Thallus rimose to areolate, up to 2 cm diam.; hypothallus poorly developed, black; areolae up to 0.4 mm diam., medium brown to greyish, dull, mainly contiguous, angular, plane to weakly convex; medulla KI–. – Apothecia up to 0.5 mm diam., black, epruinose, mainly orbicular or often slightly angular, remaining plane, with a narrow and persistent margin; excipulum brownish black throughout or paler brown in inner part, lacking crystals, K–; hypothecium dark brown, K–; hymenium colourless; epihymenium green, not containing crystals, K–; paraphyses with a sharply delimited, dark brown pigment cap in the apical cell; ascospores 8 per ascus, 1-septate, persistently colourless, 15–19 × 7–10 µm. – Conidiomata not seen.
No lichen substances or rarely stictic acid; spot tests: medulla PD– and K–, or rarely PD+ orange and K+ yellow, C–.
Very rarely collected in western and northern Norway.
The species differs from R. hochstetteri mainly in having smaller ascospores.