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DescriptionThallus: rather thick, warted-areolate, up to c. 10 cm in diam. but usually smaller; prothallus: absent or present and black; areoles: mostly contiguous (rarely scattered), up to 2 mm in diam.,; surface: light greenish yellow, gray or yellowish white (darkening to brown in the herbarium), convex or flat, occasionally wrinkled; Apothecia: black, 0.5-2(-3) mm in diam.,; disc: black, flat initially, becoming irregularly convex; margin: biatorine, concolorous with the disc; epihymenium: bluish green-black, sometimes in part brown; hymenium: hyaline, 60-80 µm tall; hypothecium: hyaline above and pale yellow-brown below; asci: clavate, 8-spored; ascospores: hyaline, simple, ellipsoid, (7.5-)12-16 x 4.5-8.5 µm; Pycnidia: immersed; conidia: hyaline, 5.5-9 x 1-2 µm; Spot tests: upper cortex: K+ yellow, C-, KC+ yellow, P-; medulla K+ orange, C-, KC-, P+ orange; Secondary metabolites: upper cortex with atranorin and/or usnic acid, medulla with bourgeanic acid and stictic acid.; Substrate and ecology: non-calciferous rock in open habitats, such as alpine areas and scree slopes in upper montane areas; World distribution: temperate to arctic regions of Asia, Europe, and North America; Sonoran distribution: limited to the alpine areas of the highest peaks of Arizona at over 3400 m.; Note: Apparently the Sonoran population is limited to the yellow form of this species. Elsewhere the thallus is frequently white or whitish gray.