Description contributed by Graham Kinsey, CABI, derived from Wehmeyer (1933).
Anamorph: Phomopsis carpini (Sacc.) Höhn. (1906). Conidiomata 1-2 mm diam. Alpha-conidia 12 x 3-4 µm.
Teleomorph: Stromata seen on the host surface as numerous conic pustulate structures, 0.5-1.5 mm diam, often with wide angular ruptures of the periderm, entostroma pustulate-effuse, with a fine but definite dorsal zone which may run along the surface of the bark. Ascomata 320-480 x 320-400 µm, spherical or irregular from crowding, clustered in the pustulate entostromatic areas, ostioles stout-cylindrical and erumpent in compact clusters. Asci 55-65 x 6.5-9.5 µm, clavate. Ascospores (13-)15-17(-20) x 2.5-3.5(-4) µm, oblong-cylindrical, with rounded ends, 4-guttulate.