Thallus continuous to cracked, up to 1 cm diam. or several thalli confluent, pure white, pruinose, dull; hypothallus indistinct; medulla KI–. – Apothecia up to 1 mm diam., black, with a pruinose margin and a usually epruinose disc, orbicular, remaining more or less plane and marginate; excipulum dark brown in the rim, inner part paler brown, containing crystals dissolving in K, pigment K+ red, crystals K+ yellow; hypothecium brown, K–; hymenium colourless to pale brown, containing crystals at least partly dissolving in K; epihymenium reddish brown, K+ red; ascospores 8 per ascus, 1-septate, long remaining colourless, usually becoming unevenly green or brown with age, 12–16 × 6–10 µm. – Conidiomata not seen.
Stictic acid in the apothecia, apparently no lichen substances in the thallus; spot tests: PD–, K–, C– (thallus).
On calciferous rock; in South Norway in the mountains, in North Norway also in the lowlands. Rarely collected.
Resembles a small R. umbilicatum, but that species differs in having an olivaceous brown, K– epihymenium and larger, eumuriform ascospores. See also the rarely collected species R. caeruleoalbum, R. expallescens and R. glaucescens.