Thallus: 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.