Description: hallus crustose, inapparent or thinly episubstratic, when developed rimose-areolate, dirty white to grey, often delimited by a dark prothallus. Apothecia zeorine, 1-2(-3.5) mm across, sessile and strongly constricted at base, with a flat to finally strongly and often irregularly convex, at first blackish, finally often pale brown, epruinose disc, the thalline margin thin, raised, blackish to greyish, often dark bluish black especially around the disc, usually persistent but finally sometimes excluded. Thalline and proper exciples clearly paraplectenchymatous, the thalline exciple usually containing algae in basal parts only, the outer cells brown-walled; epithecium at first black-brown, then brown, N-; hymenium colourless, inspersed with small crystals in upper part, 70-80 µm high; paraphyses slender, 1-2 µm thick at mid-level, the apical cells slightly swollen, up to 5 µm wide; hypothecium colourless, cupulate. Asci 8-spored, clavate, Lecanora-type. Ascospores 1-celled, hyaline, ellipsoid or narrowly ellipsoid, (8-)10-16 x (3-)4.5-6(-7) µm. Pycnidia rare, black, projecting with the apical part. Conidia thread-like, curved, 15-30 x 0.5-1 µm. Photobiont chlorococcoid. Spot tests: K-, C-, KC- or KC+ weakly yellow (microscopic slide!), P-. Chemistry: thallus with low amounts of usnic and rangiformic acids.
Note: on steep faces of various types of schist including those rich in iron, mostly at high elevations; widespread in the Alps but rare, with no record from Italy; to be looked for in the Italian Alps. The species, which contains usnic acid, does not belong into Polyozosia (see Roux et coll. 2017).