Description: Thallus crustose, endosubstratic or thinly episubstratic, 0.1-0.3(-0.8) mm thick, poorly evident or rimose-areolate and dirty white, without a clear prothallus. Medulla white, I-. Apothecia lecideine, black to brown-black (especially when wet), 0.2-0.9 mm across, often in groups, with a strongly convex disc and a thin, very soon excluded proper margin. Proper exciple bluish-green in outer part, colourless within; epithecium bluish-green to grey-green, 12-20 μm high, K-; hymenium colourless, 50-70 μm high, I+ blue; paraphyses relatively coherent in water, rather lax in K, c. 1.7 μm thick at base, progressively thickening to c. 3.5 μm in upper part, the apical cells to 6 μm wide; hypothecium colourless. Asci 8-spored, clavate, very thin-walled, with a K/I+ blue, tall tholus penetrated by a faintly amyloid apical cushion, the wall K/I-, surrounded by a blue outer layer. Ascospores 1-celled, hyaline, narrowly ellipsoid to oblong-ellipsoid, often biguttulate and apparently 1-septate, 12-24 x 4-7 μm, 2.5-3.5 times as long as wide. Pycnidia black, half-immersed in thallus. Conidia thread-like, 12-25 x c. 0.8 μm. Photobiont chlorococcoid. Spot tests: thallus and medulla K- or rarely K+ weakly yellow, C-, KC-, P-. Chemistry: not known.
Note: a poorly known calcicolous species reported from the Alps, the Tatra Mnts., and Spitsbergen, with optimum near or above treeline.