Thallus: foliose, forming medium-sized to large rosettes up to 10 cm wide or sometimes colonies, rather tightly adnate, lobate lobes: dorsiventral, concave to flattened, with a slight marginal border, 0.7-3.5 mm wide; tips: 0.5-1.5 mm wide, rotund to almost flabellate/spathulate upper surface: yellow to orange, smooth, somewhat wrinkled, not sorediate medulla: white, bundled, with elongate hyphae lower surface: white (to yellow), wrinkled, with short, white hapters Apothecia: common, laminal, stipitate, up to 8 mm in diam.; margin: smooth to crenulate; disc: orange; epihymenium: brown, c. 10 µm thick; hymenium: hyaline below, 50-90 µm tall; hypothecium: hyaline to pale brown, 15-50 µm thick; paraphyses: simple or branched, cylindrical, septate asci: clavate, 8-spored ascospores: ellipsoid, polarilocular, hyaline, 12-16 x 5-9 µm; septum: 3-8 µm wide Pycnidia: common or rare, immersed, usually slightly darker than the upper surface conidia: ellipsoid, 2.5-4 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: in the Sonoran area most common on twigs (but also found on volcanic rocks), also occurring on bark, rock, as well as various other substrates (subneutral to basic, rather nutrient rich), often in humid microclimates, such as coastal regions World distribution: circumboreal, southwards reaching into temperate regions, especially in oceanic areas, and also in subantarctic regions, Australasia, and Africa Sonoran distribution: coastal areas of southern California and western Baja California and Baja California Sur. Notes: Xanthoria parietina is characterized by its broad-lobed, non-sorediate thallus with frequent apothecia and ellipsoid conidia. Xanthoria elegans, which is also a comparatively large, apotheciate, and non-sorediate taxon, has narrower, convex lobes, which are tightly adnate and difficult to remove from the substrate. See also notes for that taxon.