Thallus: foliose, medium to large, 5-15 cm in diam., adnate lobes: +flattened and elongate (1-2 cm wide and up to 4 cm long); tips: rounded to subtruncate, often ascending and undulate upper surface: gray or blue-gray to brown when dry, blackish green when wet, tomentose or glabrescent centrally, dull to somewhat shiny, marginally and laminally phyllidiate phyllidia: squamulose medulla: white, with +loosely interwoven hyphae photobiont: Nostoc lower surface: white, with anastomosing pale, smooth, flattened veins, rhizinate rhizines: white, darkening, bushy or penicillately branched Apothecia: +round to oblong, becoming saddle-shaped, semi-immersed on short, ascending lobes, up to 5 mm in diam.; margin: smooth to crenulate disc: flat, dark brown to black, smooth ascospores: colorless to pale brown, acicular, 3(-5) septate, 30-45 x 4-5 µm Pycnidia: not seen in Sonoran material Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: among mosses over soil World distribution: Central and South America Sonoran distribution: frequent in Arizona, southern California (Riverside), Chihuahua, and Baja California Sur, at mid- and higher elevations. Notes: Peltigera fibrilloides is a poorly known taxon and additional studies are needed to clarify its relationship to P. praetextata and other phyllidiate, tomentose taxa. Their morphological differences, mainly the shape and branching pattern of rhizines, are small and liable to be influenced by environmental factors and age of thalli.