Thallus cracked to areolate, often thin and sometimes partly endolithic; hypothallus indistinct; areolae up to 0.2 mm diam., pale brown, sometimes with a grey tinge, dull, more or less angular, smooth; medulla KI–. – Apothecia up to 0.4 mm diam., brownish black to black, epruinose, orbicular, persistently plane and distinctly marginate; excipulum olivaceous brown or greenish black, K–; hypothecium pure brown or partly olivaceous brown, K–; hymenium colourless; epihymenium medium brown, containing crystals dissolving in K, K–; ascospores 8 per ascus, 3-septate to submuriform, persistently colourless, 15–21 × 8–11 µm. – Conidiomata not seen.
Stictic acid; spot tests: medulla PD+ orange, K+ yellow, C–.
On schistose rock in the alpine region.
A rarely collected, poorly understood species. It was included in R. reductum by Feuerer (1991), but seems to differ in the poorly developed thallus which contains stictic acid, the thin margin of the apothecia, and the smaller ascospores.