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

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 America, 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 phylogenetic 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.

Automated summary

Tragopogon (Asteraceae) is a genus that includes two recently formed allopolyploids, T. mirus and T. miscellus, in western North America. The introduction of diploid parents, T. dubius and T. porrifolius from Europe, played a role in the formation of these allopolyploids. In this study, we focused on the introduction of the second diploid parent, T. pratensis, into North America. Our findings show that T. pratensis as currently defined is polyphyletic, with at least four major ITS types in its native range. Two of these ITS types have been introduced from Europe into North America and are widespread in Canada and the U.S.A. The formation of T. miscellus in the western North America involved only one of these ITS types. Our research suggests that not all genotypes of T. pratensis may be capable of participating in the formation of allopolyploids. Additionally, we found that there are genetically distinct entities within T. pratensis that may be considered separate species. Further research involving phylogenetic analyses, taxonomy, morphology, and cytology are needed to fully understand the complexities of T. pratensis.