Description: Thallus crustose, episubstratic, areolate, dark reddish brown, somehow shiny, forming 2-5 cm wide patches, sometimes delimited by a black prothallus. Areoles 0.2-0.8 mm wide, angular, slightly concave to flat, contiguous or dispersed over a black hypothallus, which gives the thallus a brown-black general colour. Medulla brown-black, I-; algal layer extending below the hypothecium. Apothecia cryptolecanorine-aspicilioid, immersed, 1-2 per areole, round to slightly irregular, 0.1-0.3(-0.4) mm across, with a black, dull, concave to slightly convex, epruinose disc, and a thin thalline margin which is level with disc. Proper exciple grey-brown in outer part, colourless within, up to 90 µm wide; epithecium blue-green to yellowish brown, 7-10 µm high, N+ red; hymenium colourless, 45-60 µm high, I+ blue; paraphyses strongly coherent, richly branched and anastomosing, c. 2 µm thick at base, the apical cells not or hardly swollen, up to 2.5-3 µm wide; hypothecium colourless or pale yellow-brown. Asci 8-spored, broadly clavate, very thin-walled, with a K/I+ blue, tall tholus penetrated by a faintly amyloid apical cushion, the wall K/I-, surrounded by a blue outer layer, Lecanora-type. Ascospores 1-celled, hyaline, ellipsoid, 7-14 x 3-6 µm, thin-walled, without a distinct epispore. Photobiont chlorococcoid. Spot tests: cortex K-, C-, KC-, P-; medulla P+ red. Chemistry: medulla with argopsin.
Note: on hard, steeply inclined surfaces of crystalline siliceous rocks, exceptionally on dolomite, near or above treeline; probably overlooked in the Alps, but certainly not common.