Description: Thallus crustose, smooth to slightly verrucose, white to pale grey, sometimes with a yellowish tinge, often delimited by a black prothallus. Apothecia lecanorine, sessile, 0.3-1(-1.8) mm across, with a black, concave to slightly convex disc and a thick, usually smooth, rarely crenulate thalline margin. Thalline exciple distinctly corticate, the cortex basally slightly thickened, with abundant, very large crystals insoluble in K, often intermixed with small crystals soluble in K; epithecium dark green to bluish green-brown, with abundant, coarse crystals soluble in K and N; hymenium colourless, 50-90 µm high; paraphyses slightly thickened at apex (up to 4 µm); 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, Lecanora-type. Ascospores 1-celled, hyaline, broadly ellipsoid, 8-14 x 4-7 µm. Conidia cylindrical, 10-14 µm long. Photobiont chlorococcoid. Spot tests: thallus K+ yellow, C-, KC-, P-; margin of apothecia P- or P+ faintly yellow. Chemistry: thallus with atranorin (major) and gangaleoidin.
Note: several Italian records of this very controversial taxon related to L. chlarotera need reconfirmation; perhaps these are just forms of L. chlarotera with darker apothecial discs.