Entostroma normally widely effuse and indefinitely outlined, the host surface heavily blackened over wide areas, or slightly, irregularly or heavily blackened over widely effuse or confluent areas.
Anamorph: Phomopsis arctii (Sacc.) Traverso (1906). Conidiophores 25 x 1.5 µm. Alpha-conidia 6-10 x 2-3.5 µm; beta-conidia 18-25(-34) x 1-1.5 µm.
Teleomorph: ascomata 280-480 x 160-320 µm, globose to somewhat flattened, scattered singly in the host tissues or crowded and tending to be clustered in small groups. Asci (40-)47-60 x 7-10 µm, clavate, with a refractive apical ring. Ascospores 11-15(-17) x 2.5-3.5(-4) µm, fusiform-ellipsoidal, straight to slightly curved, often tardily septate, constricted at the septum when mature.
The above description is of Wehmeyer's host-restricted typical form on Arctium. The 'arctii' group occurs on a wide range of herbaceous plants and contrasts with the 'eres' group on woody plants.