Thallus: 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.