Hypoxylon submonticulosum Ju & Rogers.
Stromata irregularly effused to elongated, with inconspicuous
perithecial mounds, 8-60 mm
long x 4-20 mm broad x 0.6 mm thick; surface rust (39) to bay (6) when young,
blackish brown to black when mature, shiny; blackish carbonaceous tissue
beneath surface and between perithecia devoid of coloured granules,
without apparent KOH-extractable
pigments, but with pale livid violet (79) pigments from immature stromata
with a bay (6) surface; the tissue below the
perithecial layer blackish, up to 200 µm thick.
Perithecia obovoid, 250-320 µm diam x 380-450 µm high.
Ostioles higher than the stromatal surface, black, shiny,
Asci 115-135 µm long x 7.5-8 µm broad, the spore bearing-parts
65-73 µm long, the stipes 40-65 µm long, with apical ring discoid, weakly
amyloid, 1.5 µm high x 2.8 µm broad.
Ascospores brown, ellipsoid slightly inequilateral, 9.5-11.5 x
4-5.5 µm (M = 10.6 x 4.6 µm), with straight germ slit less than
spore-length; perispore indehiscent in 10% KOH.
Anamorph in nature not observed. Anamorph obtained in culture
(Ju & Rogers, 1996).
Habitat: on rotten decorticated wood, Ulmus sp., Populus sp.
Known distribution: Europe (France), North America (USA).
Specimen examined: FRANCE, Pyrénées Atlantiques
(64): Auterrive, banks of Gave d'Oloron, 05 Sept. 1999, FC 667, on a trunk of
Ulmus sp.; same location, 17 Nov. 2002, JF-02219, on Populus sp.;
same location, 17 Nov. 2002, JF-02220, on Ulmus sp.
Notes: Stromata of H. submonticulosum which are blackish, effused,
carbonaceous and with papillate ostioles, resemble members of
Nemania S. F. Gray, and for this reason may be easily overlooked,
unless they are found at young stage with their rust to bay coating on
stromatal surface and yielding livid violet pigments in 10% KOH. In
Nemania, young stromata may be covered with a whitish, greyish, greenish or
ochraceous velvety hyphal tissue, but are never rusty, and a whitish
soft tissue is frequently present between the perithecia. In addition,
their ascal apical ring is higher than broad (inverted hat-shaped), never
discoid as in Hypoxylon, and the germ slit is usually on the
flattened side of ascospores
Hypoxylon submonticulosum was previously known only from North
America and is reported for the first time from Europe. It differs from
its tropical counterpart H. monticulosum Mont. in having
slightly larger ascospores with a short straight germ slit and
perispore indehiscent in 10% KOH. HPLC analyses did not yet reveal whether
H. submonticulosum differs from H. monticulosum, in which BNT
is the compound responsible for the livid violet pigments obtained in KOH
(Hellwig et al., 2004).