Lessons from Plectocephalus (Compositae Cardueae-Centaureinae): ITS disorientation in annuals and Beringian dispersal as revealed by molecular analyses

摘要

Background and AimsThe geographic distribution of the genus Plectocephalus comprises a single species in Ethiopia, two in North America and possibly four more in South America, in a striking disjunction that is exceptional for genera of the tribe Cardueae. The enormity of this disjunction cast doubts on the precise taxonomic delineation of the genus, which is not unanimously recognized as a natural entity. The aims of this study were to define the generic boundaries of Plectocephalus and to formulate a hypothesis that would explain its natural range.