Thallus: foliose, adnate, 3-10 cm in diam., lobate lobes: subirregular, elongate, slightly imbricate, plane, separate, 4-10 mm wide; apices: rotund, often suberect, eciliate upper surface: gray, smooth, dull, emaculate to faintly white maculate, becoming cracked with age soredia: granular, common, in linear to crescent-shaped, marginal or submarginal soralia; isidia and pustulae: absent medulla: white with continuous algal layer lower surface: black with brown to mottled ivory naked zone peripherally, centrally rhizinate; rhizines: scattered, simple Apothecia: rare, substipitate, up to 10 mm in diam.; margin: sorediate; disc: brown, imperforate ascospores: ellipsoid, 15-21 x 7-10 µm Pycnidia: rare, punctiform conidia: sublageniform, 7-8 x 1 µm Spot tests: upper cortex K+ yellow, C-, KC-, P-; medulla K-, C-, KC-, P- Secondary metabolites: upper cortex with atranorin and chloroatranorin; medulla with protopraesorediosic and praesorediosic acids (major), unknown fatty acids (minor). Substrate and ecology: on rocks and trees in open habitats World distribution: pantropical and pantemperate Sonoran distribution: thorn forests of Sonora, Sinaloa and southern Baja California Sur. Notes: Originally the species was reported to have caperatic acid (Hale 1965), but subsequent investigation has shown the fatty acids to be unique (Elix 1994k).