Description: Thallus crustose, episubstratic, pale yellow-green to green-grey, more rarely darkening to green-brown or green-black, areolate, forming more or less well-delimited patches to 2 cm diam. Areoles flattened, the marginal ones sometimes almost subsquamulose, often with crenulated margins, bearing 1-2 mm wide, discrete and circular to confluent soralia which are usually slightly paler than thallus; soredia 30-50 µm. Apothecia rare, lecanorine, 0.2-0.5 mm across, sessile, with a flat to slightly convex, yellowish to green- or brown-black disc, and an entire to crenulate, finally excluded thalline margin. Epithecium brown, without crystals; hymenium colourless; paraphyses simple or sparingly branched in upper part, with slightly swollen apices; 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, 7-13 x 4-7 μm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC+ yellow, P-, UV+ dull orange. Chemistry: usnic acid, zeorin.
Note: on iron-rich rocks, including pebbles, in upland areas; certainly more widespread in the Alps. A dubious record from Lazio (see Nimis 1993: 369) is not accepted here.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)