Rhizocarpon richardii  

Thallus to 8 cm diam., areolate, often in small patches that sometimes coalesce. Prothallus well-developed, black. Areoles to 0.5 mm diam., grey to brown, usually with a faintly grey-violet tinge, matt, contiguous, angular, ± flat; medulla I+ blue.
Anamorph: no information available.
Teleomorph: ascomata apothecia, to 1 mm diam., black, not pruinose, irregular in shape but usually ± orbicular, remaining flat or becoming weakly convex. True exciple indistinct but usually persistent, brown-black at the rim, pale brown to colourless in the inner part, containing crystals dissolving in K, K–. Epithecium dark olive-green to grey-black, containing crystals dissolving in K, K– or intensifying green. Hymenium colourless. Hypothecium dark, red-brown, K–. Ascospores 22-27 × 11-14 μm, mainly 1-septate, but secondary transverse or oblique septa may occur in one or both cells of the primary division, strongly constricted at the primary septum and sometimes even fragmenting, persistently colourless, only becoming faintly grey-brown with age, with a broad gelatinous sheath.
Chemistry: medulla C± red, K± yellow, Pd± orange (± gyrophoric, ± stictic and norstictic acids).