Phylogeny and subgeneric classification of Bouteloua with a new species, B. herrera-arrietae (Poaceae: Chloridoideae: Cynodonteae: Boutelouinae)

Bouteloua (Poaceae: Chloridoideae: Cynodonteae; Boutelouiane) is an important genus of forage grasses containing 60 species found primarily in the Americas with a center of diversity in northern Mexico. A modern subgeneric classification is lacking. The goals of our study were to reconstruct the evolutionary history among the species of Bouteloua using molecular data with increased species sampling compared to previous studies. A phylogenetic analysis was conducted on 209 samples, of which 59 species (206 individuals) were in Bouteloua, using two plastid (rpl32-trnL spacer and rps16-trnK spacer) and nuclear ITS 1&2 (ribosomal internal transcribed spacer) sequences to infer evolutionary relationships and produce a subgeneric classification. Overall, ITS and plastid phylogenies rendered similar patterns. However, the ITS phylogeny lacked backbone structure, recovering only four internal clades out of nine found in the plastid phylogeny. The ITS network shows a radiative evolutionary pattern and indicates a number of incompatible splits, suggesting past hybridization between species of different sections. The maximum-likelihood tree from the combined plastid and ITS regions is well resolved and depicts a strongly supported monophyletic Bouteloua that includes ten strongly supported clades and one moderately supported clade. The molecular results support the recognition of 10 sections and two subsections within Bouteloua s.l.; three sections are new: Barbata, Hirsuta, and Trifida; four sections are new combinations: Buchloe, Cyclostachya, Opizia, and Triplathera; and two subsections are new: Eriopoda and Hirsuta. Based on our molecular results and the possession of unique morphological characters we describe a new species from Nuevo León, Bouteloua herrera-arrietae.