Thallus: foliose to subfruticose, forming small cushions up to 3 cm wide or extensive colonies, lobate lobes: dorsiventral to subterete, 0.2-0.5 mm wide; tips: 0.1-0.3 mm wide, ±terete upper surface: yellow to light orange, smooth to somewhat coarse, often wrinkled, sorediate soredia: granular, blastidious, marginal to submarginal or XANTHORIA at lobe tips medulla: white, reticulate, with short to elongate hyphae lower surface: white to yellow, somewhat wrinkled, rarely with short, white hapters Apothecia: rare, laminal or appearing terminal, stipitate, up to 4 mm in diam.; margin: smooth but often sorediate or lobulate; disc: orange; epihymenium: brown, c. 10 µm thick; hymenium: hyaline below, 60-90 µm tall; hypothecium: hyaline to pale brown, 25-70 µm thick; paraphyses: simple or branched, cylindrical, septate asci: clavate, 8-spored ascospores: ellipsoid, polarilocular, hyaline, 12-15 x 5.5-8 µm; septum: 3-6 µm wide Pycnidia: common, immersed, concolorous with upper surface or slightly darker conidia: ellipsoid, 2.3-3 x 1-1.5 µm Spot tests: upper surface K+ purple, C-, KC-, P- Secondary metabolites: parietin (major), fallacinal, emodin, teloschistin and parietinic acid. Habitat and ecology: on bark, rock, and detritus, generally sun-exposed and nutrient rich World distribution: circumpolar and into temperate regions on the subantarctic islands Sonoran distribution: scattered in Arizona, southern California and northwestern Baja California. Notes: Xanthoria candelaria is a very variable taxon occurring on a wide variety of substrates, and it is in need of taxonomic revision throughout its distribution area. In the Sonoran region, X. candelaria is most likely to be confused with X. tenuiloba and X. ascendens. The lobes of X. tenuiloba are very narrow and variable, and the color is mostly pale gray or dull and very rarely as brightly pigmented as in X. candelaria. See also notes for X. ascendens.