Description contributed by Graham Kinsey, CABI, based on Wehmeyer (1933).
Anamorph: Phomopsis sp. Conidiomata 300-700 µm diam. Alpha-conidia 11-15 x 2-2.5 µm; beta-conidia 8-13(-15) x 1-1.5(-2) µm.
Teleomorph: Stromata on the host surface as hemispherical to conical pustules 0.5-1 mm diam. with a central brown to black ectostromatic disc that is circular or fusoid and laterally elongate, ectostroma yellow-white to greyish, no blackened zones present in the substrate. Ascomata 350-750 x 350-500 µm, definitely clustered, ostioles hemispherical to short-cylindrical and collectively erumpent through the ectostromatic disc. Asci 58-70 x 8-10 µm, clavate. Ascospores 13.5-18.5 x 4-5.5 µm, fusiform-ellipsoidal, often inequilateral, with or without slight median constriction, 2- to 4-guttulate.
Wehmeyer considered this a doubtful species that merges with Allantaporthe decedens, which also occurs on Corylus, and as such it probably also belongs in Allantoporthe.