Thallus: crustose, thin, continuous to dispersed-verrucose or verruculose, ecorticate; prothallus: not visible surface: yellowish white to whitish gray, epruinose, with an indistinct margin, esorediate Apothecia: sessile to constricted at the base, 0.3-1.0 mm diam., lecanorine disc: dark red-brown to blackish brown, not or slightly pruinose margin: concolorous with the thallus, thin, entire, verrucose to verruculose, without a parathecial ring amphithecium: present, with numerous algal cells, with large crystals insoluble in K, corticate; cortex: hyaline, interspersed, uniform, c. 20 µm thick laterally and 20-25 µm thick basally parathecium: hyaline, 10-15 µm thick, with numerous small crystals soluble in K epihymenium: red-brown, with numerous crystals, pigmentation rapidly soluble in K hymenium: clear, hyaline; paraphyses: sparingly branched and slightly thickened (up to 2 µm wide) apically; subhymenium: hyaline, 15-20 µm thick; hypothecium: hyaline, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid to broadly ellipsoid, 8.5-12.5 x 5.5-8.5 µm Pycnidia: not seen Spot test: thallus and apothecial margin K+ yellow, C-, KC-, P+ pale orange Secondary metabolites: atranorin (major), chloroatranorin (minor), 4-dechlorogangaleoidin (minor), gangaleoidin (major) and norgangaleoidin (minor). Substrate and ecology: on bark of deciduous trees World distribution: probably pantropical, known from North and South America, and Australasia Sonoran distribution: southern California and Chihuahua. Notes: Lecanora pseudargentata is characterized by red-brown to dark brown apothecial discs, a granulose epihymenium, and the presence of the gangaleoidin chemosyndrome. Morphologically it is similar to L. argentata, but thas species differs in having an egranulose epihymenium and larger discs. Lecanora tropica is also similar and is readily distinguished by its egranulose epihymenium and the presence of the chodatin chemosyndrome.