Description contributed by Graham Kinsey, CABI, based on Wehmeyer (1933).
Anamorph: Phomopsis achilleae (Sacc.) Höhn. (1906). Alpha-conidia 8-10 x 2.5-4 µm; beta-conidia 26 x 1 µm.
Teleomorph: stromata with dorsal zone usually present as a blackening of the host surface but largely obscured by the overlying epidermis and appearing only as a slight discoloration of the surface, ventral zone absent. Ascomata ± seriately crowded or occasionally clustered, usually just beneath the surface and often forming small pustulate swellings on the surface. Ascospores 11-15(-17) x 2.5-4 µm.
Wehmeyer considered this to belong within the D. arctii aggregate.