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DescriptionThallus: to 2-3.5 cm across, umbilicate, monophyllous, becoming deeply lobed, or ± polyphyllous and pulvinate; lobes: c. 1-3 mm across, plane to concave or less often convex, c. 0.5-1 (-1.5) mm thick, crenate-incised; upper surface: pale greenish yellow, light yellow, yellowish gray, pale yellowish green, or light gray to whitish, scarcely changed in herbarium, smooth or powdery; edges concolorous or often at least partly blackened; Apothecia: laminal or submarginal, often numerous and crowded, to 0.8-2.5 mm diam., adnate then sessile, constricted at base; disc: plane to convex, reddish orange to moderate or strong orangish yellow or yellow, at least partly weakly to densely pruinose and appearing light orange to light orange-yellow; thalline exciple: 0.1-0.4 mm wide, entire to flexuous or crenate towards inside, ± raised then level, persistent or excluded, concolorous with thallus or yellower, or slightly orangish when young; hymenium: c. (35-) 50-60 µm tall, ± yellowish or orangish, not inspersed, but usually with superficial layer of granules; paraphyses tips: hyaline, c. 2-3 µm wide; ascospores: ellipsoid to oblong-ellipsoid, c. 8.5-12 x 3.5-6 µm; Pycnidia: rare; conidia: 15-20 (-30) µm long; Spot tests: upper cortex: K- or K+ yellow, C-, KC+ yellow, P-, UV-, medulla: K-, C- or C+ red, KC- or KC+ red, P-, or P+ yellow, UV-; Secondary metabolites: upper cortex: with usnic acid, ± either placodiolic or pseudoplacodiolic acid; medulla: with aliphatic acids or no substances, or, at lower latitudes (including the Sonoran region), occasionally psoromic or lecanoric acid chemosyndromes, or both.; Substrate and ecology: usually on hard, siliceous rocks (including granite, schist, quartz, mica, basalt), sometimes sandstone, and occasionally calcareous rocks; from pinyon-juniper woodland up into the alpine zone; frequently nitrophilous; World distribution: circumarctic, circumboreal to warm-temperate, Eurasia, North America (except temperate eastern N. America); reports from the Southern Hemisphere appear to be based on misidentifications; Sonoran distribution: Arizona, California, Baja California and Chihuahua; common at moderate to high elevations, 1200-3200 m.; Notes: This species is distinguished from R. melanophthalma and R. peltata by the combination of persistently whitish to yellowish upper surface and reddish to yellowish pruinose discs (with correspondingly tinged hymenium). In contrast to the holotype of R. chrysoleuca (L!) and many other specimens from northern areas of North America and Eurasia, Sonoran region material usually has rather thick lobes with plane to down-turned and unthickened edges, with greenish, bluish, or blackish coloration absent or restricted to parts of the underside next to the edges, making the material occasionally difficult to distinguish from R. subdiscrepans (see notes under that species).