Thallus: crustose, dispersed-verrucose to verruculose; prothallus: white areoles: thin or thick, glossy, ecorticate surface: smooth, whitish gray to yellowish gray, epruinose, with an indistinct margin, esorediate Apothecia: sessile, 0.6-1.8 mm in diam., lecanorine disc: black to brown-black, even when wet, plane, epruinose margin: concolorous with thallus, inner part often black, thin or thick, persistent, prominent, smooth, entire or verruculose, without a parathecial ring amphithecium: present, with numerous algal cells, with large crystals insoluble in K, corticate; cortex: hyaline, distinct, uniform or basally thickened, gelatinous or sometimes not, interspersed with small crystals, 15-25 µm thick laterally, 25-50 µm thick basally parathecium: hyaline, containing crystals soluble in K epihymenium: brown to greenish black, not turning green in K, without crystals hymenium: hyaline, clear; paraphyses: not thickened or slightly thickened apically, olivaceous; subhymenium: hyaline, 15-20 µm thick; hypothecium: hyaline or yellow-green, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, broadly ellipsoid to subspherical, 9-15 x 5.5-8 µm; wall: less than 1 µm thick Pycnidia: not seen Spot tests: thallus and apothecial margin K+ yellow, C-, KC-, P+ pale orange Secondary metabolites: atranorin (major), chloroatranorin (minor), gangaleoidin (major), and norgangaleoidin (minor). Substrate and ecology: on exposed siliceous rocks in montane areas World distribution: circumboreal, known from Asia and North America Sonoran distribution: Arizona. Notes: Lecanora argentea is very rare in the study area and is only known from a single locality in Arizona (Apache Co.). Brodo (1984) mentioned an additional collection from high altitudes in nearby New Mexico. This saxicolous species is characterized by black apothecial discs and the presence of the gangaleoidin chemosyndrome. It is similar to L. gangaleoides but differs in having a different epihymenium (Lumbsch 1992).