Hypoxylon submonticulosum









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 m thick.

Perithecia obovoid, 250-320 m diam x 380-450 m high.

Ostioles higher than the stromatal surface, black, shiny, minutely papillate.

Asci 115-135 m long x 7.5-8 m broad, the spore bearing-parts 65-73 m long, the stipes 40-65 m long, with apical ring discoid, weakly amyloid, 1.5 m high x 2.8 m broad.

Ascospores brown, ellipsoid slightly inequilateral, 9.5-11.5 x 4-5.5 m (M = 10.6 x 4.6 m), with straight germ slit less than spore-length; perispore indehiscent in 10% KOH.

Anamorph in nature not observed. Anamorph obtained in culture is Virgariella-like (Ju & Rogers, 1996).

Habitat: on rotten decorticated wood, Ulmus sp., Populus sp.

Known distribution: Europe (France), North America (USA).

Specimen examined: FRANCE, Pyrnes 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).