Distribution: N - Frl (Tretiach & Hafellner 2000), Ven (Nimis 1994), TAA, Lomb, Piem (TSB 33717), VA (Piervittori & Isocrono 1999). C - Tosc (Benesperi 2007), Abr (Nimis & Tretiach 1999, Di Nuzzo & al. 2021, Gheza & al. 2021, Vallese & al. 2022), Mol (Nimis & Tretiach 2004, Caporale & al. 2008, Brackel 2020), Sar. S - Camp (Nimis & Tretiach 2004), Cal (Puntillo 1996), Si.
Description: Thallus squamulose to subcrustose, brownish to greenish grey-brown, often faintly pruinose, never darker at margin, 0.16-0.36 mm thick. Squamules 1-4 mm broad, flattened, smooth, contiguous, not imbricate, usually forming a rosette-like thallus reaching 9 cm in diam., developing on a black hypothallus; marginal squamules often elongated, rounded and often somewhat concave at tips, always epruinose; edge of squamules crenulate, concolorous with upper surface. Lower surface dark, attached by 3-4(-4.5) µm thick, dark rhizohyphae. Upper cortex thin, paraplectenchymatous, poorly delimited from the algal layer; medulla loose, of a mixture of elongated and spherical hyphae; lower cortex absent, the medulla becoming darker in lower part. Perithecia laminal, pyriform, immersed, not flattened, 0.2-0.3 mm across, without involucrellum. Exciple colourless to brownish, especially near the ostiole; paraphyses absent, substituted by periphyses. Asci 8-spored, unitunicate, clavate, thin-walled, not or only slightly thickened at apex, without ocular chamber, the wall I-. Ascospores 1-celled, hyaline, clavate, thin-walled, (15-)17-22(-24) x (5-)6-8(-9) µm, biseriately arranged in the asci. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a boreal-montane to arctic-alpine, circumpolar species found on plant debris, mosses and bare, humus-rich soil on calciferous ground near or above treeline; perhaps less common than C. cinereum in the mountains of southern Italy.
Growth form: Squamulose
Substrata: soil, terricolous mosses, and plant debris