surface: yellowish gray to yellowish white, flat to verrucose, glossy, epruinose, with a distinct margin, esorediate; Apothecia: sessile, 0.7-1.4 mm in diam., lecanorine disc: dark red-brown to gray-brown, epruinose margin: prominent, entire, verruculose, without a parathecial ring amphithecium: present, with numerous algal cells, with small and large crystals, small crystals dissolving in K but large crystals insoluble in K, corticate; cortex: hyaline, indistinct, interspersed, basally not thickened, 15-25 µm thick parathecium: hyaline, without crystals, 15-20 µm thick; algal cells: numerous epihymenium: red-brown to brown, pigmentation not altered by K, without crystals hymenium: hyaline, clear; paraphyses: slightly thickened (up to 3.5 µm wide) apically; subhymenium: hyaline, 15-20 µm thick; hypothecium: upper part hyaline, lower part reddish brown, without oil droplets asci: clavate, 8sproed ascospores: hyaline, simple, ellipsoid to narrowly ellipsoid, (9-)10-12.5(-14.5) x 4.5-6.5 µm Pycnidia: not seen in North American material, but according to Vänskä (1986) they are immersed in the thallus conidia: filiform, straight or curved, 13-18 x 0.5 µm Spot test: thallus and apothecial margin K+ yellow, C-, KC-, P+ yellowish orange Secondary metabolites: atranorin (major), 6α acetoxyhopane-16α,22-diol (minor), chloroatranorin (minor), dehydroconstipatic acid (minor), epanorin (minor), lichesterinic acid (major), protodehydroconstipatic acid (minor), protolichesterinic acid (major), zeorin (major); and an unknown secalonic acid derivative. Substrate and ecology: on exposed siliceous rocks World distribution: restricted to the neotropics Sonoran distribution: Chihuahua. Notes: Lecanora vainoi is characterized by a pigmented hypothecium, egranulose epihymenium, narrow ascospores, and the presence of several aliphatic acids. A superficially similar species is L. kalbiana, currently only known from Brazil, which differs in containing the chodatin chemosyndrome and having broader ascospores. None of the other Lecanora spp. occurring in the Sonoran Desert region are similar to that quite distinctive species. This is the first record of L. vainoi from North America.