Description: Thallus crustose, pale to dark grey, thin to thick, usually episubstratic, rimose to rimose-areolate, rarely endosubstratic and poorly evident, often delimited by a black, dendritic prothallus. Apothecia micareoid, black, epruinose, sessile and constricted at base, 0.2-0.4(-0.7) mm across, with a usually flat disc and a slightly raised, thin, persistent or finally excluded proper margin. Proper exciple well developed, prosoplectenchymatous, 0.03-0.05 mm wide laterally, consisting of radially arranged, branched and interconnected hyphae, blue-black in outer part, pale brown within; epithecium dull green, K+ green, N+ purple-red; hymenium colourless, 35-50 µm high; paraphyses sparingly branched and anastomosing from the base, 1.5-2.5 µm thick, the apical cells not swollen; hypothecium dark brown, 40-80 µm high. Asci 8-spored, cylindrical-clavate, Psora-type. Ascospores 1-celled, hyaline, narrowly ellipsoid, (6-)7-9(-10) x (2-)3-4(-5) µm. Pycnidia often abundant, c. 0.1 mm wide, grey to black, sessile to half-immersed, with a greenish wall. Conidia cylindrical, 3-6 x 1.5-2 µm. Photobiont chlorococcoid, the cells 10-12 µm wide. Spot tests: K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: on siliceous pebbles in open habitats, ecologically similar to Porpidia crustulata; widespread in the Holarctic region and also recorded from the Southern Hemisphere, with a few records from the Eastern Alps (Austria) outside the Italian territory; to be looked for in the Italian Alps.