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DescriptionThallus: foliose, forming small rosettes up to 3 cm wide, adnate, lobate; lobes: dorsiventral, flattened to convex, 0.2-0.5 mm wide; tips: rotund to somewhat pointed, often slightly involute, 0.1-0.4 mm wide; upper surface: yellow to orange, smooth to shiny, not sorediate; medulla: white, reticulate, with short hyphae; lower surface: white, smooth or somewhat wrinkled, with short to long, white to yellow rhizines; Apothecia: common, laminal, stipitate, up to 4 mm in diam.; margin: smooth, mostly with short cilia; disc: orange; epihymenium: brown, c. 10 µm thick; hymenium: hyaline below, 60-95 µm tall; paraphyses: simple or branched, cylindrical, septate; hypothecium: hyaline to pale brown, 10-65 µm thick; asci: clavate, 8-spored; ascospores: oblong to ellipsoid, polarilocular, hyaline, 12-17 x 4.5-8 µm; septum: 1-4(-6) µm wide; Pycnidia: common, immersed to protruding, darker than the upper surface; conidia: bacilliform, 2.8-5 x 1-1.5 µm; Spot tests: upper surface K+ purple, C-, KC-, P-; Secondary metabolites: parietin (major), fallacinal (major), emodin, teloschistin (major) and parietinic acid.; Habitat and ecology: on bark, rarely on detritus, often in dry microclimates, such as montane regions; World distribution: temperate regions in North America; Sonoran distribution: Arizona, at intermediate to fairly high elevations.; Notes: The density and length of rhizines and cilia vary considerable in X. montana. Xanthomendoza montana is similar to X. hasseana; see notes for that species for distinctions. Xanthoria polycarpa has more convex and narrower lobes as well as smaller, ellipsoid conidia.