Distribution: N - Ven (Watson 2014), TAA, Lomb, Piem (TSB 33411), Emil (Fariselli & al. 2020). C - Tosc, Mol (Nimis & Tretiach 2004, Caporale & al. 2008). S - Camp (Garofalo & al. 2010), Pugl.
Description: Thallus crustose, episubstratic, continuous or finely granulose and composed of small goniocysts, yellowish white to greenish, sometimes poorly evident. Apothecia lecideine, 0.3-0.8 mm across, brown-black to black when dry, brown to red-brown and with a darker margin when wet, at first semi-immersed, then sessile and constricted at base, with a flat to more or less convex disc, and a blackish, initially raised, finally often excluded proper margin. Proper exciple dark violet-brown, K+ purple-violet, paler or colourless in outer part, of anticlinaly arranged, large, thick-walled cells; epithecium colourless to pale brown, without crystals; hymenium colourless, 50-70 µm high; paraphyses simple or sparingly and shortly branched in upper part, coherent, 1.5-2(-2.5) µm thick, the apical cells not markedly swollen; hypothecium dark violet-brown, K+ purple-violet. Asci 8-spored, cylindrical-clavate, surrounded by a gelatinous I+ blue coat, with a well-developed I+ blue tholus, a I+ darker blue tube and a well-developed ocular chamber, approaching the Bacidia-type. Ascospores 0-1-septate, hyaline, oblong-ellipsoid, (8-)9-17(-20) x 3-4.5 µm. Photobiont chlorococcoid, with slightly elongated cells. Spot tests: thallus K-, C-, KC-, P-, UV- Chemistry: unknown, but probably thallus without lichen substances.
Note: a mild-temperate species found on steeply inclined to underhanging surfaces of compact calcareous rocks, especially limestone but also calciferous schists, often together with C. minuta.