A molecular phylogeny and classification of the Eleusininae with a new genus, Micrachne (Poaceae: Chloridoideae: Cynodonteae)

Abstract

The subtribe Eleusininae (Poaceae: Chloridoideae: Cynodonteae) is a diverse group containing about 212 species in 31 genera found primarily in low latitudes in Africa, Asia, Australia, and the Americas, and the classification among these genera and species is poorly understood. Therefore, we investigated the following 28 Eleusininae genera: Acrachne, Afrotrichloris, Apochiton, Astrebla, Austrochloris, Brachyachne, Chloris, Chrysochloa, Coelachyrum, Cynodon, Daknopholis, Dinebra, Diplachne, Disakisperma, Eleusine, Enteropogon, Eustachys, Harpochloa, Leptochloa, Lepturus, Lintonia, Microchloa, Ochthochloa, Oxychloris, Saugetia, Schoenefeldia, Stapfochloa, and Tetrapogon. The goals of our study were to reconstruct the evolutionary history of the subtribe Eleusininae using molecular data with increased species sampling compared to earlier studies. A phylogenetic analysis was conducted on 402 samples, of which 148 species (342 individuals) were in the Eleusininae, using four plastid (rpl32-trnL spacer, ndhA intron, rps16-trnK spacer, rps16 intron) and nuclear ITS 1 & 2 (ribosomal internal transcribed spacer) sequences to infer evolutionary relationships and revise the classification. We found strong support for the following Eleusininae lineages: Acrachne, Apochiton, Astrebla, Austrochloris, Chloris, Chrysochloa, Cynodon, Daknopholis, Dinebra, Diplachne, Disakisperma, Eleusine, Enteropogon, Eustachys, Leptochloa, Lepturus, Micrachne gen. nov., Stapfochloa, and Tetrapogon, and moderate support for Harpochloa and Microchloa. Four species of Brachyachne, including the type, are imbedded within Cynodon; Oxychloris scariosa (monotypic) is sister to Harpochloa-Microchloa; Coelachyrum is polyphyletic since C. lagopoides, Apochiton burttii, and C. poiflorum form a grade, with the latter species sister to Eleusine; Schoenefeldia appears paraphyletic since Afrotrichloris martinii and Schoenefeldia transiens together are sister to Schoenefeldia gracilis; Saugetia fasciculata, Enteropogon brandegeei, and E. chlorideus are embedded within Tetrapogon; Lintonia nutans and Ochthochloa compressa are embedded in Chloris; and Enteropogon mollis and Chloris exilis are embedded in Leptochloa. Our plastid and ITS analyses show rearrangement of lineages within Acrachne and Chloris, indicating possible hybridization events or evidence for multiple origins. The molecular results support recognition of a new genus, Micrachne with five species and emendation of Stapfochloa with six species. We provide 22 new combinations, Chloris flagellifera, Ch. nutans, Cynodon ambiguus, C. prostratus, Diplachne divaricatissima, Leptochloa anisopoda, L. exilis, Micrachne fulva, M. obtusiflora, M. patentiflora, M. pilosa, M. simonii, Stapfochloa berroi, S. canterae, S. ciliata, S. elata, S. parvispicula, Tetrapogon brandegeei, T. chlorideus, T. fasciculatus, T. pleistachyus, and T. roxburghiana; a new name, Cynodon simonii; and lectotypify Eleusine flagillifera.