Thallus: foliose, pulvinate, loosely adnate, 4-8 cm in diam., irregularly dichotomously lobate; lobes: sublinear, short, plane to subconvex, becoming weakly convoluted, contiguous but often somewhat imbricate, 0.5-1.5 mm wide, lobulate; lobulae: sublinear, often over 0.7 mm long, 0.3-0.5 mm wide, convex; apices: subrotund, smooth to crenate, eciliate; upper surface: yellow-green but darkening with age centrally, smooth, dull, epruinose, usually emaculate but may have diffusely maculate lobe tips, without soralia, isidia, or pustulae; medulla: white, with continuous algal layer; lower surface: pale brown to brown, plane, shiny, moderately rhizinate; rhizines: brown, simple to furcate, rarely dichotomously branched, concolorous with lower cortex, 0.3-1 mm long; Apothecia: rare, sub-stipitate, 1-3 mm wide, laminal on thallus, with a smooth margin; disc: dark brown, concave initially but becoming plane, epruinose; asci: clavate, 8-spored; ascospores: hyaline, simple, ellipsoid, 9-10 x 5-6 µm; Pycnidia: common, immersed; conidia: bifusiform, 6-7 x 0.5 µm; Spot tests: upper cortex K-, C-, KC-, P-; medulla K+ yellow becoming dark orange, C-, KC-, P+ red; Secondary metabolites: upper cortex with usnic acid (major); medulla with stictic acid (major), norstictic and constictic acids (minor), cryptostictic acid (trace) and often with connorstictic acid (trace).; Substrate and ecology: on soil, often in open, arid habitats, in coastal habitats in the Sonoran region; World distribution: North and South America; Sonoran distribution: occasionally at lower elevations in Arizona, near the Pacific coast in southern California and Baja California.; Notes: Xanthoparmelia standaertii is characterized by its terricolous habitat, narrow lobes, abundant secondary lobules, its brown lower cortex, the absence of vegetative propagules and the occurrence of the stictic acid chemosyndrome in the medulla. It could be confused with X. neowyomingica but that species has lobes with a canaliculate lower surface and subterete lobules whereas the lobes are plae to subconvex and the lobules flattened in X. standaertii.