Comparative Plastomes and Phylogenetic Analysis of and Closely Related Genera (Poaceae).

(Orininae, Cynodonteae, Chloridoideae, Poaceae) is an ecologically important genus. The phylogenetic placement of and phylogenetic relationships among taxa remain controversial for a long time. To resolve the intra- and inter-generic relationships of , the plastomes of 12 taxa (including 8 species and 4 varieties), one species, 15 species, two species, and two species were included in the present study. All the taxa showed a similar pattern in plastome structure, gene order, gene content, and IR boundaries. The number of simple sequence repeats ranged from 145 () to 161 ( and ). Moreover, 1,687 repeats were identified in these taxa, including 1,012 forward, 650 palindromic, 24 reverse, and one complement. Codon usage analysis revealed that these plastomes contained 16,633 () to 16,678 () codons. Sequence divergence analysis among and closely related genera identified five non-coding regions (, , , , ). Phylogenetic analysis of complete plastomes indicated that is sister to a clade composed of and , whereas it did not support the sister relationship between the recently proposed subtribe Orininae ( and ) and . The subtribe Orininae was not supported by our complete plastome data. The split between and - clade go back to 14.01 Ma. Besides, our findings suggested that and are the successive early diverging groups in the phylogenetic analysis. The other 10 taxa are divided into two groups: a monophyletic group composed of sp. nov. and var. is sister to other eight taxa. was estimated to have experienced rapid divergence within a short period, which could be a major obstacle in resolving phylogenetic relationships within . Collectively, our results provided valuable insights into the phylogenetic study of grass species.