A molecular phylogeny and classification of the Cynodonteae (Poaceae: Chloridoideae) with four new genera: Orthacanthus, Triplasiella, Tripogonella, and Zaqiqah; three new subtribes: Dactylocteniinae, Orininae, and Zaqiqahinae; and a subgeneric classification of Distichlis

摘要

Morphologically, the tribe Cynodonteae is a diverse group of grasses containing about 839 species in 96 genera and 18 subtribes, found primarily in Africa, Asia, Australia, and the Americas. Because the classification of these genera and species has been poorly understood, we conducted a phylogenetic analysis on 213 species (389 samples) in the Cynodonteae using sequence data from seven plastid regions (rps16-trnK spacer, rps16 intron, rpoC2, rp132-trnL spacer, ndhF, ndhA intron, ccsA) and the nuclear ribosomal internal transcribed spacer regions (ITS 1 & 2) to infer evolutionary relationships and refine the current classification. The phylogenetic tree from the combined plastid and nuclear region is well resolved depicting a strongly supported monophyletic Cynodonteae that includes 17 strongly supported clades corresponding to the subtribes Tripogoninae, Pappophorinae, Traginae, Muhlenbergiinae, Hilariinae, Scleropogoninae, Boutelouinae, Monanthochloinae, Dactylocteniinae, Eleusininae, Aeluropodinae, Triodiinae, Orcuttiinae, Zaqiqahinae, Farragininae, Perotidinae, and Gouiniinae, and two moderately supported clades corresponding to the Orininae and Hubbardochloinae. The plastid data places Odyssea paucinervis as sister to Neobouteloua in the Dactylocteniinae whereas the nuclear ITS data places it as sister to Aeluropus in the Aeluropodinae. Odyssea mucronata is strongly supported sister to the Cteniinae, Trichoneurinae, Farragininae, Perotidinae, Hubbardochloinae, and the Gouiniinae, and not closely related to Odyssea paucinervis. The nuclear data placed Acrachne racemosa as sister to Dactyloctenium in the Dactylocteniinae while the plastid data places it near the base of the Eleusininae. Our new classification recognizes three new subtribes (bringing the total to 21 subtribes): Dactylocteniinae that includes Acrachne, Brachychloa, Dactyloctenium, and Neobouteloua; Orininae with Cleistogenes and Orinus; and Zaqiqahinae with a single genus, Zaqiqah gen. nov.; Hubbardochloinae (resurrected here) with seven genera; and describes four new genera: Orthacanthus (Traginae) with a single species, Triplasiella (Gouiniinae) with a single species, Tripogonella (Tripogoninae) with three species, and Zaqiqah with a single species. We additionally provide a subgeneric classification of Distichlis recognizing three sections: D. sect. Monanthochloe, D. sect. Bajaenses, and D. sect. Spicatae, the latter two representing new sections. The following nine new combinations are made: Distichlis sect. Monanthochloe, Orthacanthus pedunculatus, Tridentopsis buckleyana, Tridentopsis mutica var. elongata, Triplasiella eragrotoides, Tripogonella loliiformis, Tripogonella minima, Tripogonella spicata, and Zaqiqah mucronata. We lectotypify the following five names: Festuca loliiformis, F. minima, F. mucronata, Triodia eragrostoides, and Uralepis elongata.