PetasitesMill. (Asteraceae: Senecioneae) is a taxonomically difficult genus of polygamodioecious, perennial clonal herbs distributed across Canada, Alaska, and the northern contiguous United States. The taxonomic confusion surrounding the genus is reflected in the ambiguity of the various classification systems currently used. As many as ten species and as few as two species have been recognized (Petasites sagittatus(Banks ex Pursh) Gray andPetasites frigidus(L.) Fries with three varieties), in addition to one hybrid taxon. To determine if discrete groups could be recognized according to a combination of vegetative and (or) reproductive characters and thereby clarify the phenetic relationships among the taxa ofPetasites, morphological data were subjected to principal components and discriminant analyses. Particular emphasis was placed onP. frigidusvar.frigidus,P. frigidusvar.nivalissensu Bogle, and the purported hybrid between these taxa, which exhibits an intermediate morphology (thefrigiduscomplex). Additionally, the specific status ofP. sagittatuswas investigated. Evidence obtained from multivariate morphometric analyses indicates that North AmericanPetasitesis comprised of four closely related polymorphic entities. While morphological variation among different taxa ofPetasitesis continuous for most reproductive characters, leaf characters were determined to be the most taxonomically discriminating. The entities of thefrigiduscomplex form a cohesive group somewhat distinct from the other taxa. The morphological differentiation betweenP. sagittatusand other taxa ofPetasitesis not considered sufficient to warrant recognition of specific status. Therefore, we recommend that only one polymorphic species ofPetasitesin North America be recognized (P. frigiduswith three varieties) in addition to one hybrid taxon originating from a cross between two of the varieties.Key words:Petasites, Asteraceae, North America, systematics, principal components analysis, discriminant analysis.