Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: foliose, approximately circular in outline, medium to large, 5-15 cm in diam. lobes: +flattened and elongate (up to 10 mm wide and up to 5 cm long), often dichotomously branched, slightly imbricate or separate; tips: rounded, often ascending and recurved upper surface: grayish brown to brown when dry, blackish green when wet, smooth, dull, thickly white-gray tomentose, especially towards margins, +white pruinose or frosted in older parts, without isidia or soredia medulla: white, with +loosely interwoven hyphae photobiont: Nostoc lower surface: pale brown to cream-colored, with anastomosing brown veins (pale peripherally, dark centrally), rhizinate rhizines: brown, dense, fasciculate, at base of the lobes Apothecia: frequent, oblong, saddle-shaped, on upper surface of the recurved lobe tips, up to 5 mm in diam. disc: recurved, red-brown to black, smooth ascospores: colorless to pale brown, very narrowly fusiform to acicular, 3-5(-6) septate, 30-70 x 3-5 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: among mosses or on bare soil at intermediate to relatively high elevations World distribution: temperate and boreal regions of North America, Europe, Asia, Australia and South America Sonoran distribution: the most common Peltigera in the region, in Arizona, southern California, Baja California, Sinaloa and Chihuahua. Notes: Its upward turned lobe margins, its branched and soon blackened, often confluent rhizines and its dark veins mostly separate P. rufescens from its tomentose allies. However, some populations tend to produce small lobes like phyllidia, so that these specimens are reminescent of P. fibrilloides.