Trapelia obtegens (Th. Fr.) Hertel

    Thallus crustose, highly variable, made of areoles, more or less convex, brown-greenish, greyish, almost blackish, covered in places with soredia in small heaps, pale greenish, yellow-greenish, pale green-ochraceous. Apothecia  rare, in small number, scattered all over the thallus, 0.2-0.5 mm diam., disc brown-pink to dark brown, exciple thin, paler. Ascospores simple, ellipsoid, 11-15 x 4-7 µm. Photobiont: chlorococcoid. Thallus : C+ red, K-, Pd-. On siliceous rocks, stone walls, in dust and nutrient-rich areas.*