Distribution: N - Frl (Tretiach & Hafellner 2000), Ven (Hertel & Schuhwerk 2010), TAA (Thor & Nascimbene 2007, Hafellner 2021, Nascimbene & al. 2022), Lomb, Piem (Isocrono & al. 2004, 2006, Isocrono & Piervittori 2008), VA (Piervittori & Isocrono 1999, Piervittori & al. 2001), Emil (Fariselli & al. 2020). C - Sar. S - Camp (Aprile & al. 2002), Si.
Description: Thallus crustose, mostly endosubstratic, grey to whitish, poorly evident. Medulla I-. Apothecia lecideine, black, somehow glossy, dispersed or in small clusters, sessile and slightly constricted at base, 0.1-1(-1.2) mm across, at first round, then often angular, with a concave to flat, sometimes umbonate disc, and a distinct, persistent, raised, undulate proper margin. Proper exciple brown-black throughout; epithecium bright blue green to emerald green, 15-25 μm high, N+ purple-red; hymenium colourless to bluish green especially in upper part, 40-75 μm high; paraphyses simple, conglutinated, forked and anastomosing in upper part, 1.7-2.5 µm thick at mid-level, the apical cell hardly swollen; hypothecium brown-black, paler than exciple, to 120 μm high. Asci 8-spored, clavate, the K/I+ blue tholus penetrated by a faintly amyloid apical cushion with parallel or diverging flanks, the outer wall very thin, K/I-, surrounded by a K/I+ blue outer layer, Lecanora-type. Ascospores 1-celled, hyaline, narrowly ellipsoid to oblong, 8.5-15 x 3.5-5.5 µm. Pycnidia black, globose, immersed. Conidia thread-like, 14-30 µm long. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P- or P+ red. Chemistry: thallus without lichen substances or with argopsin.
Note: an arctic-alpine, circumpolar species found on steeply inclined faces of lime-poor sandstone, schists and gneiss, rarely on dolomite, in upland areas; common in the Alps, much rarer in southern Italy.