Thallus: umbilicate, usually monophyllous, +circular, rigid, 1-3(-6) cm in diam. upper surface: medium to dark brown, smooth to strongly verrucose medulla: white lower surface: pale brown to almost black, often with cavities Apothecia: common, black, adnate to sessile, gyrose, up to 2 mm in diam. asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, 8-15 x 4-8 µm Spot tests: medulla K-, C+ red, KC+ red, P- Secondary metabolites: gyrophoric, lecanoric and umbilicaric acids. Substrate and ecology: on siliceous rocks, often on fairly horizontal surfaces on small or larger boulders or cliff outcrops, usually snow-covered in winter World distribution: Europe, Asia, North America, and Australia Sonoran distribution: scattered, mostly in the boreal to alpine vegetation zone of the high peaks of Arizona, California, and Baja California. Notes: Umbilicaria hyperborea is often confused with U. nylanderiana, but the latter species always have single-celled thalloconidia in patches or covering the entire lower surface.