Description: Thallus crustose, episubstratic, areolate, brown, up to c. 0.5 mm thick, forming large patches to more than 10 cm in diam., wihout a distinct prothallus. Areoles angular, subconcave to slightly convex (mostly flat), 0.2-0.6(-1) mm wide, brown with usually whitish to pale grey margins, the peripheral ones often somehow elongate. Cortex 40-65 µm thick, overlain with an up to 70 µm thick epinecral layer; medulla white, with mostly vertically arranged hyphae, I+ violet-blue. Apothecia aspicilioid, immersed in the areoles, 0.3-0.6(-0.8) mm across, round to irregularly angular, mostly in dense clusters, with a subconcave to flat, brown to black-brown, matt, epruinose disc, and a whitish to dark grey, finally sometimes slightly prominent margin. Exciple 50-110 µm wide, dark green in outer part, colourless within; epithecium brown to olive-brown; hymenium colourless, 60-95 µm high, I+ blue; paraphyses branched and anastomosing, 2-3 µm thick in lower part, the apical cells up to 4 µm wide; hypothecium colourless, c. 30 µm high. Asci 8-spored, with a distinct tholus, an internal I+ blue cap, and I+ violet-blue lateral parts, without an amyloid tube-structure, approaching the Rimularia-type. Ascospores 1-celled, hyaline, ellipsoid, (8-)9.5-13(-16) x 4.5-7.5 µm, halonate, the inner layer of the epispore I+ blue. Pycnidia black, immersed. Conidia bacilliform, 5-7 µm long. Photobiont chlorococcoid. Spot tests: K-, C-, KC-, P-. Chemistry: 5-O-methylhiascic acid.
Note: on vertical to overhanging faces of gneissic rocks above treeline; perhaps more widespread in the Alps, but not common.