Thallus crustose, spreading, 2-10 cm diam., prothallus conspicuous. Areolae close together, widely dispersed, usually separated by black strips of prothallus, some specimens with a distinct border formed of young areolae of characteristic shape, 0.3-2.5 mm diam., angular, concave to plane to convex, or rounded- angular to rounded and convex, yellowish-white to yellow to greenish-yellow, surface smooth, matt or glossy or scabrid. Apothecia 0.6-2 mm diam., round to angular, usually higher than surrounding areolae, plane to subconvex, with a distinct persistent margin, surface matt, minutely papillate, "sooty". Hymenium 70-100 µm tall, colourless to brownish, dark reddish or greenish in upper parts. Asci clavate, 60-80 × 15 µm. Hypothecium brown, 60-150 mm tall. Ascospores 8 per ascus, 1-septate, small, 11-18 × 6-8 µm. Chemistry: Medulla K+ red, Pd+ yellow, or K+ yellow and Pd+ brick red (rarely K-, Pd-). Rhizocarpic, stictic or norstictic acids, rarely psoromic acid.