Thallus: umbilicate, monophyllous, +circular, thick, rigid, often folded, 1-4(-9) cm in diam. upper surface: light to dark brown to grayish olive, smooth to obscurely wrinkled to sometimes cracked, dull to somewhat shiny, marginally pruinose lower surface: dark brown to black, coarsely papillate where not densely covered with ivory white slender, branched rhizinomorphs medulla: white Apothecia: common, black, sessile, angular to star-shaped, gyrose, up to 2 mm in diam. asci: clavate, 8-spored ascopores: hyaline, simple, ellipsoid to broadly ellipsoid, 12-20(-29) x 7-15(-18) µm Spot tests: medulla K-, C+ red, KC+ red, P- Secondary metabolites: gyrophoric, lecanoric, and hiascic acids. Substrate and ecology: on dry, exposed, siliceous rocks World distribution: the west coast of North America, scattered from California to Alaska Sonoran distribution: scattered in the coastal ranges of southern California. Notes: Umbilicaria angulata, a species endemic to the west coast of North America, is very similar to U. phaea. The major difference is the rich development of rhizinomorphs on the lower surface of U. angulata. Umbilicaria phaea also seems to have a tolerance for even drier, inland habitats. According to Llano (1950) the spores may become muriform in U. angulata.