Thallus: crustose, verrucose-areolate, verrucose or verruculose; prothallus: not visible areoles: thin, opaque or glossy, ecorticate surface: yellowish white to yellowish gray or pale green to greenish white, smooth, epruinose, with an indistinct margin, esorediate Apothecia: sessile, 0.4-1 mm in diam., lecanorine disc: red-brown or brown or dark brown to blackish brown, plane, epruinose margin: concolorous with thallus, thin, persistent, even or prominent, not flexuose, smooth, entire, without a parathecial ring amphithecium: present, with numerous algal cells, with large and small crystals, the small ones soluble in K, corticate; cortex: hyaline, indistinct, basally not thickened, interspersed, 10-20 µm thick laterally, 10-20 µm thick basally parathecium: hyaline, containing crystals insoluble in K epihymenium: red-brown to orange-brown, with pigment dissolving in K, with crystals dissolving in K hymenium: hyaline, clear; paraphyses: not thickened (up to 2.5 µm wide) apically, not pigmented; subhymenium: hyaline, 15-20 µm thick; hypothecium: hyaline, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid or broadly ellipsoid, (11-)11.5-16.5(-17) x (5.5-)6.5-7.5(-8) µm; wall: less than 1 µm thick Pycnidia: not seen Spot tests: K+ yellow, C+ orange to orange-red, P- or P+ pale yellow Secondary metabolites: arthothelin (major or minor), atranorin (minor), chloroatranoin (trace), usnic acid (major), and zeorin (major). Substrate and ecology: on bark of deciduous trees and shrubs World distribution: pantropical, recorded from Australasia, North America, and the Pacific Area Sonoran distribution: Baja California Sur. Notes: Lecanora flavidofusca is readily distinguished by its relatively dark brown apothecial discs, granulose epihymenium, and the presence of usnic acid. It is closely related to L. alba, which, however, can be distinguished by the egranulose epihymenium, and smaller ascospores. The saxicolous L. pseudogangaleoides resembles L. flavidofusca in having dark apothecial discs, but differs in the epihymenium type and by having a different chemistry (containing gangaleoidin). This is the first record of this species for North America.