Thallus: crustose, continuous or verrucose-areolate; prothallus: not visible, or white areoles: flat or verrucose or verruculose, thin or thick, opaque, ecorticate surface: yellowish white to yellowish gray or whitish gray to gray, smooth or rough, epruinose, with an indistinct margin or arachnoid, esorediate Apothecia: sessile, 0.5-1.0(-1.6) mm in diam., lecanorine disc: red-brown, plane, epruinose margin: concolorous with thallus, thin, persistent, even, not flexuose, smooth, entire, without a parathecial ring amphithecium: present, with numerous algal cells, with numerous small crystals which dissolve in K, corticate; cortex: hyaline, distinct, basally thickened, gelatinous or interspersed, (15-)20-25(-30) µm thick laterally, (25-) 45-55(-60) µm thick basally parathecium: hyaline, containing crystals soluble in K epihymenium: red-brown to orange-brown, with pigment not dissolving in K, without crystals hymenium: clear; paraphyses: not thickened or slightly thickened apically, not pigmented or red-brown to orange-brown; subhymenium: hyaline, 15-20 µm thick; hypothecium: hyaline, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid or broadly ellipsoid, (10.5-)14.5-16.5(-17) x (5-)5.5-7(-8.5) µm; wall: less than 1 µm thick Pycnidia: not seen Spot tests: K+ yellow, C-, KC-, P- or P+ pale yellow Secondary metabolites: atranorin (major), chloroatranorin (minor) and unknown triterpenoids. Substrate and ecology: on soil or siliceous or calciferous rocks World distribution: in Mediterranean areas of the Northern Hemisphere, recorded from northern Africa, western Asia, western Europe, and southwestern North America Sonoran distribution: Arizona, southern California, Baja California Sur, Chihuahua, and Sonora. Notes: Lecanora campestris is characterized by the presence of small amphithecial crystals, the distinct amphithecial cortex, the clear red-brown epihymenium and the presence of triterpenoids in addition to the atranorin chemosyndrome. The species is often confused with morphologically similar, saxicolous Lecanora spp. (Brodo 1986, Lumbsch 1998), probably since it is a very common species in Europe and there is a tendency to use European names in early studies of extra-European taxa. Similar species that occur in the study area include L. galactiniza, L. pseudistera and L. subimmergens. All three species, however, differ in having large amphithecial crystals and also have a different chemsitry: L. galactiniza lacks triterpenoids, L. pseudistera contains the 2'-O-methylperlatolic acid chemosyndrome, and L. subimmergens contains zeorin.