Description: Thallus crustose, endosubstratic and indistinct to thinly episubstratic and poorly developed. Medulla I-. Apothecia cryptolecanorine to lecideine, sessile and constricted at base, black, 0.2-0.6(-0.75) mm across, with a flat to slightly convex, epruinose or often slightly pruinose disc, and a thin, raised, usually persistent proper margin. Proper exciple thin, aethalea-type, the inner hyphae hyaline, prosoplectenchymatous, the outer hyphae parallel and usually strongly brown-pigmented, N-; epithecium brown, N-; hymenium colourless, not inspersed with oil droplets; paraphyses 3-5.5 µm thick at apex; hypothecium dark brown. Asci 8-spored, clavate, Bacidia-type. Ascospores 1-septate, not constricted at septum, pale brown, ellipsoid, straight, 9-13 x (3.5-)4-4.5(-5.5) µm, Buellia-type, thin-walled throughout, the wall smooth, but often becoming microrugulate when overmature. Pycnidia black, immersed. Conidia bacilliform, straight, 2.5-4 x c. 1 µm. Photobiont chlorococcoid. Spot tests: thallus K- or K+ yellow turning red, C-, KC-, P- or P+ yellow-orange. Chemistry: without lichen substances or with norstictic acid.
Note: a much misunderstood silicicolous species, in the past frequently confused with B. sequax (Giralt & al. 2011). The Italian sample, collected by Buschardt and identified by H. Sipman, was collected in Vinschgau - Val Venosta, on south-facing rocky slopes NE of Tartsch, at c. 1200 m.