Hypoxylon crocopeplum Berk. & Curtis.
Stroma effused to more rarely pulvinate, 4-50 mm long x 3-20 mm broad x
0.9-1 mm thick, irregularly elongate, with inconspicuous
perithecial mounds and a yellow effused margin while immature;
surface at first pale fulvous (43), apricot (42), sienna (8), eventually
dull bay (6) to sepia (63) with a greyish tone due to a whitish film; rust (39) to scarlet (5) granules
beneath surface and between perithecia with KOH-extractable pigments rust (39)
to bay (6); the tissue below the
perithecial layer blackish, up to 0.2 mm thick.
Perithecia obovoid to slightly tubular, more rounded at the periphery
of the stroma, 0.25-0.35
mm diam x 0.45-0.6 mm high. An underlying layer of old empty perithecia can
be observed in some stromata.
Ostioles umbilicate, surrounded by greyish discs 100-120 µm diam when
immature, appearing as black dots contrasting with the stromatal surface in mature stromata.
Asci cylindrical, originating from ascogenous hyphae, 170-190 µm total
length, the spore-bearing parts 75-95 µm long
x 9-12 µm broad, the stipes 80-110 µm long, with apical ring discoid, amyloid,
1.2-1.8 µm high x 2.4-3 µm broad.
Ascospores brown, ellipsoid-inequilateral with narrowly rounded ends, 11.4-14.4 x 6-7.2
µm, M = 12.6 x 6.5 µm (n=30), with a conspicuously sigmoid germ slit spore-length, uniseriate in
the ascus; perispore dehiscent in 10 % KOH, smooth.
Anamorph in nature: a Virgariella-like conidiogenous structure was observed
in culture on YMG (Stadler, unpublished data) and on JF-03233.
Habitat: so far recorded in France on Fraxinus and Ulmus, on bark
or on rotten decorticated wood of trunks lying on river banks.
Known distribution: pantropical and eastern North America
(Ju & Rogers, 1996), Europe (present study).
Specimens examined: FRANCE. Haute Garonne (31): Martres-Tolosane,
Le Moulin, 13 Dec. 2003, JF-03233, on a rotten trunk of Ulmus sp. (immature).
Loiret (41): Saint Georges du Cher, Camping, 16 Nov. 2003, on
Fraxinus excelsior, leg Paul Leroy (immature). Pyrénées Atlantiques
(64): Auterrive, île du Gave d'Oloron, 06 Nov. 2003, JF-03223,
on a rotten trunk of Ulmus sp.(mostly immature); same location and same
date, JF-03224, on bark of Fraxinus excelsior (mostly immature);
same location, 30 Jun. 2004, JF-04101, on bark of Fraxinus excelsior,
leg. JF and M. Stadler,
Notes: Hypoxylon crocopeplum primarily is a tropical species
which was so far unknown from Europe. The above findings might give the illusion
it is a recent invader, but it more likely has been overlooked as, in the field, it
is much like H. rubiginosum
and its numerous allies. However its immature
stromata are of a peculiar tone of orange which is different from other related
species in Europe and should have been noticed by field mycologists. Aside this
striking colour, immature stromata are distinctive in that their ostioles are
as a rule at the centre of a grayish disc, a feature not reported by
Ju & Rogers (1996)
for the specimens they examined. Mature stromata become dull
brown but remain noticeable on account of their black ostioles. The whitish
film present on the surface of some mature stromata was also reported by
Ju & Rogers (1996). The salient
microscopic features of this species are the rather broad ascospores with narrowly rounded
ends and their conspicuously sigmoid germ slit. Such a sigmoid germ slit is
known only from H. fuscum
among European species of Hypoxylon.
Hypoxylon crocopeplum is said to have a typical form in eastern North
America with thin stromata and obovoid perithecia, while the tropical form displays
thicker stromata with a thick basal layer and tubular perithecia
(Ju & Rogers, 1996).
Our collections are morphologically referrable to the North American
form. During his investigations on chemotaxonomy of Xylariaceae by the means
of HPLC, Dr. Marc Stadler obtained the secondary metabolite profile of H.
crocopeplum from the type collection at Kew. The HPLC profile of the collection
JF-03223 proved to be identical to that of the type material (unpublished data).
Regarding its secondary metabolites, H. crocopeplum is allied to the rubiginosum
group in containig mitorubrin, rubiginosin A and orsellinic acid, but contains
mitorubrinol which is lacking in H. rubiginosum
(Hellwig et al., 2004;
Quang et al., 2004).