Hypoxylon stygium (Lév.) Sacc. var. annulatum
(Rehm) Ju & Rogers.
Stromata pulvinate to hemispherical on bark, erumpent, 2-12 mm
diam x 1-2 mm thick, effused on wood, 5-50 mm long x 2-30 mm broad x 0.5
mm thick, with inconspicuous perithecial mounds; surface carbonaceous,
bay (6) when young, blackish when mature, long with a brown
tinge; dull yellow to pale orange granules beneath
surface, with KOH-extractable pigments dull green (70); the tissue below the
perithecial layer inconspicuous or up to 0.8 mm, blackish brown.
Perithecia spherical to obovoid, 400-500 µm diam x 500-750 µm
high, enclosed in a carbonaceous stromatal layer.
Ostioles papillate, conical, shiny black, encircled with a
convex truncatum-type disc 250-380 µm diam.
Asci 85-100 µm total length, the spore bearing-parts 58-75 µm
long x 3.5-4 µm broad, the stipes 25-40 µm long, with apical ring discoid,
inconspicuous, weakly amyloid or inamyloid, 0.5 µm high x 1 µm broad.
Ascospores light brown, ellipsoid-inequilateral, 6-8.2 x 2.8-3.4
µm (M = 7.3 x 3.1 µm), with straight germ slit spore-length on the
flattened side; perispore rarely dehiscent in 10% KOH, smooth.
Anamorph in nature: not observed. Anamorph in culture is Periconiella-like
(Ju & Rogers, 1996).
Habitat: on bark and wood of various hosts. Collected on
Acer negundo, Betula pendula, Castanea sativa, Quercus robur.
Known distribution: France, Russia.
Specimens examined: FRANCE, Pyrénées
Atlantiques (64): Osserain, Bel Air, 07 Nov. 2003, JF-03230,
on bark of Castanea sativa; Pau, Bois Bastard, 11 Jun. 1995, JF-95002,
on Castanea sativa; Oloron Ste Marie, bois de Larbaig, 26 Oct.
1998, JF-98147, on Quercus robur ; Auterrive, 05 Sept.
1999, JF-99199, on Acer Negundo. La Réunion
(974), Saint Philippe, Forêt Mare Longue, 20 Apr. 1999, FC-5285-1, leg. G.
Gilles, on unidentified wood (H. stygium).
Notes: Hypoxylon stygium var. annulatum
is a distinctive taxon,
characterized by the combination of the following features: black,
carbonaceous stromata, with papillate ostioles encircled with a disc, dull
green KOH-extractable pigments and
small-sized ascospores with the germ slit on the flattened side. This
last feature is unique among the known European species of
is another European taxon with ostiolar discs and
papillate ostioles, but its stromata are whitish and pruinose when young, KOH-extractable
pigments are yellowish, its perithecia are conspicuously exposed, with smaller ostiolar discs,
and its ascospores are larger (10-14.5 x 4.5-5.5 µm).
Hypoxylon stygium (Lev.) Sacc., the typical variety, is widespread in the
tropics. Ju and Rogers (1996)
erected the variety annulatum for
collections from Europe having larger perithecia and larger ostiolar discs
(250-380 µm diam versus 120-200 µm diam for the former). Comparison with a
collection of H. stygium (FC 5285-1) from La Réunion showed that in
the variety, not only the perithecia and the ostiolar discs are larger
but the ascospores also are slightly larger, apical rings are mostly inamyloid and
perispores mostly indehiscent. The results of HPLC analyses
(Quang et al., 2005)
support the close relationship between H.
stygium and its variety annulatum: both contain a BNT derivative
named daldinone A as prevailing metabolite, along with BNT, but H. stygium
differs in having large amounts of truncatone that is only present in its
variety annulatum as traces. Daldinone A is noteworthy in being present
as well in Daldinia concentrica
(Quang et al., 2002b), in two members
of the section Hypoxylon, i. e.,
H. intermedium and
H. hypomiltum. var lavandulocinereum
(Hellwig et al., 2004), and in
another member of the section Annulata, H. bovei var.microspora
(Quang et al., 2005)
Hypoxylon stygium var. annulatum
is not uncommon in the French departments Gironde, Landes
and Pyrénées Atlantiques, where temperature is usually
very mild in winter. It is noteworthy that, despite an active search, it
was not collected in Ariège where oceanic influence is less sensible and
winters are somewhat colder. Its distribution in Europe is poorly known
and should be completed by additional records that can be expected from