Thallus areolate, up to 10 cm diam.; hypothallus well developed, black; areolae up to 1 mm diam., medium gray to dark grey, sometimes with a brown tinge, dull, scattered to contiguous, orbicular to somewhat angular, weakly convex to hemispherical; medulla KI–. – Apothecia up to 1 mm diam., black, epruinose, more or less orbicular, plane to weakly convex, persistently marginate; excipulum brownish black in the rim, pale brown to colourless in the inner part, containing crystals dissolving in K, K+ yellow to red; hypothecium dark brown, K–; hymenium colourless or faintly green; epihymenium olivaceous green, not containing crystals, K– (turning brighter green); ascospores 1 or 2 (–4) per ascus, eumuriform, persistently colourless or becoming faintly green with age, 29–44 × 16–27 µm. – Conidiomata not seen.
Norstictic acid; spot tests: medulla PD+ yellow, K+ red, C–.
On siliceous rock, both in the lowlands and in the mountains.
The species resembles most closely R. subgeminatum, see that species for discussion. It may also be confused with R. geminatum, but that species contains stictic acid and forms ascospores that soon turn dark greenish brown.