Thallus crustose, thin to moderately thick, to 1.5 mm thick, white, sooty white, sometimes stained from substratum, areolate from smooth to bullate in thick material; no hypothallus. Apothecia to 2 mm broad, adnate or between the areolae, black, with prominent margin; exciple black or brown-black often with narrow clear edge; hypothecium 100 μm, light ochre to dark brown but paler than the sharply distinguished exciple; epihymenium green-black to brown-black, occasionally with light dead overlayer; hymenium 80-120 μm; subhymenium 30-60 μm, pale; paraphyses 2 μm, tips to 3.5 μm, anastomosing; asci clavate; spores ellipsoid or asymmetric, thin-walled, halonate when young, 15-25 x 7-16 μm.

Reactions: medulla 1+ blue, C—, K—, KC-,P-.

This species grows on calcium-bearing rocks. It is a circumpolar arctic and alpine species. In the West it is known from Colorado, Montana, Utah, and Alberta. It is also found in eastern Greenland.