Thallus: crustose, thin, finely granulose, often immersed, dispersed; prothallus: indistinct granules: c. 0.1 mm in diam. surface: white-gray, pale to dark gray or gray-brown, esorediate cortex: absent or thin and indistinct photobiont: globose, 7-13 µm wide Apothecia: broadly adnate, (0.15-)0.3-0.5 mm in diam., not grouped disc: dark brown to black, flat to depressed-convex, epruinose, dull; margin: thin, finally disappearing exciple: lenticularis-type, with mostly thin pale to dark brown marginal zone composed of the pigment caps of the hyphal end cells, not carbonaceous epihymenium: brown-black, K- or almost (sometimes becoming violaceous only for a few minutes, N- hymenium: hyaline, 30-40 µm tall; paraphyses: easily free, not branched, the tips distinctly clavate thickened with dark brown pigment cap (pigment deposited within the hyphal wall); hypothecium: pale brown at least in upper part asci: clavate, c. 35 x 10 µm, 8-spored ascospores: hyaline, becoming 1-septate, oblong-ellipsoid, 8-12 x (2-)2.5-3.5(-4) µm Pycnidia: unknown Spot tests: thallus K-, C-, KC-, P- Secondary metabolites: none detected by TLC. Substrate and ecology: on deciduous trees with acidic bark, often on eutrophic bark of isolated trees, with wide ecological amplitude, in Mediterranean and cool temperate climates World distribution: Europe, western North America, and New Zealand Sonoran distribution: Arizona and southern California.. Notes: Catillaria nigroclavata is similar to C. lenticularis but has a brown hypothecium and occurs on bark. It differs from the also corticolous C. glauconigrans (and C. endochroma) especially in having a lower hymenium. A number of collections identified as this species proved to be misidentifications, including species now placed in other genera (see key above). Superficially it may look like Buellia punctata, whose spores are, of course, brown.