Distribution: N - Frl (Poelt & Leuckert 1995), TAA (Nascimbene & al. 2006, 2022, Nascimbene 2008b), Lomb (Nascimbene 2006), Piem (TSB 34619), VA, Lig (TSB 33401). C - Marc (Nimis & Tretiach 1999), Abr (Gheza & al. 2021).
Description: Thallus crustose, endosubstratic or thinly episubstratic, whitish to ash-grey, often inconspicuous or developed only around the apothecia. Apothecia lecanorine, usually clustered, sessile, 0.3-0.8 mm across, with a concave to flat, dark brown to black, but heavily bluish-white-pruinose (at least when young) disc, and a smooth, pruinose, pale grey thalline margin. Thalline exciple corticate, 130-140 μm wide, the cortex clearly paraplectenchymatous, greenish and N+ purple in outer and upper parts, filled with granules (visible under polarized light) which are insoluble in K and soluble in N, the medulla rich in algae; proper exciple thin, indistinct; epithecium brown to patchily greenish black, without granules but with a thin epipsamma insoluble in K and soluble in N, the greenish parts N+ purple; hymenium colourless, 70-75 μm high; paraphyses rather thick, mostly simple, submoniliform in upper part, appearing as chains of swollen cells, the apical cells subcapitate; hypothecium colourless or very pale yellow, 70-85 μm high, without granules. 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, (9-)10-14 x 5-6(-7.5) μm. Photobiont chlorococcoid. Spot tests: thallus and apothecial margin K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: on calciferous rocks, often starting the life-cycle on other crustose lichens. A member of the difficult P. dispersa complex, certainly more widespread in the Alps and along the Apennines.