Description: Thallus crustose, episubstratic, rimose-areolate, covered in a chalk-white to white-grey pruina giving the thallus a farinose appearance, consisting of 0.8-2 mm wide and 1-3 mm thick, flat to convex, irregularly angular areoles. Apothecia lecanorine, semi-immersed in the thallus, 2-5 mm across, with an initially concave and urceolate, then flat, usually pruinose disc, and a thick thalline margin. Proper exciple blackish brown, up to 65 µm wide laterally, pseudoparenchymatous; epithecium poorly differentiated, colourless to brownish; hymenium colourless, 120-190 µm tall, non amyloid; paraphyses simple, flexuose, 1-2 µm thick, the apical cells not swollen; hypothecium colourless, c. 15 µm thick. Asci 4-spored, narrowly clavate to subcylindrical, the wall evenly thickened when mature, the somewhat abrupt apical thickening with a thin, internal apical beak, lacking any apical apparatus, the contents I+ orange-red, the walls I-, not fissitunicate. Ascospores muriform, with 4-7 transverse and 1-2 longitudinal septa, at first hyaline then turning brown, broadly ellipsoid, 25-40 x 10-17 µm,. Photobiont chlorococcoid. Spot tests: thallus K-, C+ red, KC- P-, UV- Chemistry: lecanoric acid.
Note: a widespread temperate to southern boreal-montane lichen found in rock fissures, on vertical or underhanging surfaces of calcareous rocks, often in woodlands, with a wide altitudinal range.