Description: Thallus crustose-placodioid, episubstratic, firmly attached, rimose-areolate in the centre, lobed at margins, straw-yellow to yellowish greeen, forming rosettes 1-6 cm in diam. Central parts of thallus consisting of flat to bullate, c. 1 mm wide areoles; marginal lobes narrow, contiguous, flat to slightly convex, 2(-3) mm long, up to 1.2(-2) mm wide. Cortex c. 30 µm thick; medulla rather loose, inspersed with granules. Apothecia lecanorine, 1-3(-5) mm across, dispersed or clustered in small groups, with a greenish to brownish green, flat to convex disc, and a persistent, smooth to crenulate thalline margin. Epithecium poorly delimited, yellowish brown; hymenium 60-70 µm high, with yellowish granules; hypothecium colourless. 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, 8-13.5 x 5-8 µm. Photobiont chlorococcoid. Spot tests: thallus K- or K+ indistinctly brownish yellow, C-, KC+ pale yellow, P-. Chemistry: thallus with usnic, rangiformic and norrangiformic acids.
Note: on vertical to underhanging surfaces of hard siliceous rocks, with optimum above treeline; certainly widespread throughout the Alps, where it reaches the nival belt. An earlier record from Marche (see Nimis 1993: 347), being dubious, is not accepted here.