Description: Thallus crustose, fully endolithic, usually covering large surfaces, pale pink-purple. Upper cortex (lithocortex) densely prosoplectenchymatous, of conglutinated hyphae intermingled with microcrystals, the upper cells pink-violet; algal layer discontinuous, photobiont cells in clusters; medulla prosoplectenchymatous. Perithecia usually numerous, completely immersed in thallus and leaving pits in the rocks when they fall off, the apex slightly protruding to flattened. Involucrellum present, black, narrower than the body of the perithecium, with radial cracks around the ostiole; excipulum 0.1-0.2 mm diam., colourless to pale pale brown in upper part; hymenium colourless K/I+ blue; hamathecium of periphyses in the ostiolar canal, and short periphysoids in the upper half of the perithecial cavity. 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). Pycnidia not known. 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.