Description: hallus crustose, usually thin and smooth, white to pale grey. Apothecia lecanorine, sessile or slightly constricted at base, 0.4-1.3 mm across, with a brown to very dark brown (almost black) disc and a smooth, raised thalline margin. Thalline exciple corticate, the cortex < 40 μm thick , pulicaris-type, the medullary part with abundant, very large crystals insoluble in K, often intermixed with small crystals soluble in K (in poorly developed apothecia crystals may be sparse or absent); epithecium reddish brown, with abundant, fine crystals dispersed between paraphyses, which are soluble in K but not in N; hymenium colourless, 60-90 µm high; paraphyses slightly thickened at apex (up to 3.5 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, (10-)11-15(-16) x (6.5-)7.5-10 µm, the wall c. 0.8-1 µm thick. Photobiont chlorococcoid. Spot tests: thallus and apothecial margin K+ yellow, C-, KC-, P+ red. Chemistry: atranorin (major), fumarprotocetraric acid or roccellic acid.
Note: a cool-temperate to boreal-montane, circumpolar lichen found on conifers, more rarely on broad-leaved trees, and on lignum; most common in the Alps, rarer in the mountains of southern Italy. The record from Rome by Munzi & al. (2007) is not accepted here pending confirmation.