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DescriptionThallus: crustose, forming orbicular patches up to 1 cm in diam. and irregular in outline, sometimes coalescing into larger patches, forming a thin film over the substrate, or becoming +verrucose, continuous, often delimited by a pale gray to white prothallus; surface: pale grayish green, smooth, glossy, isidiate; isidia: colorless, cylindrical, conical, ampulliform, or subulate, often constricted at base, with the pointed apices sometimes flattened, up to 0.08 mm long and 0.04 mm wide; medulla: not evident; Apothecia: not known in Sonoran material, elsewhere orange-red to black brown, semi-immersed, 0.2-0.4 mm in diam.; disc: pale red-brown, more translucent when wet; margin: smooth to crenate, darker than the disc; exciple: red-brown peripherally, paler internally; hymenium: hyaline below and thinly pale brown above, up to 100 µm tall; asci: cylindrical-clavate, (6-)8-spored; ascospores: hyaline, submuriform to muriform, ellipsoid or ovoid, 20-30 x 6-13 µm; hyphophores: not known; Spot tests: all negative; Secondary metabolites: none detected.; Substrate and ecology: on smooth barked trees in young oak forests; World distribution: Africa (The Canary Islands), western Europe, and North America, particularly in the Pacidic Northwest; Sonoran distribution: southern California, known from one locality in the Santa Ynez Mountains at 375 m.; Note: Vězda (1979) prefers to call the 'isidia' pseudisidia.