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The Lecanora novomexicana complex of lobate to areolate-squamulose taxa in sect. Petrasterion subsect. Pseudocorticatae Poelt is well represented in semi-arid temperate to alpine areas over much of western North America, and is characterized by usnic acid and fatty acids as constant major substances, and yellowish pruinose to blue-black discs. Parmularia novomexicana B. de Lesd. and L. thomsonii Magnusson are treated in this article as synonyms of L. novomexicana Magnusson. At least some of the considerable variability in L. novomexicana sensu lato correlates with environmental factors; psoromic acid is often absent at high elevations and latitudes and is mostly replaced by lecanoric acid at low elevations in the Southwest. Lecanora nigromarginata Magnusson, although frequently confused with Rhizoplaca melanophthalma (DC.) Leuck. & Poelt, is provisionally retained as a separate taxon. Lecanora novomexicana Magnusson is unrelated to its later homonym, L. novomexicana B. de Lesd.