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DescriptionThallus: foliose, adnate, 3-10 cm in diam., irregularly lobate; lobes: subirregular, elongate, plane to subconvex, separate, contiguous to somewhat imbricate, (1-)2-3 mm wide, not lobulate; apices: subrotund, smooth to crenate, eciliate; upper surface: yellow-green, smooth, shiny, epruinose and emaculate, moderately to densely isidiate; isidia: abundant, initially globose, soon becoming cylindrical to irregularly inflated, 0.1-0.2 mm in diam., 0.1-0.8 mm tall; tips: epicorticate, dull brown, sometimes weakly erumpent; soralia and pustulae absent; medulla: white, with continuous algal layer; lower surface: pale tan or brown, rarely darkening, plane, moderately to densely rhizinate; rhizines: pale brown, simple, 0.2-0.5 mm long; Apothecia: rare, substipitate, 2-4 mm wide, laminal on thallus; disc: cinnamon-brown to dark brown; margin: smooth, pruina absent; asci: clavate, 8-spored; ascospores: hyaline, simple, ellipsoid, 9-12 x 5-6 µm; Pycnidia: rare, immersed; conidia: bifusiform, 5-6 x 1 µm; Spot tests: upper cortex K-, C-, KC-, P-; medulla K-, C-, KC-, P-; Secondary metabolites: upper cortex with usnic acid (major); medulla with hypoprotocetraric acid (major) and 4-O-demethylnotatic acid (submajor).; Substrate and ecology: on acidic rocks, rarely on wood, usually in open, arid habitats; World distribution: The Arabian Peninsula, Africa and southwestern North America; Sonoran distribution: common at lower elevations in Arizona, southern California, Baja California, Baja California Sur, Chihuahua, and Sonora.; Note: Xanthoparmelia weberi is a broad lobed, globose isidiate species with a pale brown lower cortex and has hypoprotocetraric and 4-O-demethylnotatic acid in the medulla. It is one of the more common isidiate species in the interior deserts.