Description: Thallus crustose, episubstratic, bullate-areolate or of dispersed, wart-like areoles, slightly shiny, yellowish grey to yellowish white, without a clear prothallus. Areoles usually strongly convex, 0.7-1.5 mm wide, sorediate. Soralia greenish or greyish black to dark blue-green, discrete, round and laminal to elongate and marginal, level with thallus or slightly excavate, 0.5-1.5 mm wide; soredia granular, 35-50 µm. Apothecia rare, lecanorine, sessile to slightly constricted at base, 0.8-1.5 mm across, with a dark greyish brown, epruinose disc, and a prominent, more or less flexuose thalline margin sometimes blackening on inner rim. Thalline exciple corticate, containing large, irregular crystals visible under polarized light; epithecium yellowish brown, K+ olivaceous green, with a granular surface; hymenium colourless, 45-55 µm high; paraphyses slightly branched in upper parts, not capitate; 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, 9-15 x (5-)6-7.5 µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K+ yellow, C-, KC-, P- or P+ faintly yellow, UV-; soralia K+ pale yellow. Chemistry: atranorin (major), chloratranorin (minor), roccellic acid and gangaleoidin (traces), and sometimes unidentified fatty acids.
Note: on hard siliceous rocks, also on man-made substrata in the Alps, especially on vertical faces; very much overlooked, or confused with other species.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)