Description: Thallus crustose, episubstratic, areolate, forming large patches to 15 cm diam. Areoles irregular, usually angular, flat to strongly convex in some forms, whitish grey to pale grey-brown or ochre-coloured, usually paler at margins, separated by deep cracks. Apothecia lecanorine-aspicilioid, round to angular or almost linear, immersed, 2-3 per areole, 0.2-1 mm wide, with a concave to flat, black, usually epruinose disc (but pruinose in some forms with verrucose areoles), and a thin to rather thick thalline margin. Epithecium green to olive-green or greenish brown, N+ brighter green; hymenium and hypothecium colourless, I+ blue to reddish, the hypothecium not subtended by an algal layer; paraphyses coherent, scarcely swollen, to 2 µm wide at tips. Asci (6-)8-spored, clavate, the thin outer coat K/I+ blue, the wall and apical dome K/I-. Ascospores 1-celled, hyaline, broadly ellipsoid, (20-)22-28 x 11-14 µm, thin-walled, 1-2 seriate in the asci. Pycnidia with a black, punctiform ostiole and a colourless wall. Conidia bacilliform, straight, 7-12 x c. 1 µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K+ yellow turning red (needle-like crystals), C-, KC-, P+ yellow-orange. Chemistry: norstictic, connorstictic and constictic acids.
Note: on more or less base-rich siliceous rocks wetted by rain. Common in Mediterranean Italy, rare or absent only along the Adriatic side of the Peninsula, mainly because of the scarcity of suitable substrata. Most of the other records from the Alps, especially those from high altitudes, are likely to refer to Aspilidea myrinii (Malícek in litt.) or to other species. According to Zakeri & al. (2019) in Eurasia there are several different cryptic species, but all samples from the Mediterranean region belong to the same clade.