Description: Thallus crustose, episubstratic, usually forming rounded to irregular patches up to a few cm in diameter, rimose-areolate or (rarely) continuous, sorediate, without a clear prothallus. Areoles discrete or contiguous, greyish or greyish green, up to 0.2 mm in diam., flat to slightly convex, rounded, entire to incised, adnate. Soralia pale yellow to bright yellowish green (paler than thallus), laminal or marginal on the areoles, or originating in non-areolate parts of thallus, discrete to diffuse, often efflorescent, 0.2-0.5 mm across, more or less circular when young to irregular and confluent, often forming a leprose-sorediate, sometimes cracked crust; soredia 15-30(-40) μm in diam. Apothecia rather rare, biatorine, 0.3-0.6(-1) mm across, with a pale yellowish or pinkish brown, sometimes reddish or sordid brown, glossy, flat to strongly convex disc, and a slightly paler, finally excluded proper margin. Proper exciple colourless, 35-80 (-110) μm wide; hymenium colourless, 30-65 µm high; hypothecium colourless. Asci 8-spored, clavate, with a K/I+ blue apical dome penetrated by a narrow, K/I- apical cushion surrounded by a narrow, deeply K/I+ blue zone, the wall K/I- but surrounded by an I+ red-brown, K/I+ blue outer layer, the ocular chamber relatively small, Biatora-type. Ascospores (0-)1-septate, hyaline, narrowly ellipsoid, 9-18(-22) x 3-5 µm. Photobiont chlorococcoid. Spot tests: thallus and soralia K-, C-, KC-, UV-; soralia P+ rapidly orange-red. Chemistry: argopsin (major), norargopsin.
Note: a probably holarctic lichen found on a wide variety of trees with smooth bark, sometimes overgrowing mosses, rarely on lignum, mostly in upland areas; certainly more widespread in the Alps.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)