Description: Thallus crustose, fully endosubstratic, usually covering large surfaces, white to pale grey, often delimited by a dark prothalline line. Cortex (lithocortex) densely prosoplectenchymatous, of conglutinated hyphae intermingled with microcrystals; algal layer discontinuous, photobiont cells in clusters; medulla prosoplectenchymatous, sometimes with oil cells (macrospheroids) in the lower part. Perithecia black, flask-shaped, completely immersed in thallus and leaving deep pits in the rocks when they fall off. Involucrellum black, disc-shaped, at first whole, later with radial cracks around the ostiole, narrower than the body of the perithecium (0.2-0.3 mm wide); exciple 0.3-0.4 mm across, the wall mostly colourless, at least at the base; hymenial gel hemiamyloid, I+ red (I+ blue at very low concentrations of I), K/I+ blue; hamathecium of periphyses limited to the periostiolar region, paraphyses dissolving early. Asci 8-spored, two-layered, fissitunicate, with a thin tholus reacting I-, Verrucaria-type. Ascospores 1-celled, hyaline, ellipsoid, often poorly developed, 18-24 x 8-12 µm. Photobiont chlorococcoid. Spot tests: K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a mild-temperate species of compact calcareous rocks in natural, sheltered and shaded situations, with optimum in the submediterranean belt.