Hybrid genera in Liatrinae (Asteraceae: Eupatorieae)

Liatrinae is a small subtribe of Eupatorieae that occurs in North America with a center of generic-level diversity in the southeastern United States. Molecular phylogenetic data were sought to assess whether two monotypic genera, Garberia and Hartwrightia, are accurately placed in the subtribe, and to resolve questions of the generic-level classification of Carphephorus. Phylogenetic analyses of nuclear ITS/ETS and plastid DNA data indicated that Garberia is the basalmost diverging lineage, and that Hartwrightia is phylogenetically embedded in the subtribe. There was significant incongruence between the ITS/ETS and plastid DNA datasets in the placement of Hartwrightia and another monotypic genus, Litrisa, suggesting that both are of original hybrid origin. The results also showed that Carphephorus s.l. is not monophyletic, and even after removal of the two species of Trilisa, it is still paraphyletic to Liatris. The apparent hybrid origin of Hartwrightia, which is morphologically transgressive relative to its inferred parental lineages, suggests that reticulation between phylogenetically distinct lineages may be a recurrent problem for phylogenetic estimation in Asteraceae.

Research highlights► Liatrinae are monophyletic with inclusion of Garberia and Hartwrightia. ► Liatris and Trilisa are monophyletic, but Carphephorus is paraphyletic. ► Incongruence in ITS/ETS and plastid DNA results suggests phylogenetic reticulation. ► Hartwrightia and Litrisa are genera of apparent hybrid origin. ► Hartwrightia is morphologically transgressive compared to its inferred parental lineages.