Description: Thallus subfoliose to subfruticose, loosely attached, consisting of dorsiventral, flattened, ascending to erect, strongly channelled and more or less tubular, curved, 0.5-1 mm wide, up to 8-9 cm tall (usually much less), often sparingly branched laciniae bearing short (0.1-0.5 mm), marginal, pycnidia-bearing spinulose outgrowths. Upper surface more or less dark brown, paler in shade-forms, smooth and somehow shiny, the basal parts often reddish; lower surface usually paler, with elongate pseudocyphellae restricted to the margins, particularly evident in the apical parts. Cortex 1-2-layered, with an external layer of thick-walled, paraplectenchymatous cells, and an inner layer of periclinally arranged hyphae; medulla white. Apothecia extremely rare (never found in Italian material), lecanorine, with a brown disc. Asci 8-spored, clavate, Lecanora-type. Ascospores 1-celled, hyaline, ellipsoid 5-9 x 2-4 μm. Pycnidia dark, immersed in the spinules. Conidia fusiform, multiseptate, colourless, 6-7.5 x c. 1 μm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-, UV-. Chemistry: medulla with lichesterinic and protolichesterinic acids.
Note: an arctic-alpine, circumpolar species, with optimum on wind-exposed ridges on siliceous substrata near or above treeline; common throughout the Alps, but much rarer than C. islandica in the Apennines.
Growth form: Fruticose
Substrata: soil, terricolous mosses, and plant debris
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by thallus fragmentation