Molecular phylogeny of the North American eurybioid asters (Asteraceae, Astereae) based on the nuclear ribosomal internal and external transcribed spacersThis paper is one of a selection of papers published in the Special Issue on Systematics Research.

The eurybioid asters Oreostemma , Herrickia , Eurybia , and Triniteurybia form a complex that is part of the North American clade of tribe Astereae. They comprise 31 species of perennial herbs that are widely distributed on the continent. Previous analyses had shown poor resolution among the four genera and among the species, particularly within Eurybia (23 spp.), which includes diploids and polyploids. We investigated phylogenetic relationships within the group using the nuclear ribosomal ITS and ETS regions, in separate and combined parsimony and Bayesian analyses. We detected incongruence between the ITS and ETS regions when polyploids were included, and so only diploids were considered in the combined analyses. Eurybia pygmaea (Lindl.) G.L. Nesom is confirmed as a member of Symphyotrichum ; Eurybia is monophyletic once this species is re-classified. The eurybioids form a paraphyletic grade with Oreostemma, sister to the remaining taxa, followed in succession by Herrickia , Eurybia , and Triniteurybia , and with the latter genus sister to subtribe Machaerantherinae. Thus the xeric Machaerantherinae (x = 6, 5, 4) is nested within the grade of mesic eurybioids (x = 9). Although largely grouping together, the polyploid taxa of Eurybia apparently do not constitute a clade and their relationships to the diploid taxa and to each other could not be assessed further. Among the diploids, two clades emerge: one including the western Eurybia integrifolia (Nutt.) G.L. Nesom and Eurybia sibirica (L.) G.L. Nesom, and the southeastern Eurybia eryngiifolia (Torr. & A. Gray) G.L. Nesom; and a second including the western Eurybia radulina (A. Gray) G.L. Nesom, the eastern cordate-leaved (sect. Eurybia) and the narrow-leaved, mostly coastal plain species of Eurybia. Our analyses, therefore, do not support the current classifications of Eurybia.