Description: Thallus foliose, heteromerous, dorsiventral, closely adnate, forming up to to 10 cm wide patches. Lobes 0.5-2.5 mm wide, slightly concave to flat, with thicker, slightly up-turned margins. Upper surface dark brown to black (greenish brown in shade-forms), more or less shiny, with whitish, rounded to elongate, laminal and/or marginal pseudocyphellae; lower surface whitish to pale brown, darker along margins, somewhat wrinkled, with simple rhizines. Upper cortex paraplectenchymatous, with a non-pored epicortex, the cell walls containing isolichenan; medulla white. Apothecia common, lecanorine, laminal to submarginal, the disc concolorous with thallus, to 5 mm across. Epithecium brownish; hymenium and hypothecium colourless. Asci 8-spored, broadly clavate, clavate, the K/I+ blue tholus penetrated by a faintly amyloid apical cushion with parallel or diverging flanks, the wall K/I-, surrounded by a K/I+ blue outer layer, Lecanora-type. Ascospores 1-celled, hyaline, ellipsoid, 6.5-8.5 x 5-6.5 µm. Pycnidia common, black, sessile with a widened base. Conidia dumbbell-shaped (thickened at both ends), 5-7.5 x 1-1.5 µm. Photobiont chlorococcoid. Spot tests: upper cortex and medulla K-, C-, KC-, P-, N-, UV-. Chemistry: without lichen substances.
Note: a rather neglected, arctic-alpine and circumpolar species described from Italy and also known from Switzerland and France, growing on acid siliceous rocks near and above treeline. The type, collected by Arnold, is from the surroundings of Brenner Pass in South Tyrol.