Description: Thallus crustose-subsquamulose, heteromerous, episubstratic, bluish grey to olive-brown, of 2-3 mm wide, contiguous or imbricate, sorediate areoles/squamules with a white-felted, upturned margin, developing on a thin, often inconspicuous, blue-black hypothallus usually forming a thick, cracked crust. Soredia granular, lead-grey ot violet-grey, arranged in marginal, sometimes finally confluent soralia, which often appear woolly in herbarium material (accumulation of fine crystals). Upper cortex sclerenchymatous, 30-40 µm thick, of thick-walled cells. Apothecia very rare, lecanorine, 0.5-1.5(-2) mm acrosss, with a brown disc and a sorediate thalline margin. Proper exciple subparaplectenchymatous; epithecium pale brown; hymenium colourless, up to 100 µm high, I+ blue-green turning reddish; paraphyses simple, coherent, slightly swollen at apex; hypothecium colourless. Asci 8-spored, subcylindrical to clavate, with a I+ blue tholus and an internal, more intensely I+ blue structure. Ascospores 1-celled, hyaline, ellipsoid, with a thick epispore and broadly attenuated apices, 13-16 x 7-8 µm without epispore, 17-23 x 8-9 µm with epispore. Photobiont cyanobacterial (Nostoc, the cells in clusters). Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: terpenoids and aliphatic acids.
Note: a mild-temperate to Mediterranean species found on bark of ancient broad-leaved trees in semi-natural, rather undisturbed, humid woodlands, more rarely on siliceous, mossy rocks; mosty Tyrrhenian in Italy.