Description: Thallus minutely foliose to subsquamulose, bright lemon yellow, paling to yellow-green in shade, forming rosettes to 5 mm wide, often coalescing into colonies up to 30 cm across. Lobes narrow and short, subsquamulose, 0.1-0.6 mm wide, adnate or ascending, dorsiventral, sparse to imbricate, with granular blastidia ((35-40 μm wide), most common on the more or less fan-shaped ends. Upper cortex c. 10-45 µm thick; medulla white, very thin; lower cortex absent. Lower surface with an arachnoid appearance, white and transparent, showing the green algal layer. Apothecia extremely rare in Europe (not observed in Italian material), sessile, to c. 1 mm diam., with a yellow, plane to finally convex disc, and a smooth but often sorediate margin. Epithecium yellow-brown, granular; hymenium colourless; paraphyses simple, cylindrical to submoniliform; hypothecium colourless. Asci 8-spored, clavate, Candelaria-type. Ascospores simple, guttulate, hyaline, oblong-ellipsoid, 11-16 x 4-6 µm. Pycnidia appearing as raised warts on the thallus surface. Conidia ellipsoid, 2.5-3.5 x c. 1.5 µm. Photobiont chlorococcoid. Spot tests: all negative. Chemistry: probably calycin (major) and pulvinic dilactone (minor).
Note: a recently-described species, which in some parts of Europe, e.g. in Scandinavia, is even more common than C. concolor. Italian material of C. concolor needs revision: from a rapid screening of the TSB material it seems that in Italy this species is rarer than C. concolor.
Growth form: Foliose, narrow lobed
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)