Thallus areolate, up to 2 cm diam. or confluent; hypothallus usually well developed, black; areolae up to 0.4 mm diam., grayish brown to dark brown, dull, scattered to contiguous, round to angular, plane to weakly convex; medulla KI–. – Apothecia up to 0.7 mm diam., black, epruinose, orbicular, plane or weakly convex, with a persistent margin; excipulum brownish black, K–; hypothecium dark brown, K–; hymenium colourless; epihymenium olivaceous brown, K–; no crystals in the apothecium; ascospores 8 per ascus, eumuriform, persistently colourless, 29–40 × 11–18 µm. – Conidiomata not seen.
No lichen substances.
On siliceous and schistose rock, often irrigated rock faces or near brooks. Rarely collected.
The species differs from R. lavatum in having smaller apothecia and a darker, not ochraceous thallus. It differs from R. reductum in having darker, more plane areoles which lack stictic acid.