Hypoxylon rubiginosum  

Anamorph: present at margins of young stromata or on old stromata, pale to yellow-brown, velvety. Conidiophores Nodulisporium-like, slightly roughened, yellowish to light brown. Conidiogenous cells 10-30 x 2-3 µm. Conidia ellipsoidal, 5-6 x 3-4 µm, yellowish.
Teleomorph: stromata effuse to effused-pulvinate, with inconspicuous to very conspicuous perithecial mounds, to 80 mm long x 30 mm broad, 1-1.5 (-2) mm thick; surface rust-coloured to dark brick-red, the margins yellow to dark orange and frequently widely effused when immature; orange brown granules present beneath surface and between perithecia, with KOH-extractable pigments orange; the tissue below the perithecial layer usually conspicuous, dark brown to blackish. Ascomata perithecia, spherical to obovoid, 300-650 µm diam x 450-800 µm high. Ostioles umbonate, lower than the stromatal surface, on mature stromata often surrounded by a white ring 50-70 µm diam. Asci 130-180 µm (total length) x 6-9 (-10) µm, the spore bearing-parts 56-95 µm long, the apical ring amyloid to weakly amyloid, discoid, 0.5-1.5 µm high x 2-2.7 µm diam. Ascospores brown to dark brown, ellipsoid-inequilateral, 9-11 (-12) x 4-5.5 µm, with an inconspicuous straight germ slit the length of the spore; outer layer (perispore) dehiscent in 10% KOH, smooth.

Description mostly adapted from http://pyrenomycetes.free.fr/index.htm