Description: Thallus crustose, endosubstratic, smooth, whitish, pale grey or bluish green, without a distinct prothallus. Apothecia completely immersed in the rock, lecideine, blue-black to black, often irregular in outline, 0.4-0.8(-1) mm across, with a concave to flat disc and a thin, raised, finally excluded proper margin. Proper exciple poorly developed, very thin, mostly colourless, somehow thicker and blue-green in upper part; epithecium blue-green, N+ purple, K-; hymenium colourless or pale blue-green in upper part; paraphyses thread-like, sparingly branched, submoniliform in upper part, not thickened at apex; hypothecium colourless. Asci 8-spored, broadly clavate, with a uniformly K/I+ blue tholus without an ocular chamber, surrounded by a thick, gelatinous, I+ blue sheath. Ascospores 1-celled, hyaline, ellipsoid, (9-)11-15 x (7-)9-12 µm. Pycnidia mostly arising at the periphery of the thallus, with a blue-green, N+ purple wall. Conidia short-bacilliform, straight to slightly curved, 4.5-5(-7) x 0.7-1 µm. Photobiont chlorococcoid, the cells 7-12 µm wide. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: thallus without lichen substances.
Note: on limestone near the ground, such as on basal parts of steep cliffs in upland areas; certainly more widespread in the Alps, where it is locally common. According to Tretiach (2015f), the records from Veneto reported by Nimis (1994), and Nascimbene & Caniglia (2000, 2003c) refer to another species.