Thallus: tightly adnate to adnate, foliose, 2-10 cm in diam., irregularly branched, lobate lobes: narrow, sublinear to subirregular, elongate, contiguous to imbricate, plane to convex, 1.5-4 mm wide, lobe tips subrotund, ciliate, cilia simple, up to 0.15 mm long upper surface: whitish gray to pale greenish gray, smooth but cracked with age, dull, sometimes partly pruinose, usually strongly white maculate peripherally, becoming rugulose; soredia, isidia and pustulae absent medulla: white lower surface: black, densely rhizinate; rhizines: black, simple to very rarely squarrose Apothecia: numerous, laminal, 1.5-5 mm diam.; margin: smooth; disc: brown, imperforate ascospores: simple, broadly ellipsoid, 6-12 x 5-9 µm Pycnidia: common, laminal, immersed conidia: bacilliform, 6-8 x 1 µm Spot tests: cortex K+ yellow, C-, KC-, P+ yellow; medulla K-, C+ red, KC+ red, P- Secondary metabolites: upper cortex with atranorin and chloroatranorin; medulla with lecanoric acid (major). Substrate and ecology: frequent on bark in oak woodlands, rare on rock World distribution: pantemperate region, particularly those with Mediterranean climates, in North Ameica, Europe; Asia and Australasia Sonoran distribution: common in southern California and Guadalupe Island, Baja California.