Thallus: verrucose-areolate or dispersed areolate, flat or verrucose or verruculose, thin, ecorticate; prothallus: not visible, or white surface: yellowish white to yellowish gray or whitish gray to gray, opaque, smooth or rough, with an indistict margin, epruinose or slightly pruinose, esorediate Apothecia: sessile or adnate or constricted at the base to almost subpedicilate, lecanorine, 0.6-1.3 mm in diam. disc: bright red-brown to orange-brown or gray-brown, plane, slightly to heavily pruinose; pruina: bluish gray to bright gray or whitish gray margin: concolorous with thallus, thin or thick, persistent, even or prominent, not flexuose, smooth or rough, entire or verrucose or verruculose or crenulate, without a parathecial crown amphithecium: present, pulicaris-type, with large crystals insoluble in K, but small crystals present which dissolve rapidly in K, with numerous algal cells, corticate; cortex: eucortical, distinct, basally thickened, gelatinous, interspersed, hyaline, (13-)15-25(-27) µm thick laterally, 20-55 µm thick basally parathecium: hyaline, lacking crystals, 10-15 µm thick epihymenium: red-brown to orange-brown or brown to dark brown, chlarotera-type, with crystals dissolving in K, with pigment dissolving in K, 10-15 µm thick hymenium: hyaline, 20-25 µm tall; paraphyses: hyaline below, reddish brown apically, with slightly thickened tips, up to 2.5 µm; subhymenium: hyaline; hypothecium: hyaline, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid or broadly ellipsoid, (11-)11.5-14.5(-15) x (5-)6-7.5(-8) µm; wall: less than 1 µm thick Pycnidia: not seen Spot tests: K+ yellow, C-, KC-, P+ pale yellow Secondary metabolites: atranorin, usnic acid, and zeorin. Substrate and ecology: bark, or wood World distribution: Asia, Australasia, central and northwestern Mexico Sonoran distribution: western Chihuahua. Notes: A detailed discussion of this species is given by Lumbsch (1994). Lecanora flavidomarginata is characterized by the bluish to whitish gray pruinose discs and the broadly ellipsoid spores. None of the other species treated by Lumbsch et al. (1995) is morphologically similar. For comparison with L. casuarinophila, see under that species. Another similar species is L. orizabana, which lacks usnic acid and depsides, and has a continuous to rimose or verrucose-areolate thallus and the amphithecial cortex 75-150 µm thick basally.