Thallus: placodioid, rosettiform, bullate-areolate to verrucose, or sometimes areolate-squamulose, (1-)3-5 cm wide, coalescing, rather tightly appressed, 1-2 mm thick; prothallus: absent, or vestigial and greenish black lobes: distinct, radiating, 1-1.5 mm long, 0.5-1 mm wide, plane to convex, smooth, becoming wrinkled and cracked towards thallus center upper surface: grayish green-yellow to light or pale greenish yellow or light yellow (turning grayish yellow to moderate yellow or yellow-brown in herbarium), smooth, +shiny, slightly cracked in places, lacking soredia and thallospores upper cortex: composed of hyphae 3-7(-8) µm wide (in K) with elongated lumina 1.7-2 µm wide, with frequent dead algal cells, 60-80 µm thick; epinecral layer: 15-20 µm or more thick, becoming cracked as seen from above medulla: white, dense to moderately dense; hyphae: 3-4(-7) µm thick, thick-walled; algal layer: continuous to indistinctly columnar-divided with small hyphal bundles, 35-75 µm thick; algae: partly in clumps lower surface: pale to grayish yellow-brown, or green-black lower cortex: present near lobe tips, up to 25 µm thick, pale to dark brown or bluish green Apothecia: scattered to abundant, sessile to constricted sessile, formed submarginally one or few per areole, immersed in small verrucae, soon dilated and constricted at base, rounded to irregular or occasionally lobed when old, 0.6-1.5(-4) mm in diam. disc: red to blue, usually densely pruinose, appearing orangish, grayish, or greenish yellow, becoming epruinose and blue-black at higher elevations or latitudes, plane or slightly concave then weakly or rarely moderately convex margin: usually concolorous with or paler than thallus, entire to flexuous or shallowly crenate, usually persistent, raised then evenly high, 0.1-0.2 mm wide, without a parathecial ring but margin sometimes blackening immediately next to disc amphithecium: present, with a well developed algal layer (30-50 µm thick) upper, outer part of margin and extending intermittantly below the hypothecium, with grayish granules insoluble in K in the medulla, corticate; cortex: similar to that of thallus, 35-40 µm thick, up to 100 µm wide towards base parathecium: hyaline, 20-25 µm thick laterally epihymenium: not inspersed, on surface +coarsely granular (insoluble in K and N), 10-15 µm thick hymenium: hyaline, 50-60 µm tall; paraphyses: indistinct and conglutinate, 1.5-3 µm wide in K; tips: hyaline to later dark green, clavate to +capitate, 3-5 µm wide; subhymenium: hyaline or pale brown, 40-50(-80) µm thick, with oil droplets; hypothecium: with mostly randomly oriented hyphae 3(-7) µm wide and with elongated lumina 0.5 µm wide, 30-170(-250) µm thick asci: clavate to swollen-clavate, 8-spored ascospores: hyaline, simple, ellipsoid to broadly ellipsoid, 8-10.5 x 5.5-7.5 µm Pycnidia: frequent, immersed; ostiole: pale to dark blue-green; conidiophores: type III of Vobis (1980) conidia: filiform, usually bent or curved, (20-)25-35 µm long Spot tests: cortex K+ pale yellow or K-, C- or + yellow, KC+ yellow; medulla K-, C+ red, or C- (or yellow), P+ yellow or P-, occasionally P+ yellow and C+ red simultaneously; blackened parts including paraphyses tips K+ green, N+ red-violet Secondary metabolites: cortex with usnic acid; medulla with psoromic acid +conpsoromic and hypopsoromic acids, or lecanoric acids, less often both psoromic and lecanoric acids, occasionally with unknowns. Substrate and ecology: on hard, usually non-calcareous rocks, 1200-4100 m, from semi-arid steppe-desert to juniper or oak woodlands, to mesic riparian to alpine areas World distribution: western North America Sonoran distribution: .Arizona at 1000-3600 m, Southern California, Baja California, and Chihuahua at 1600 m. Notes: Forms of L. novomexicana found at higher elevations ("L. thomsonii") differ from the typical form in having the thallus yellower, lobes more convex, and disc becoming bluish black and epruinose. Lecanora novomexicana might be confused with memebers of the L. bipruinosa group which grows in warmer (usually lower elevation) habitats, and never occur at the same sites. Lecanora novomexicana differs by the almost complete lack of thallus pruina (characteristic of L. bipruinosa) and the thallospores (characteristic of L. nashii).