The Lecanora dispersa group in North America is revised based on about 1900 specimens from 25 herbaria. The following 19 species are recognized in the study area: Lecanora agardhiana Ach., L. albescens (Hoffm.) Florke, L. cf. andrewii B. de Lesd., L. crenulata Hook., L. dispersa (Pers.) Sommerf., L. flowersiana H. Magn., L. fugiens Nyl., L. hagenii (Ach.) Ach., L. invadens H. Magn., L. juniperina Sliwa, L. percrenata H. Magn., L. perpruinosa Froberg, L. persimilis (Th. Fr.) Nyl., L. salina H. Magn., L. sambuci (Pers.) Nyl., L. semipallida H. Magn., L. torrida Vain., L. wetmorei Sliwa, and L. zosterae (Ach.) Nyl.
The morphology, anatomy, lichen products, and ecology of the species are discussed. Based on the combinations of morphological, anatomical and chemical characters, four distinctive subgroups of species are identified: L. dispersa s.str. gr., L. semipallida gr., L. crenulata gr., and L. hagenii gr.
A key for the identification of the species is provided, and all species are illustrated. The North American species have varied distribution patterns, which are illustrated on maps. The taxa differ also in frequency: common species including L. dispersa, L. semipallida and L. hagenii; frequent species but with limited distributional ranges such as L. flowersiana, L. wetmorei, and L. zosterae; relatively rare species including L. albescens, and L. fugiens; and taxa known only from a single locality, such as L. agardhiana, L. perpruinosa, and L. salina. Seven of the species are reported for the first time from the continent: L. agardhiana, L. cf. andrewii, L. fugiens, L. invadens, L. percrenata, L. perpruinosa, and L. semipallida. Nomenclatural and taxonomic clarifications include the typification of L.
crenulata, L. persimilis, and L. sambuci, and the synonymy of L. turbinata Poelt & Leuckert with L. zosterae var. beringii. Two new combinations are made: L. zosterae var. beringii (Nyl.) Sliwa comb. nov. (= L. beringii) and L. zosterae var. palanderi (Vain.) Sliwa comb. nov. (= L. palanderi). Moreover, Lecanora
elenkinii Mereschk., L. flotoviana Spreng., L. thallophila H. Magn., and L. utahensis H. Magn., which at first were considered members of the group, were excluded from the study as they proved not to be related.