Description: Thallus crustose, episubstratic, whitish to pale grey, consisting of a few scattered areoles, usually delimited by a conspicuous, black, often fimbriate prothallus. Medulla white, I+ blue. Apothecia cryptolecanorine to zeorine, 0.3-0.4 mm across, black, immersed. Proper exciple poorly developed, aethalea-type, the inner hyphae narrow, hyaline, prosoplectenchymatous, the outer hyphae parallel, moderately swollen and usually strongly carbonized with brown and aeruginose pigments reacting N+ violet-red; epithecium brown to green, N+ violet-red; hymenium colourless, not inspersed with oil droplets, 60-80 μm high; hypothecium colourless to dark brown. Asci 8-spored, clavate to cylindrical-clavate, the apical dome K/I+ dark blue with a pale, conical-pointed apical cushion (axial mass), the wall I-, but the thin outer gel I+ blue, Bacidia-type. Ascospores 1-septate, slightly constricted at septum, brown, oblong-ellipsoid, 13-18 x 7-10 μm, Buellia-type, thin-walled throughout, with a microrugulate ornamentation. Photobiont chlorococcoid. Spot tests: thallus K- or K+ red (needle-like crystals), C-, KC-, P- or P+ faintly yellow, UV-. Chemistry: variable amounts of norstictic acid.
Note: on stones and low siliceous rocks near and above treeline; very closely related to B. leptolepis, based on a type from Northern Siberia and also reported from Carinthia (Austria), but perhaps much overlooked in the Alps; to be looked for in the Italian Alps.