Description: Thallus crustose, episubstratic, areolate-subsquamulose, yellowish grey to sulphur yellow, forming continuous crusts or more rarely consisting of dispersed, flat to slightly convex, crenulate, 0.5-1.5(-3) mm wide areoles with marginal, bright sulphur-yellow, finely granular, 30-70 μm thick soredia which rarely coalesce into a sorediate crust. Apothecia rare, lecanorine, 0.2-0.8 mm across, sessile, more or less immersed amongst the soredia, with a concave to flat, red-brown to olivaceous brown, epruinose disc, and a well-developed, persistent, often sorediate thalline margin. Epithecium red-brown to olive-green, with a few granules; hymenium colourless, 45-60 μm high; paraphyses mostly simple, slightly thickened at apices; hypothecium colourless, inspersed with oil droplets. Asci 8-spored, clavate, Lecanora-type. Ascospores 1-celled, hyaline, broadly ellipsoid to subglobose, 7-10 x 6-8 μm. Photobiont chlorococcoid. Spot tests: K-, C-, KC-, P+ orange-red, UV+ bright orange. Chemistry: rhizocarpic acid, pannarin, zeorin.
Note: on iron-rich rocks, including pebbles. A dubious record from M. Etna (see Nimis 1993: 370) 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)