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DescriptionThallus: umbilicate, monophyllous, +circular to irregular in shape, incised (lobate), thin, rigid, brittle, 1-2.5 cm in diam.; upper surface: medium to dark brown or dark gray, with densely packed, high, rounded ridges; medulla: white; lower surface: black, smooth, covered in simple thalloconidia; Apothecia: common in American material, rare in European, black, adnate, gyrose; asci: clavate, usually 8-spored; ascospores: hyaline or brown, simple to muriform, broadly ellipsoid, 7-16 x 5-9 µm; Thalloconidia: simple, dark brown, released directly from lower cortex; Spot tests: medulla K-, C+ red, KC+ red, P-; Secondary metabolites: gyrophoric, lecanoric and umbilicaric acids.; Substrate and ecology: on siliceous rocks, vertical to horizontal faces of large boulders or cliffs in the alpine zone, above the snow in winter; World distribution: Europe, and North and South America; Sonoran distribution: rare, on the high peaks of Arizona.; Notes: Umbilicaria nylanderiana is often confused with U. hyperborea, but that species never has black thalloconidia found in U. nylanderiana. The single celled thalloconidia found in U. nylanderiana separate it readily from U. polyphylla.