Description contributed by Graham Kinsey, CABI, based on Wehmeyer (1933).
Anamorph: Phomopsis oblonga (Desm.) Traverso (1906). Alpha-conidia 6-9 x 2-3 µm; beta-conidia 15-18 x 1 µm.
Teleomorph: stromata on host surface as numerous minute pustules or angular ruptures, through which the ostioles are erumpent singly or in small groups. Ascomata 240-800 x 160-500 µm, spherical or flattened, scattered singly, irregularly crowded or loosely grouped, not definitely orientated beneath the ectostromata but often erumpent through it, buried in either the wood or the bark. Asci 40-60 x 5-8 µm, clavate, with a refractive apical ring. Ascospores 9.5-14(-15) x 2.5-4 µm, fusiform, constricted at the septum.
The above description is of Wehmeyer's host-restricted typical form on Ulmus. This is the biggest species aggregate within the genus and is reported from a wide range of mainly woody plants.