Thallus: foliose, approximately circular in outline (disintegrating into irregular groups of lobes with age), large, 515 cm in diam., thin, adnate lobes: +flattened and elongate (1-2 cm wide and up to 4 cm long), often dichotomously branched, imbricate or separate; tips: rounded to subtruncate, often ascending and undulate upper surface: gray or blue-gray to brown when dry, bluish gray or blackish green when wet, tomentose, without isidia and soredia medulla: white, with +loosely interwoven hyphae photobiont: Nostoc lower surface: white, with anastomosing pale, narrow and raised veins, rhizinate rhizines: white to pale brown, simple or squarrosely branched, scattered, Apothecia: +round to oblong, becoming saddle-shaped, semi-immersed on short, ascending lobes, up to 6 mm in diam.; margin: smooth to crenulate disc: flat, dark brown to black, smooth ascospores: colorless to pale brown, acicular, 3(-5) septate, 55-65 x 3-5 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: among mosses over soil, rock and tree trunks World distribution: temperate and boreal regions of North America, Europe and Asia Sonoran distribution: rare in California and Arizona. Note: Its narrow, raised and pale veins, its slender, little ramified rhizines and its thin, flexuose thalli characterize P. membranacea, which seems rare in the area. Peltigera canina, another non-phyllidiate, coarse species has not been recorded reliably from the area, but might be found at higher elevated mountain sites. Its veining pattern is flatter and darker and the bushy rhizines usually form confluent mats.