Description: Thallus crustose, episubstratic, rather thick, rimose-areolate, the areoles 0.5-2.5 mm wide, grey to brownish grey, often delimited by a dark prothallus. Medulla white, I-. Apothecia biatorine, innate, brown-black, sometimes faintly grey-pruinose (especially along the margins), usually irregular in outline, often elongate, 1-2.5(-3) mm across, with a flat disc and without a distinct proper margin. Proper exciple poorly developed, very thin; epithecium pale brown; hymenium colourless, very thick, scarcely delimited towards the hypothecium, 200-400 μm high; paraphyses simple or sparingly branched in upper part, 1.5-2 μm thick at mid-level, the apical cell clavate, to 5 μm wide. Asci 8-spored, clavate, developing at varying levels, with a thin external and internal K/I+ dark blue cap surrounded by a thick K/I+ pale blue apical cap, and with a K/I- apical tube in tholus, Fuscidea-type. Ascospores 1-celled, at first hyaline but becoming red-brown when overmature, broadly ellipsoid, 8-11 x 5-8 µm. Photobiont chlorococcoid. Spot tests: thallus and medulla K-, C-, KC-, P-, UV+ bluish white. Chemistry: divaricatic acid in the apothecia.
Note: on steeply inclined surfaces of hard siliceous rocks in moderately shaded, humid situations, with optimum near or above treeline.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)