Description: Thallus crustose, episubstratic, grey, areolate, up to 5 cm diam, the areoles flat to subconvex, 0.4-1 mm diam., developing on an often poorly evident black hypothallus. Medulla white, I-. Apothecia 0.6-1.2 mm across, aspicilioid when young, later lecideoid and semi-immersed at edges of areoles, mostly polygonal in outline, with a black disc and a thin margin, Proper exciple externally dark olive-brown at least in upper part, hyaline to brownish in inner part, inspersed with granules; epithecium olive-brown; hymenium colourless, 50-70 µm high, I+ blue; paraphyses mostly simple, 1.5.-2 µm thick at mid-level, the apical cells slightly enlarged, up to 4 mm wide, embedded in a pigmented gel; hypothecium colourless. Asci 8-spored, broadly cylindrical to subclavate, more or less of the Lecanora-type, but with a weakly defined apical cushion and ocular chamber. Ascospores 1-celled, hyaline, ellipsoid, 9-13 x 4-5 µm. Pycnidia black, immersed. Conidia thread-like, curved, 18-25 x c. 1 µm. Photobiont chlorococcoid. Spot tests: cortex K-, C-, KC-, P-; medulla K-, C-, KC-, P+ orange-red. Chemistry: protocetraric acid and miriquidic acids.
Note: an alpine to subnival species, confined to steep or overhanging surfaces of hard siliceous rocks, often with a high iron content.