Thallus areolate, up to 15 cm diam.; hypothallus well developed, black; areolae up to 1 (–1.5) mm diam., greyish yellow or greenish yellow, dull to slightly shiny, contiguous to scattered, irregular to orbicular or angular, plane to strongly convex, smooth; medulla KI+ dark violet.. – Apothecia up to 1 mm diam., black, epruinose, angular to orbicular, plane to concave or slightly convex, usually persistently marginate; excipulum with a dark brown rim and a paler brown inner part, K+ red; hypothecium dark brown, K–; hymenium colourless or faintly green; epihymenium green or brown, K– or K+ red; no crystals or granules in the apothecia; ascospores 8 per ascus, eumuriform, dark brown, 30–50 × 12–22 µm. – Conidiomata not seen.
Four chemical strains are known from Norway, containing rhizocarpic acid and 1) barbatic acid, 2) psoromic acid, 3) stictic acid, or 4) no additional lichen substance; spot tests: medulla PD– or PD+ yellow/orange, K– or K+ yellow, C–.
On open rock, especially at sites exposed to dust impregnation. In the lowlands, rarely collected.
This poorly understood species differs from R. geographicum mainly in having larger ascospores. The other large-spored, yellow species, R. saananse, differs in forming larger, more bright yellow, often pruinose areoles and often pruinose hypothallus.