Thallus: crustose, continuous or verrucose-areolate or dispersed-areolate or rugose; prothallus: not visible, or white areoles: flat or verrucose or verruculose, thin, opaque, ecorticate surface: yellowish white to yellowish gray or yellowish brown or orange-gray to brown-gray, smooth or rough, epruinose or slightly pruinose, with an indistinct, zonnate or fimbriate margin, esorediate Apothecia: subimmersed when young, sessile when mature or sessile, 0.3-1 mm in diam., lecanorine disc: orange-brown or yellowish brown, plane, epruinose or slightly whitish gray pruinose margin: concolorous with thallus, thin or thick, persistent, even, not flexuose, smooth, entire or verrucose or verruculose, without a parathecial ring amphithecium: present, with numerous algal cells, with large crystals insoluble in K, corticate; cortex: hyaline, indistinct, basally not thickened, gelatinous or interspersed, (15-)20-25(-30) Ám thick laterally, (15-)20-25(-30) Ám thick basally parathecium: hyaline, containing crystals soluble in K epihymenium: red-brown to orange-brown, with pigment dissolving in K, with crystals dissolving in K hymenium: hyaline, clear; paraphyses: slightly thickened (up to 2.5 Ám wide) apically, not pigmented; subhymenium: hyaline, 15-20 Ám thick; hypothecium: hyaline, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, 8-11 x (4-)5.2-6.5(-7) Ám; wall: less than 1 Ám thick Pycnidia: immersed, cerebriform; conidiophores: type II sensu Vobis conidia: filiform, 14-17 Ám long Spot test: thallus and apothecial margin K+ yellow, C-, KC-, P+ pale orange Secondary metabolites: containing atranorin (major), chloroatranorin (minor), 2'-O-methylisohyperlatolic acid (minor), 2'-O-methylperlatolic acid (major) and 2'-O-methylsuperlatolic acid (minor). Substrate and ecology: widely distributed on exposed siliceous rocks World distribution: pantropical known from southern Africa, Australasia, North and South America Sonoran distribution: Arizona, southern California, Baja California Sur, Chihuahua, Sinaloa, and Sonora. Notes: Lecanora plumosa is characterized by the orange-brown apothecial disc with a granulose epihymenium, relatively small ascospores, and the presence of the 2'-O-methylperlatolic acid chemosyndrome. Morphologically similar is L. neosonorensis, the difference of these two species are discussed under the latter. Another similar species is L. sulfurescens, which is readily distinguished by small granuels in the epihymenium, larger ascospores, and the presence of the gangaleoidin chemosyndrome and lack of depsides.