Description: Thallus crustose, smooth to verrucose, rather thick, usually white. Apothecia lecanorine, (0.6-)1-2.5(-3) mm across, strongly constricted at base, with a reddish brown to orange-brown, usually glossy, concave to finally slightly convex disc, and a thick, raised, often flexuose and crenulate thalline margin. Thalline exciple distinctly corticate, the cortex 30-40 µm thick laterally, 50-75(-90) µm thick at base, not sharply delimited from the medullary part, which is filled with with abundant, small crystals insoluble in K (the crystals reaching the cortex); epithecium orange to orange-brown, the pigment not dissolving in K, without crystals, P-; hymenium colourless; paraphyses slightly thickened at tips to capitate; hypothecium colourless, not inspersed with oil droplets. 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, ellipsoid, (10-)13-19(-21) x (6-)7-10(-11) µm. Pycnidia black, immersed, cerebriform or ovoid. Conidia thread-like. Photobiont chlorococcoid. Spot tests: thallus K+ yellow, C-, KC-, P- or P+ pale yellow. Chemistry: atranorin (major), and unknown triterpenoids.
Note: a mainly temperate lichen found on isolated deciduous trees with base-rich bark, especially Juglans, Acer and Fraxinus, often along roads; most frequent in slightly continental areas, rare or absent in heavily disturbed areas of northern (e.g. the Po-plain) and Mediterranean Italy.