Description contributed by Graham Kinsey, CABI.
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.
On dead stems of Arctium and possibly on other Asteraceae including Cirsium, Hypochaeris and Senecio.
England (Warwicks), E. Ireland (Wicklow, Louth), Scotland (Mid & North & South Ebudes, Shetland).