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 (disintegrating into irregular groups of lobes with age), large, 10-20 cm in diam., adnate lobes: +flattened and elongate (2-4 cm wide and up to 10 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 when wet, smooth, dull to somewhat shiny, occasionally somewhat scabrose, rarely pruinose marginally, without isidia; marginally sorediate soredia: pale gray to bluish tinged, coarsely granular medulla: white, +loosely interwoven hyphae photobiont: Nostoc lower surface: pale near margin, with anastomosing pale, smooth, flattened and reticulate veins, rhizinate rhizines: brown to black, fasciculate, little branched, at base of the lobes Apothecia: +round to oblong, becoming saddle-shaped, on short, ascending lobes, up to 9 mm in diam.; margin: smooth to crenulate disc: flat, dark brown to black, smooth ascospores: colorless to pale brown, acicular, 3(-5) septate, 50-90 x 3-5 µm Spot tests: all negative Secondary metabolites: tenuiorin, methyl gyrophate, gyrophoric acid, + 7α-acetoxyhopan-22-ol, hopane-15α-acetoxyhopan-22-ol, hopane-6 α,22-diol and unidentified terpenoids. Substrate and ecology: among mosses over soil World distribution: temperate and boreal regions of North America, Europe and Asia Sonoran distribution: rare at mid-elevations in southeastern Arizona. Notes: Only one collection was tentatively identified to P. neopolydactyla and further investigation is required to settle the problems in P. polydactylon group. Coarse thalli and dark little-branched, slender fasciculate rhizines are diagnostic of the specimen in contrast to P. polydactylon, but these characters are similar to those of P. dolichorhiza (Nyl.) Nyl., a species found farther southward in Mexico. The occurrence of P. occidentalis (E. Dahl) Kristinsson - with thick thallus which is often greenish when wet and has a centrally black lower surface and dark bushy rhizines - might also be possible at higher altitudes, but the relationships in this complex are not yet well understood.