Distribution: C - Tosc, Sar (Scheidegger 1993). S - Si.
Description: Thallus crustiose, episubstratic, thin to thick, rimose to areolate or bullate, white, forming patches to more than 5 cm in diam. Medulla white, amyloid, 1+ violet. Apothecia lecideine, black, 0.4-0.8 mm across, sessile and constricted at base, with a flat to convex, epruinose disc, and a thick, prominent proper margin. Proper exciple leptocline-type, brown throughout; epithecium brown; hymenium colourless c. 100 µm high, not inspersed with oil droplets; hypothecium dark reddish brown. Asci 8-spored, clavate, Bacidia-type. Ascospores 1-septate, constricted at septum, brown, oblong, 13-15 x 6-7 µm, Physconia-type, with a microrugulate ornamentation. Pycnidia black, immersed. Conidia bacilliform, 6-5-8 µm long. Photobiont chlorococcoid. Spot tests: K+ yellow turning red, C- or C+ fleeting pink, KC- or KC+ fleeting pink, P- or P+ yellow. Chemistry: atranorin, gyrophoric, norstictic and connorstictic acids.
Note: a mainly Mediterranean lichen found on hard siliceous rocks in warm-dry, but rather shaded situations (e.g. on north-facing surfaces), both in maritime and inland habitats; related to B. saxorum, but with a different chemistry.