After having redefined
narrower limits to the genus Hypoxylon Bull. (Ju & Rogers, 1996),
Rogers & Ju (1996) reinstated the genus Entoleuca in order to accommodate
Hypoxylon mammatum (Wahlenberg) J. H. Miller. Hypoxylon mammatum
was the combination
proposed by Miller (1961) for a fungus known to be a pathogen of numerous
trees including Alnus, Betula, Populus and Salix,
in northern temperate regions of America and Europe. This name was long accepted
and used by most mycologists, although Pouzar (1985) suggested it could be transferred to Entoleuca Syd.,
while Laessųe &
Spooner (1994) considered Entoleuca as a synonym of Rosellinia De
Ju and Rogers (1996) excluded H. mammatum from their concept of Hypoxylon
basing on the following characters which do not fit it: in H. mammatum the stroma is strongly carbonaceous and lacks granules
yielding KOH-extractable pigments, ascal apical apparatus is higher than
broad, ascospores have a germ slit on the concave side and bear a cellular
appendage when immature and perithecia are embedded in a massive white to grey
brown tissue. Moreover, its anamorph is referable to Geniculosporium
Chesters & Greenhalgh, a feature which supports its affinities with other Xylariaceous genera
such as Nemania S. F. Gray, Kretzschmaria Fr., Rosellinia De Not.
and sessile forms of Xylaria Hill ex Schrank rather than with Hypoxylon.
On the other hand, basing on molecular studies and phylogenetic analysis,
Granmo et al. (1999) assume
that affinities of E. mammata rather lie with Hypoxylon sect. Annulata.
After a comparison with the type species E. callimorpha Syd.,
Rogers & Ju (1996) assessed it would be better accomodated in Entoleuca.
A detailed discussion about the relationship of E. mammata (Wahlenberg:
Fr.) Rogers & Ju with other Xylariaceous genera is given in their publication,
along with the distinctive characters of the genus: erumpent multiperitheciate
stromata with a strongly carbonaceous surface, ostioles coarsely papillate,
massive white tissue beneath and between perithecia, anamorph in nature on specialized
pegs that rupture the overlying bark and a virulent bark pathogen activity.
Entoleuca mammata is widespread in northern America and
Europe, with a tendency to be much more frequent in hemiboreal and boreal areas
(Granmo et al., 1989,
Petrini & Müller, 1986).
Therefore its morphology and biology are well documented, unlike E. callimorpha
which is known from only two collections from U. S. A., one of them being
immature (Rogers and Ju, 1996). According to these latter authors, E. mammatum
differs from E. callimorpha in having larger ascospores (19-)22-28(-33)
x 9-10(-12) µm versus (14.5-) 17.5-20.5(-22) x (6.5-) 7-9.5 µm. Fresh collections
of E. callimorpha and culturing data would allow a better delimitation
of these both species.