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Biscogniauxia anceps (Sacc.) J. D. Rogers, Y.-M. Ju, and F.
Candoussau.
Stromata applanate, irregularly orbicular
5-25 mm diam, often coalescent and then widespread, up to 40 x 20 cm (FC-741), 0.6-0.8 mm thick; surface
dull black,
carbonaceous, when immature covered by a thin pale brown outer stromatal layer
which dehisces progressively; stromatal tissue beneath the perithecia absent.
Perithecia
obovoid, 0.25 mm diam x 0.5 mm high.
Ostioles discoid, umbilicate,
frequently greyish.
Asci cylindrical, short-stipitate, with a discoid to cuboid amyloid
apical ring.
Ascospores unequally two-celled, broadly ellipsoid, constricted
at septum, 14-18 x 7-9 µm, the larger cell hyaline to less frequently dark brown,
the smaller cell hyaline; when pigmented, the larger cell has a straight
to slightly oblique
full-length germ slit.
Specimens examined: FRANCE, Morbihan(56): Guidel, Locmaria, 24 Oct.
2002, JF-02197, on Corylus avellana; Pyrénées Atlantiques (64): Sauveterre de Béarn,
Ile de la Glère,
11 Jun. 1996, JF-96073, on Corylus avellana; same location, 22 Dec. 2002,
FC-740, on Tilia sp.; same location, 22 Dec. 2002, FC-741, on Populus
nigra.
Notes: Biscogniauxia anceps is the only European species of
Biscogniauxia known to have two-celled ascospores. This feature is known
from several tropical or subtropical species (Rogers et al., 1996, Ju
et al., 1998), ascospores of which have a dark-coloured cell and a hyaline
smaller cell. Biscogniauxia anceps is noteworthy in that most
ascospores remain hyaline and nevertheless are able to germinate. For a detailed
discussion about this feature that they consider as neotenic, the reader is
referred to Rogers et al. (1996). Nevertheless, ascospores discharged
through the ostioles upon drying and forming small black masses on the stromatal
surface are mostly pigmented.
Biscogniauxia anceps is a rarely recorded species, so far known in
Europe from France, Italy, Spain and U. K. In France its distribution seems
restricted to areas under oceanic influence such as Bretagne, Landes and Pyrénées
Atlantiques. In Spain it has been recorded in Spanish Basque Country (Françoise
Candoussau, pers. comm.). It is also reported from Honduras and Mexico (Ju et
al., 1998).
Biscogniauxia anceps is found on bark of branches or trunks
of various trees and shrubs, mostly
Corylus avellana, where it can be easily confused with stromata
of Diatrype stigma (Hoffm.) Fr. with which it can grow mixed (JF-02197).
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