Description: Thallus crustose, of variable thickness, endo- to episubstratic, continuous to rimose-areolate, whitish to grey; cortex overlain with a thin epinecral layer inspersed with crystals; medulla strongly amyloid, I+ violet. Apothecia lecideine, black, 0.5-1.2 mm across, sessile and constricted at base, with a flat to convex disc, and a thick, prominent, persistent proper margin. Proper exciple c. 100 µm wide, leptocline-type, homogeneously dark brown, with an additional orange pigment reacting K+ reddish (solution), the inner part of long-celled, interwoven hyphae, the outer part of long-celled, parallel, strongly agglutinated and thick-walled hyphae; epithecium brown; hymenium colourless, not inspersed with oil droplets, c. 75 µm high; hypothecium dark brown. Asci 8-spored, clavate, Bacidia-type. Ascospores 1-septate, brown, oblong, not constricted at septum, 12-16(-18) x (6-)7.5-8.5(-11) µm, Physconia-type, with a rugulate wall (but smooth-walled when young). Pycnidia black, immersed in thallus. Conidia bacilliform, 4-5 x c. 1 µm. Photobiont chlorococcoid. Spot tests: thallus K+ yellow, C-, KC-, P- or P+ very faintly yellow. Chemistry: atranorin.
Note: a mainly boreal-montane species found on steeply inclined to underhanging surfaces of hard siliceous rocks in upland areas. Earlier records (Nimis 1993: 140) from central and southern Italy, plus that from Sicilia by Grillo (1998) could refer to other related species (B. halonia, B. sardiniensis, B. saxorum, B. sejuncta and B. subdisciformis), and are not reported here.