Distribution: N - Frl (Tretiach & Hafellner 2000), Ven, TAA (Nascimbene & al. 2022), Lomb, VA (Piervittori & Isocrono 1999). C - Tosc, Sar (Scheidegger 1993).
Description: Thallus crustose, episubstratic, often growing on the thalli of Schaereria fuscocinerea, pale to dark grey, shiny, forming 1-4(-5) cm wide patches, often delimited by a dark prothallus. Cortex of anticlinally arranged, cellular hyphae, the terminal cells swollen, with brown caps; medulla white, I+ blue. Apothecia black, cryptolecanorine to zeorine, 0.2-0.8(-1) mm across, immersed in the thallus. Proper exciple thin, aethalea-type, the inner hyphae hyaline, prosoplectenchymatous, the outer hyphae parallel and usually strongly brown-pigmented, N-; epithecium olive-green to olive-brown, N+ red; hymenium colourless, not inspersed with oil droplets, 42-70 µm high; hypothecium colourless to medium brown. Asci 8-spored, clavate to cylindrical-clavate, the apical dome K/I+ dark blue with a pale, conical-pointed apical cushion (axial mass), the wall I-, but the thin outer gel I+ blue, Bacidia-type. Ascospores 1-septate, constricted at septum, brown, broadly oblong, 8-12 x 4.5-6.5 µm, Buellia-type, the wall >1.5 µm thick, with a striate ornamentation. Pycnidia black, immersed in the thallus. Conidia bacilliform, 3.5-4 x 1-1.5 µm. Photobiont chlorococcoid. Spot tests: thallus K- or K+ yellow-orange, C+ red, KC+ red, P-. Chemistry: gyrophoric acid (major), variable amounts of stictic acid.
Note: a mainly arctic-alpine, circumpolar species found on hard, lime-free siliceous rocks, predominantly on inclined to subvertical faces wetted by rain in upland areas, with optimum above treeline; the species is most common in the Alps, rarer in the high Mediterranean mountains, and seems to be facultatively parasymbiotic.