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Hypoxylon subticinense Ju & Rogers.
Stromata discoid to effused-pulvinate, frequently coalescent,
with inconspicuous to infrequently conspicuous perithecial mounds, 6-35 mm
diam x 1-1.6 mm thick; surface sienna (8), rust (39), powdery when young with a villose,
ochreous (44) to sienna (8) margin, becoming dark brick (60) to
sepia (63) when mature;
orange granules beneath surface and between perithecia,
with KOH-extractable pigments orange (7) to sienna (8); the tissue below the
perithecial layer blackish brown to black, 0.5-1.2 mm thick.
Perithecia obovoid to tubular, 200-300 µm diam x 400-580 µm
high.
Ostioles lower than or at the same level as the stromatal
surface, at the centre of a black discoid area 40-80 µm diam.
Asci 145-170 µm total length x 6-7.5 µm broad, the spore
bearing-parts 60-77 µm long, the stipes 80-96 µm long, with apical ring
discoid, amyloid, 1-1.2 µm high x 2-2.8 µm broad.
Ascospores brown, ellipsoid nearly equilateral, 8-11.5 x 4-5.5
µm (M = 9.7 x 4.7 µm), with straight germ slit spore-length; perispore
indehiscent in 10% KOH, smooth.
Anamorph in culture: ochreous (44), velvety, growing on
young stromata. The conidiogenous structure is Virgariella-like.
Conidiogenous cells yellowish to rusty, finely to coarsely roughened,16-47
x 2-4.8 µm; conidia ellipsoid, hyaline, 3.5-5.5 x 2.8-3.5 µm.
Chlamydospores globose to ellipsoid, coarsely incrusted, rusty, 4-6 µm
diam, originating from the wall of conidiophores and from incrusted hyphae
2.8-3.5 µm wide.
Habitat: on bark or decorticated wood of various hosts. Found
on rotting wood lying on the ground (Acer campestre, Baccharis
halimifolia, Hedera helix, Malus sylvestris, Fraxinus excelsior) or on dead branches
hanging above the soil level (Populus tremula, Quercus ilex) or on dying shrubs
(Rhamnus catharticus).
Known distribution: France (Ariège, Charente Maritime, Morbihan,
Pyrénées Atlantiques) and USA.
Specimens examined: FRANCE, Ariège (09): Rimont,
Las Muros, 30 Dec. 1996, JF-96184, on Populus tremula;
Rimont, Las Muros, ruisseau de Peyrau, 26 May 1997, JF-97075, on
Fraxinus excelsior; Rimont, Las Muros, ruisseau de Peyrau, 07
Nov. 1998, JF-98181, on Acer campestre; Rimont, Las Muros,
ruisseau de Peyrau, 08 Feb. 1999, JF-99036, on Rhamnus
catharticus; Rimont, Las Muros, ruisseau de Peyrau, 28 Jul.
2000, JF-00135, on Rhamnus catharticus; Rimont, Las Muros, 25
Sept. 2000, JF-00223, on Malus sylvestris. Charente Maritime
(17): Ile de Ré, Forêt du Lizay, Petit bec, 28 Apr. 2004, JF-04075, on Quercus
ilex. Morbihan (56): Guidel, Locmaria, 24 Oct. 2002, JF-02198,
on Hedera helix. Pyrénées Atlantiques (64): Anglet, Chiberta, Jun.
1993, FC-276, leg. FC and G. Gilles, on Baccharis hamilifolia.
Notes: Hypoxylon subticinense is strikingly similar to
H. ticinense
in stromatal colours and shape; moreover, it has similar
KOH-extractable pigments and similar small-sized perithecia seated on a
thick basal layer. It differs from
H. ticinense
in having larger and equilateral ascospores with perispore indehiscent
in KOH, in having ostioles at the centre of a black discoid area on mature
stromata and in some details of anamorphic morphology
(Ju & Rogers, 1996).
Ju and Rogers (1996)
describe the ostioles as sometimes higher than the
stromatal surface but we did not observe this feature in the specimens
we collected.
HPLC analyses reinforce the distinction of the two species, showing
that H. subticinense belongs to the rubiginosum chemotype,
characterized by large amounts of mitorubrins and derivatives associated to
orsellinic acid and specific azaphilones, while H.ticinense belongs to
the fragiforme chemotype lacking azaphilones
(Hellwig et al., 2004;
Stadler et al., 2004b).
Rubiginosins A and C present in H. subticinense are lacking in H.ticinense,
which, on the other hand, contains mitorubrinol acetate lacking in
H. subticinense.
Hypoxylon subticinense has been rarely recorded and its ecology
is poorly known. Although it may be found, as H.
ticinense, on rotten wood lying on the ground, its occurrence on
standing dying shrubs or on dead branches that are not in contact with the
soil, providing that the air is humid enough, is noteworthy and may be
useful in distinguishing it in the field from H.
ticinense.
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