Thallus crustose, orbicular to irregularly spreading or in coalescing patches, to 20 cm diam., prothallus black, often conspicuous at margins and between areolae. Areolae contiguous to dispersed, to 2 mm diam., rarely rounded, ± angular, flat to convex, bright yellow to greenish-yellow, smooth, dull or glossy. Apothecia to 1.5 mm diam., between areolae, rounded to angular, flat, matt, rarely subconvex, margins thin, distinct or disappearing. Hypothecium dense, brown-black 100-300 µm tall. Hymenium 100-180 µm tall colourless or faint brownish. Asci 100-150 × 20-30 µm containing 8 spores. Ascospores muriform with few to many septa 20-40 × 10-22 µm. Chemistry: Medulla K-, C- or ± red, Pd+ yellow. Rhizocarpic acid (UV++ yellow), psoromic and often gyrophoric acids, rarely barbatic acid.