Hypoxylon cohaerens (Pers.: Fr.) Fr. var. microsporum Rogers &
Stromata pulvinate, constricted at base, often coalescent, with
inconspicuous perithecial mounds, 2-15 mm diam x 1.5-5 mm thick; surface dark brick
sepia (63), becoming blackish ; dark orange brown granules
beneath surface, with KOH-extractable pigments varying from livid red
(56) to bay (6) or purplish grey (128); the tissue below the perithecia
brown to blackish brown, up to 4 mm thick.
Perithecia obovoid, 400-500 µm diam x 500-750 µm high,
discretely surrounded by a carbonaceous stromatal layer.
Ostioles papillate, black, at times at the centre of a discoid
depression 120-150 µm diam.
Asci 130-170 µm total length x 4-5.5 µm broad, the spore
bearing-parts 48-73 µm long, the stipes 75-115 µm long, with apical ring
inamyloid, 1.5 µm high x 2 µm broad.
Ascospores light brown to brown, ellipsoid-inequilateral,
6.8-8.8 x 3.4-4 µm ( M = 7.3 x 3.8 µm), with faint germ slit less than
spore-length; perispore dehiscent in 10% KOH, smooth, with a thickening on
the more convex side.
Anamorph in nature: dark rosy vinaceous (58) on young stromata or
at margins, turning livid purple (81) in 10% KOH. Conidiogenous cells 15-30 x 3 µm;
conidia ellipsoid, 3.5-4.8 x 2.5-2.8 µm. The conidiogenous structure is
Habitat : primary saprophyte on bark of fallen or cut off
branches or trunks of Quercus and Castanea in Europe; also
reported on Erica arborea and Laurus azorica in Portugal; a wider host range is
encountered in tropics.
Known distribution: Europe (southern England, France, Portugal,
Spain) and tropics (Colombia, Honduras, India, Mexico, Taiwan).
Specimens examined: FRANCE, Ariège (09): Ganac,
ruisseau de Ganac, 02 Jul. 2000, JF- 00111, on Castanea
sativa ; Montseron, Ouzeich, 20 Dec. 1996, JF-96181, on
Castanea sativa; Rimont, Las Muros, 19 Jan. 2001, JF-01006, on
Quercus robur; Charente Maritime (17): Ile de Ré,
St. Martin en Ré, Les Sallières, 28 Apr. 2004, JF-04065, on bark of Quercus
ilex. Haute Garonne (31): Saleich,
Artihaguère, 10 Feb. 2000, JF- 00009, on Quercus robur;
Landes (40): Capbreton, 06 Jun. 1982, FC-5252-82, on
Quercus suber. PORTUGAL: Ilha de Madeira, Levada
da Sawa de Faial (790 m), 23 Apr. 2004, leg. W. Jäger, det. M. Stadler, STMA
04W19, on bark of Laurus azorica.
Notes: In all collections examined, ascal apical rings were
inamyloid, while Ju & Rogers (1996) describe the ascal apical rings as
being occasionally amyloid. Hypoxylon cohaerens var. microsporum mainly differs
from the type in smaller ascospores having a faint shorter germ slit and
in vinaceous KOH-extractable pigments. Although it is reported to have a
wide host range in tropics (Ju & Rogers, 1996), Hypoxylon cohaerens
var. microsporum seems restricted to Quercus and Castanea
in our collecting area, while H. cohaerens
is restricted to Fagus and to northern hemisphere.
It may be easily confused in the field with H.
multiforme, which differs in having more conspicuous perithecial
mounds, sienna (8) to olivaceous (48) KOH-extractable pigments, amyloid ascal apical rings
and larger ascospores. Moreover, H.
multiforme is found mainly on Alnus,Betula and
Corylus, and hiterto has never been reported from Quercus or
When host is unknown, identification of H. cohaerens var.
microsporum relies on the combination of the following characters:
stromata pulvinate, restricted at base, with papillate ostioles, vinaceous
KOH-extractable pigments and ascospores averaging less than 8 µm long with
a short faint germ slit.
In a recent account on the chemotaxonomy of some members of Hypoxylon
section Annulata, Quang et al. (2005) reported
that, besides BNT, H. cohaerens contains specific azaphilones cohaerins A and B
which lack in the variety microsporum, HPLC profile of which appears
closer to that of H. multiforme. Awaiting further investigations on the secondary
metabolites of these latter taxa which probably are azaphilones close to cohaerins
A and B, Quang et al. (2005) demonstrated that
collections of H. cohaerens var. microsporum from Colombia,
France, Portugal and Taiwan all had identical metabolite profiles, confirming
that it was a single species with a wide distribution.