stromatal surface, before
the outer layer dehisces (Ju et al.,1998), or on the upper side of
the dehiscing layer and on
stromatal margins (cf. illustrations of B. simplicior).
In the field, applanate stromata of Biscogniauxia
also are easily confused with those of Diatrype Fr. (Diatrypaceae)
and Graphostroma Piroz. (Graphostromataceae). In Diatrype, stromata
differ in lacking carbonaceous tissue and in having a well-developed interperithecial
tissue (entostroma) of usually white granules; moreover, asci are typically
ascospores are yellowish and allantoid, and conidia are scolecosporous (anamorph
Libertella Desm.). Graphostroma is somewhat intermediate between
the Xylariaceae and the Diatrypaceae through a Nodulisporium-like anamorph
recalling the Xylariaceae and light-coloured suballantoid ascospores recalling
Biscogniauxia species develop in bark of trees
and shrubs, especially on dead or dying branches, more rarely on trunks, and
are suspected to be at least weak pathogens (Ju et al., 1998). Therefore
they are to be searched for on dead branches still attached to the trunk, and specimens
of Biscogniauxia found on dead branches lying on the ground are
usually old and their perithecia are empty, unless the branches have broken
Identification of Biscogniauxia mainly relies
on stromatal characters and ascospore size and morphology. Identification of
host is a decisive feature in several species which are apparently host-specific,
i.e., B. cinereolilacina
specific to Tilia sp., B. granmoi
specific to Prunus sp., B. nummularia
specific to Fagus
sylvatica and B. simplicior
specific to Rhamnus catharticus.
For synonyms, see Ju et al., 1998.