Distribution: N - Frl (Tretiach & Carvalho 1995), Lig (Giordani & al. 2009, Giordani & Incerti 2008).
Description: Thallus crustose, episubstratic, mostly continuous, smooth to rough or verruculose, white, yellowish white or pale grey, sometimes delimited by a black prothallus. Apothecia lecanorine, at first immersed in thallus, later sessile and constricted at base, 0.7-1.5(-2) mm across, with a pale to dark red-brown, flat to slightly convex disc, and a relatively thick, distinctly and deeply crenulate thalline margin. Thalline exciple corticate, the cortex basally slightly thickened, the medulla with 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 orange-brown, with coarse crystals soluble in K and N, P+ orange-red (with the formation of crystals); hymenium colourless, 50-90 µm high; paraphyses weakly branched and anastomosing, 2-3 µm thick at mid-level, slightly thickened at apex; hypothecium colourless, 30-80 µm high. 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, (7.5-)10-14.5 x (6-)7-8.5(-10) µm, the wall 0.5-1 µm thick. Conidia cylindrical. 10-14 µm long. Photobiont chlorococcoid. Spot tests: thallus K+ yellow, C-, KC-, P-; apothecial margin and disc P+ orange-red. Chemistry: thallus with atranorin (major), and variable amounts of placodiolic acid, especially concentrated in the apothecial margin; epithecium with pannarin.
Note: a very rare species found on the smooth bark of old deciduous trees, especially Fagus, more rarely Abies, in humid montane forests. It is included in the Italian red list of epiphytic lichens as “Critically Endangered” (Nascimbene & al. 2013c).