Tragopogon pratensis: Multiple introductions to North America, circumscription, and the formation of the allotetraploid T. miscellus

Abstract

Tragopogon (Asteraceae) includes two recently and repeatedly formed allopolyploids, T. mirus and T. miscellus, both of which formed in western North America following the human-mediated introduction of three diploids from Europe: T. dubius, T. porrifolius, and T. pratensis. We recently investigated the genetics of the introduction history to North America of T. dubius, the shared parent of both allopolyploids. Here, we investigate the introduction of T. pratensis into North America, the second diploid parent of T. miscellus. Using ITS sequence data, we found that T. pratensis as currently defined in the narrow sense is polyphyletic and comprises at least four different major ITS types in its native range. Of these native range ITS patterns, two have been introduced from Europe into North America and now occur widely across Canada and the U.S.A. Although the allotetraploid T. miscellus formed multiple times in western North Amer- ica, only one of these ITS types was involved in the recurrent formations. These results for T. pratensis parallel our findings for T. dubius and further suggest that not all genotypes of these two species may be able to participate in the formation of allopolyploids. Our phylo- genetic analyses reveal that several entities traditionally considered part of T. pratensis in the narrow sense are genetically distinct and mark unique lineages that may ultimately merit recognition as separate species. This proclivity for genetically distinct entities (potential cryptic species) within species recognized based on morphology appears common in Tragopogon. To unravel the complexities of what is referred to as “T. pratensis”, more intensive phylogenetic analyses involving many more samples from across the geographic range of the species are required, as are detailed assessments of taxonomy, morphology, and cytology.