Description: Thallus crustose, endolithic to thinly epilithic, continuous to rimose or granular, white to pale brown. Apothecia lecideine, first often slightly immersed, then broadly sessile and constricted at base, (0.15-)0.2-0.4(-0.6) mm across, with a reddish to dark brown, rarely black, first flat but soon convex, usually epruinose disc, and a thin, slightly raised, entire, finally disappearing margin. Exciple pale to dark brown and K+ purple at outer edge, pale brown to colourless within, of conglutinate hyphae; epithecium pale to dark brown, K-, N-; hymenium colourless, I+ blue, then wine red; paraphyses simple, easily free, the tips capitate with dark brown pigment within the walls; hypothecium more or less colourless. Asci 8-spored, subcylindrical, the tholus I+ blue, the gelatinous coat I+ violet. Ascospores 1-septate, hyaline, oblong or oblong-ellipsoid, 7-10(-12) x (2-)2.5-3.5(-4) µm. Pycnidia globose-ovoid, the wall brown (cells with dark pigment caps). Conidia ellipsoid to short-cylindrical, 2-3.5 x 0.7-1.3 µm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-. Chemistry: no lichen substances in thallus.
Note: a mainly mild-temperate lichen found on limestone, more rarely on dolomite, sometimes on nutrient-enriched, base-rich siliceous rocks, with optimum in open woodlands but present also inside conurbations as well, and on monuments in archaeological areas, with a wide altitudinal range.