Description: Thallus crustose, inconspicuous, not discolouring the bark, not lichenized. Perithecia black, usually ellipsoid, with a flat border formed by the spreading involucrellum (0.3-)0.4-0.6 x 0.2-0.5 mm. Involucrellum dimidiate, brown in water, K+ greenish, of compacted hyphae and bark cells; exciple thin, usually colourless, surrounding the centrum; pseudoparaphyses slender, distantly branched, 1.5-2 μm thick, the cells 8-15(-18) μm long; downwardly projecting periphysoids present near the ostiole. Asci 8-spored, subcylindrical, fissitunicate, with two functional wall layers, 65-100 x 12-16(-20)μm. Ascospores 1-septate (a few old spores occasionally 3-septate), clavate with rounded apices, strongly constricted at septum, with often unequal cells, each cell often biguttulate but without a median constriction (except sometimes in the lower cell), (13-)15-23(-24) x 5.5-8(-9) μm; perispore distinct, c. 2 μm thick in K. Pycnidia black, not always present, 50-100 μm across. Conidia hyaline, thread-like, more or less straight, 7-11 x 0.8-1 μm. Photobiont absent. Spot tests: all negative. Chemistry: without lichen substances.
Note: a mainly temperate, perhaps holarctic early coloniser of smooth bark, found on twigs of deciduous trees, especially Carpinus and Corylus, but also on Quercus and Sorbus, facultatively, or most probably non-lichenised. For nomenclatural matters see Harris (1995).