Anisomeridium biforme (Borrer) R. C. Harris

    Thallus crustose, thin, smooth, but frequently crackled or fissured, whitish, dirty white or pale greyish, pale grey-green, (N.B. Sometimes on Fraxinus the thallus is olive green so wet and young.), delimited by a thin diffuse blackish prothallus. Perithecia usually numerous (but not always !), 0.3-0.5 mm diam., black, more or less immersed in thallus, leaving a small black cup when falling. Ascospores ellipsoid, uni-septate, 12-16 x 5-6 µm. Pycnidia numerous scattered all over the thallus or in small clusters possibly confused with perithecia;  of two types: 1) 0.1- 0.2 mm diam., black, more or less conical  with white gelly exudate on top (in the form of filaments or small twists), the gelly containing macroconidia; or 2) 0.05-0.1 mm diam., ± immersed, hemispherical to globose, black, designing dot lines and containing macroconidia. Photobiont : Trentepohlia. C-, K- ou K+/- greenish, KC-, Pd-. Common on smooth or rough bark of broad-leaved trees. May be confused with Acrocordia gemmata  whose perithecia are much bigger and pycnidia less numerous and devoided of black prothallus.