Description: Thallus crustose, endosubstratic or rarely thinly episubstratic, white, pale grey or pale ochre-coloured, usually poorly evident. Apothecia lecideine, 0.3-0.8(-1.2) mm across, half to three quarters immersed in shallow pits in the rock, with a black (purple black when wet), epruinose, flat to slightly convex disc, and a thin, black (also when wet), slightly raised, usually persistent proper margin. Proper exciple thin, poorly developed, reddish brown in outer part, colourless to rarely pale brown within, of radially arranged hyphae, 20-85 µm thick laterally; epithecium ochre-brown to red-brown; hymenium colourless, 90-150 µm high, I+ partly pale blue; paraphyses sparingly branched and anastomosing, septate but not moniliform, 4-6 µm thick at mid-level, scarcely or not swollen at apex; hypothecium colourless to pale ochraceous brown, I-. Asci 8-spored, cylindrical-clavate, with a K/I+ blue outer layer and apical dome, and a central, K/I+ darker blue tube, Porpidia-type. Ascospores 1-celled, hyaline, ellipsoid to pear-shaped, (15-)16-23(-28) x 6-10(-12) µm, often guttulate, with a > 1 µm thick, gelatinous perispore when young, the wall of old spores not warted. Pycnidia black, laminal, isolated or clustered, partially immersed. Conidia bacilliform 4-5 x 1-1.5 µm, with apical and lateral conidiogenesis. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a mainly temperate, holarctic early coloniser of small calcareous pebbles in dry grasslands, widespread and locally common throughout Italy, especially below the montane belt.