Description: Thallus crustose, fully endosubstratic, usually covering large surfaces, pale pink-purple. Cortex (lithocortex) densely prosoplectenchymatous, of conglutinated hyphae intermingled with microcrystals, the upper cells pink-violet; algal layer discontinuous, the photobiont cells in clusters; medulla prosoplectenchymatous. Perithecia black, usually numerous, completely immersed in thallus and leaving deep pits in the rocks when they fall off, the apex slightly projecting to flattened. Involucrellum narrower than the body of the perithecium, with radial cracks around the ostiole; exciple 0.1-0.2 mm across, the wall colourless to pale brown in upper part; hymenial gel hemiamyloid, I+ red (I+ blue at very low concentrations of I), K/I+ blue; hamathecium of periphyses in the ostiolar canal, and short periphysoids in the upper half of the perithecial cavity; paraphyses dissolving early. Asci 8-spored, two-layered, fissitunicate, with a thin tholus reacting I-, Verrucaria-type. Ascospores 1-celled, hyaline, ellipsoid, poorly developed (no mature ascospores ever observed). Photobiont chlorococcoid. Spot tests: thallus K+ dark blue-green, C-, KC-, P-. Chemistry: a pink pigment in thallus.
Note: a chiefly Mediterranean lichen of steeply inclined, hard calcareous rocks, absent from non-natural habitats; according to Roux (in litt.), contrary to B. parmigerella, this species does not grow on dolomite. The species is easily confused with B. marmorea.