Substrate and ecology: open desert with Canotia, or with Larrea and Opuntia or in pine-oak forests Sonoran distribution: Arizona, 450-1700(-2300) m, Sonora, 450-1370 m. Notes: Lecanora valesciaca is distinguished from pruinose modifications of L. muralis especially by having a closely adnate and completely pruinose thallus, rather weakly separated lobes, and lacking triterpenes. The thallus anatomy of the two species is also quite different: in L. valesiaca the cortex lacks conical hyphal bundles and is densely inspersed with grayish granules, and the medulla is solid and dense. Forms of L. valesiaca with green discs and short lobes, and more typical forms with yellow-brown discs and long lobes, both occur at Pena Blanca Lake, Arizona, and appear to intergrade with each other. In our region, the thalli of many specimens with greenish discs are smaller (mostly to 0.5-1 cm diam.) and shorter lobed than normal and are + completely covered by apothecia; collections from eastern Eurasia having greenish discs were regarded by Poelt (1958) as a distinct variety (var. Poelt). The division of the hypothecium into two layers, and the distinctness of the subhymenium, are unusual features of L. valesiaca. For comparison of L. valesiaca with similar species (e.g., L. arenisaxicola) see under those species.