Thallus: foliose, tightly adnate to adnate, 4-10 cm in diam., dichotomously lobate lobes: sublinear to subirregular, elongate, plane to subconvex, separate, contiguous to slightly imbricate, black-rimmed, 1-2 mm wide, not lobulate; apices: subrotund to subtruncate, smooth to crenate, eciliate upper surface: dark yellow-green, smooth, shiny, epruinose and emaculate, without soralia, isidia, or pustulae medulla: white, with continuous algal layer lower surface: black, plane, sparsely to moderately rhizinate; rhizines: black, simple, 0.2-0.4 mm long Apothecia: common, substipitate, 1-2 mm wide, laminal on thallus; disc: cinnamon-brown to dark brown; margin: smooth, pruina absent asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, 10-12 x 5-6 µm Pycnidia: common, immersed conidia: bifusiform, 5-6 x 1 µm Spot tests: upper cortex K-, C-, KC-, P-; medulla K-, C-, KC-, P+orange Secondary metabolites: upper cortex with usnic acid (major); medulla with fumarprotocetraric acid (major), succinprotocetraric acid (minor or trace), and sometimes physodalic acid (trace). Substrate and ecology: on acidic rocks, often in semi-open, woodland habitats World distribution: south central U.S.A. and extending into northern Mexico in North America Sonoran distribution: rarely at intermediate elevations in Arizona. Notes: Xanthoparmelia hypomelaena is superficially similar to X. novomexicana, but the latter is distinguished by its brown lower surface and the absence of succinprotocetraric acid in the medulla. The Australian X. hypomelaenoides Elix & J.Johnst. is chemically identical, but has apically rotund, subirregular lobes.