Xanthocephalum, Gutierrezia, Greenella, Gymnosperma, Amphiachyris, and Thurovia have been variously treated with regard to their generic limits by several authors in the last 3 decades. The generic delimitation presented here is based on a thorough re-evaluation of all 26 known North American members of these genera. The data obtained in the study strongly support the following disposition of the taxa, which differs from all previous treatments. (x = 6), a genus of montane areas in western Mexico and the southwestern United States, contains five species (one with three varieties) and is more closely related to Grindelia and Olivaea than to Gutierrezia and its allies. Gutierrezia (x = 4) encompasses seventeen specific and infraspecific taxa in North America, including not only the eight taxa recognized for it by Solbrig, but also five taxa formerly of Xanthocephalum, and the genera Greenella and Thurovia (the last resulting in Gutierrezia triflora, comb. nov.). The genus thus constituted ranges from central Mexico north and west through the central and western United States to Saskatchewan. Amphiachyris (n = 4 or 5) with two grassland species of Texas and central United States, and the monotypic Gymnosperma (x = 8), which ranges from northern Guatemala to Texas and westward to Arizona, are closely allied to Gutierrezia. The taxonomic problem presented by the group of genera that unfortunately have been called the Xanthocephalum complex is one of generic rather than specific circumscription. The genera concerned, besides Xanthocephalum, are Amphiachyris, Amphipappus, Greenella, Gutierrezia, Gymnosperma, and Thurovia. Taxonomic histories have been provided by Solbrig (1960a, 1960b, 196 1a, 196 1b, 1966), Ruffin (1974), Porter (1943), and Lane (1979, 1980b). A very brief summary of the several evaluations is as follows. A number of workers, including Bentham (1873) and Gray (1852, 1853, 1880a, 1880b, 1883), recognized the affinity of most of these genera, but for the most part maintained them as distinct entities. Shinners (1950) united all except Amphipappus and Thurovia under Xanthocephalum. Solbrig (1960b) again segregated them, while Ruffin (1974, 1977a) recommended that Gutierrezia and Greenella be submerged in and that Amphiachyris, Amphipappus, Gymnosperma, and Thurovia be considered distinct. It might seem unnecessary to reconsider this taxonomic problem in view of the several treatments already in the literature. However, data that have accumulated even since the most recent of these suggest that such a reconsideration is in order. None of the previous studies included every species of each genus; further, the various authors changed only the taxonomic rankings of whole, historically constituted genera. I wished