Description contributed by Graham Kinsey, CABI, based on Wehmeyer (1933).
Anamorph: Phomopsis petiolorum (Desm.) Grove (1917). Alpha-conidia 8-10 x 2-2.5 µm; beta-conidia 13-22 x 1-1.5 µm.
Teleomorph: stromata on the host surface as ± pustulate ruptures or perforations of the host periderm through which the ostioles are erumpent, entostroma strongly differentiated and of the colour of the wood, usually pustulate-effuse, but pustulate areas sometimes crowded.Ascomata 350-600 x 350-550 µm, in ± definite clusters within the pustulate areas, occasionally scattered irregularly, ostioles short and stout-cylindrical and erumpent in small loose clusters or somewhat larger irregular groups. Asci 60-80 x 6-9 µm, clavate, with a refractive apical ring. Ascospores 13-17(-25) x 3-4(-5) µm, narrowly fusiform-ellipsoidal, constricted at the septum.