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Hypoxylon cercidicolum (Berk. & M.A. Curtis ex Peck)
Ju & Rogers.
Stromata discoid, erumpent from bark, 3-15 mm diam x 1-1.5 mm
thick, conspicuously encircled with a rounded stellate margin of fungal
tissue covering the ruptured and turned down cortical periderm, sometimes
coalescent, usually wrinkled between inconspicuous to conspicuous
perithecial mounds; surface dark brick (60) to sepia (63); orange to orange brown
granules beneath surface with KOH-extractable pigments orange (7) to sienna (8); the tissue
below the perithecial layer inconspicuous or up to 700 µm, dark brown.
Perithecia obovoid to infrequently tubular, 250-500 µm diam x
650-700 µm high.
Ostioles lower than the stromatal surface, surrounded by a
ring of white substance 90-120 µm diam.
Asci 140-175 µm total length x 8-9 µm broad, the spore
bearing-parts 60-93 µm long, the stipes 80-88 µm long, with apical ring
absent, inamyloid.
Ascospores brown to dark brown, ellipsoid-inequilateral, often
broadly crescent-shaped, 9.5-11.5 x 4.8-6.2 µm (M = 10.6 x 5.3 µm), with
faint straight germ slit spore-length; perispore dehiscent in 10% KOH,
smooth.
Anamorph in nature is Hadrotrichum pyrenaicum O. Petrini
& Candoussau (1983), growing on immature stromata, dark brick (60)
frequently with olivaceous (48) tinge, deeply wrinkled. Conidiogenous cells hyaline to light
brown, 10-15 x 3-4 µm; conidia ellipsoid, light olive brown, 6-7 x 4-5 µm.
Habitat: on bark of dying or dead branches of Fraxinus still
attached to the tree.
Known distribution: Central and southern Europe (Czech Republic,
France, Switzerland) and North America (Canada, USA).
Specimens examined: FRANCE, Ariège (09): Castelnau
Durban, Douach, 19 Feb. 1998, JF-98023, on Fraxinus excelsior;
Rimont, Las Muros, 30 Sept.1996, JF-96090, on Fraxinus
excelsior; Rimont, ruisseau de la Maille, 16 Jul. 1998, JF-98081,
on Fraxinus excelsior ; Rimont, Las Muros, 20 Oct. 2001,
JF0-1129, on Fraxinus excelsior.
Notes: Both immature stromata bearing the anamorph and fertile stromata
with ascigerous perithecia are highly distinctive among other Hypoxylon
taxa in being discoid and encircled with a swollen stellate margin
that forms on the surrounding ruptured cortical periderm. Nevertheless, if
immature stromata of H. cercidicolum are frequent in suitable
stations, mature stromata containing fertile perithecia occur much more
rarely and collecting them remains exceptional.
Hypoxylon cercidicolum grows on dying branches before they fall
down to the ground and is restricted to Fraxinus. It occurs in
shadowy and damp places and usually stops growing when branches are in
contact with the soil, as also do H.
intermedium (on Fraxinus) and H. laschii
(on Populus).
Microscopically, H. cercidicolum is characterized by lacking
ascal apical ring, a feature shared by H.
intermedium and H.
commutatum. They both mainly differ from H. cercidicolum in
having pulvinate to hemispherical stromata.
Hypoxylon cercidicolum was described as H. moravicum
Pouzar by
Pouzar (1972),
in a sense which fits perfectly the material
examined for this study, but
Ju and Rogers (1996) assessed it was
identical with Diatrype cercidicola Berk. & M.A. Curtis ex
Peck and its synonym H. suborbiculare Peck. In
order to avoid confusion of H. cercidicolum ss Ju & Rogers
with H. rubiginosum (Pers.: Fr.) Fr. var. cercidicola (Berk. & M.A.
Curtis ex Peck) Petrini
(Petrini & Müller, 1986) and H. cercidicola
ss. Granmo, the taxon represented by these two latter names
was now named
H. petriniae Stadler & Fournier
(Stadler et al., 2004b)
The results of HPLC analyses of H. cercidicolum
(Stadler et al., 2004b) show
it contains large amounts of mitorubrin, along with rubiginosin A and rubiginosin
C, and traces of mitorubrinol and orsellinic acid, while the type material of
H. suborbiculare shows only rubiginosin C and traces of mitorubrin
and orsellinic acid, and unknown compounds that are probably artefacts due to
preservative treatment. Both fungi are closely related but for the moment, HPLC
results are not conclusive enough to consider they are conspecific. Fresh collections
of H. cercidicolum from USA should allow for a better comparison.
Nevertheless, their lack of BNT provided evidence for the specific status of
H. petriniae
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