Substrate and ecology: on sandstone; World distribution: southwestern North America and possibly in Central Asia; Sonoran distribution: Arizona at 1645-2380 m.; Notes: Most Sonoran material appears to be this variety, which differs from the typical one by: 1) thallus forming larger (3-5 cm) and flatter rosettes; 2) upper surface +dull, pruinose, and rimose; 3) thallus center squamulose-areolate (rather than bullate-areolate); 4) lobes tightly adnate, becoming highly convex and flabellately (rather than irregularly) divided; 5) apothecia somewhat larger (often to 2 mm in diam.), restricted to thallus center; 6) discs dull, usually paler and more yellow; 7) thalline margin raised when young and only gradually excluded. Var. christoi tends to occur especially in the foothills of the south-central Rocky Mountains, while the typical variety is more common in the Great Basin and foothills of the Cascades. However, the varieties appear to intergrade completely.
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