Description: Thallus crustose, endosubstratic and indistinct to thinly episubstratic and poorly developed, with a I- medulla. Apothecia cryptolecanorine to lecideine, adnate to sessile, black, 0.2-0.6(-0.75) mm across, with a flat to slightly convex, epruinose or slightly pruinose disc, and a thin proper margin. Proper exciple dark brown to brown-black, N-, Aethalea-type; epithecium brown; hymenium colourless, not inspersed; paraphyses 3-5.5 µm thick at apex; hypothecium dark brown. Asci 8-spored, Bacidia-type. Ascospores 1-septate, pale brown, ellipsoid, straight, 9-13 x (3.5-)4-4.5(-6.8) µm, Buellia-type, thin-walled and not constricted at septum, smooth, but often becoming microrugulate when overmature, with ontogeny of type A. Pycnidia black. Conidia bacilliform, straight, 2.5-4 x c. 1 µm. Photobiont chlorococcoid. Spot tests: thallus K- or K+ yellow turning to red, C-, KC-, P-. Chemistry: no lichen substances or norstictic acid in thallus.
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.