sp. nov. Diagnosis: Thallus foliosus, sorediis isidiisque destitutus; subtus albus vel pallido-brunnescens; ascosporae 19-28 x 7-10 µm. Thallus: foliose, up to 7 cm in diam., usually +orbicular lobes: elongate and discrete to somewhat irregularly flabellate, truncate or more rounded-crenate, 0.5-1(-2) mm broad, usually +flat or slightly concave, prostrate upper surface: pale gray to brownish gray, epruinose but with an inconspicuous, patchy, pruina-like epinecral layer over much of the upper surface, without soredia or isidia upper cortex: paraplectenchymatous medulla: white lower cortex: paraplectenchymatous lower surface: white to pale tan, dull; rhizines: simple, concolorous with the lower surface or darkening, often rather sparse Apothecia: frequent, up to 2 mm in diam., sessile to short stipitate; margin: entire or becoming crenate or crenate-lobulate with age; corona of rhizines: absent or inconspicuous ascospores: narrowly ellipsoid, 19-25(-28) x 7-10 µm, Physcia-type Spot tests: all negative in cortex and medulla Secondary metabolites: none detected. Substrate and ecology: bark or rock World distribution: North America Sonoran distribution: Sonora.. Notes: Among sympatric species, only Physciella nepalensis is likely to be confused with P. sonorae. That superficially similar species can be distinguished by the lack of a pruina-like, epinecral layer and by its clearly prosoplectenchymatous lower cortex. Within Phaeophyscia, the only similar North American species is P. leana, an uncommon species apparently restricted to the east-central United States (Wilhelm et al. 2000). That species differs from P. sonorae by its longer, more strap-shaped lobes, lack of an epinecral layer, and slightly shorter ascospores (18-23 x 8-10.5 µm). Phaeophyscia sonorae is closely related to the sorediate species P. nashii.