The genus Xanthoria (Fr.) Th.Fr. in North America

The lichenized ascomycete genus Xanthoria (Fr.) Th.Fr. (Teloschistaceae) in continental United States and Canada is revised. The following 15 species are recognized: Xanthoria borealis, X. candelaria, X. concinna, X. elegans, X. fallax, X. fulva, X. hasseana, X. mendozae, X. montana, X. oregana, X. parietina, X. polycarpa, X. sorediata, X. tenax, and X. ulophyllodes. The morphology, anatomy, secondary chemistry, ecology, and distribution of these species is discussed. A key for the identification of the species is presented together with distribution maps and illustrations of all species. Two taxa are described as new: Xanthoria montana and X. tenax. In addition to the newly described species, X. concinna and X. mendozae are reported for the first time from the study area. A number of taxa are reduced into synonymy and all names treated are typified