Description: Thallus crustose, thin, smooth, white to pale grey or more rarely ochraceous, forming small patches or mosaics, sometimes delimited by a dark prothallus. Apothecia lirelliform, 0.3-2.2 x 0.1-0.2(-0.3) mm, black, epruinose, distinctly raised, usually numerous, simple or frequently branched, scattered or often contiguous, with a peristently slit-like disc. Proper exciple black, carbonized, extending below the hymenium, K+ olive-green; epithecium brown or green-brown, K+ olive-green; hymenium colourless, I+ blue; paraphysoids septate and anastomosed, to 1 µm thick; subhymenium pale brown; hypothecium black, carbonized. Asci 8-spored, clavate-subglobose, semi-fissitunicate, Arthonia-type. Ascospores 3-septate, hyaline, ellipsoid to ovoid, 12-18(-20) x (2.5-)3-4(-5) µm, with a thin, often poorly evident gelatinous perispore. Pycnidia rare, immersed, flask-shaped, black. Conidia bacilliform, straight or slightly curved, 4-6 x 0.7-1 µm. Photobiont trentepohlioid. Spot tests: thallus K-, KC-, C-, P-, UV-. Chemistry: without lichen substances.
Note: a widespread temperate lichen, one of the most common epiphytic species of the genus throughout Italy.