Hypoxylon intermedium (Schwein.: Fr.) Ju & Rogers.
Stromata hemispherical, narrowly connected to the substrate at
the centre, rarely coalescent, with inconspicuous perithecial mounds, 2-7
mm diam x 1-3 mm thick; surface greyish sepia (106) to dark brick (60); pale
orange granules beneath surface, with KOH-extractable pigments
greenish yellow (16); the tissue below the perithecial layer light grey to grey
brown, 1-2.5 mm thick, extending upwards between the perithecia.
Perithecia spherical to obovoid, 250-320 µm diam x 400-600 µm
high.
Ostioles lower than the stromatal surface, on mature stromata
conspicuously encircled with a prominent ring of white substance 150-200
µm diam.
Asci 180-230 µm total length x 12-18 µm broad, the spore
bearing-parts 100-128 µm long, the stipes 85-110 µm long, with apical ring
lacking or highly reduced, inamyloid.
Ascospores dark brown to blackish brown,
ellipsoid-inequilateral, 16-23 x 8.2-10.8 µm ( M = 19.1 x 9.4 µm), with
straight germ slit spore-length; perispore dehiscent in 10% KOH, smooth.
Anamorph in nature: not observed.
Habitat: primary saprophyte on bark of dead branches of
Fraxinus excelsior before their fall on to the ground.
Known distribution: reported on Fraxinus sp. from Europe
and North America.
Specimens examined: FRANCE, Ariège (09): Orlu,
Réserve nationale d'Orlu, Jasse de Justiniac, 29 Jul. 2001, JF- 01155, on
Fraxinus excelsior; Rimont, Las Muros, 09 Sept. 2000,
JF-00198, on Fraxinus excelsior; Rimont, Las Muros, 04 Feb.
2001, JF-01011, on Fraxinus excelsior.
Notes: Hypoxylon intermedium, previously known as H.
fraxinophilum Pouzar, is highly distinctive in its stromatal,
microscopic and ecological features. It will be identified in the field
thanks to its hemispherical greyish sepia stromata with conspicuous
white substance surrounding the ostioles, growing on fallen dead branches
of Fraxinus found after a gust of wind or a tempest. It is
noteworthy that H. intermedium stops growing if branches are in
contact with the soil but is able to keep on growing during the following
season if branches remain hanging above the soil level. Contact with the
soil involves more humidity in the substrate and apparently favours more
competitive ascomycetes or basidiomycetes.
Field identification will be readily confirmed by the observation of
the following characters: KOH-extractable pigments greenish
yellow, large blackish brown ascospores and apical rings lacking.
Secondary metabolites of H. intermedium are hypomiltin and derivatives,
along with orsellinic acid (Hellwig et al., 2004).
Hypomiltin is a new azaphilone which is also the prevailing compound in
H. perforatum
and other tropical species such as H. hypomiltum and H. trugodes which,
however, are morphologically much different. This is an interesting and rather
unusual case of noncorrelation between morphology and metabolites profiles.
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