Reassessing the phylogenetic relationships of Pseudosorghum and Saccharinae (Poaceae) using plastome and nuclear ribosomal sequences

The sugarcane subtribe Saccharinae (Andropogoneae, Poaceae) was established in 1846, but its delimitation has long been debated. Moreover, the relationships among the genera of Saccharinae remain unclear, and there is no consensus on whether <i>Pseudosorghum</i>, a small genus in tropical Asia with only two species, should be included. Here, we performed phylogenomic analyses using whole plastomes (69 of them newly sequenced) from 132 individuals, representing 65 species in 19 related genera. We also built trees with nuclear ribosomal DNA sequences. Our results justify the inclusion of <i>Pseudosorghum</i>, likely also the <i>Eulalia</i> Clade III, in Saccharinae. Furthermore, both morphological and molecular analyses support merging the two <i>Pseudosorghum</i> species. The backbone relationships of the Saccharinae phylogeny were highly supported with four polyphyletic clades of <i>Miscanthus</i> and the inclusion of <i>Narenga</i> and <i>Tripidium rufipilum</i> in <i>Saccharum</i>. <i>Pseudosorghum</i> is moderately supported as sister to the <i>Miscanthus</i> Clade I, while the remaining <i>Tripidium</i> species could be excluded from the subtribe. Saccharinae is estimated to have originated ∼3.73 million years ago in East Asia, followed by intercontinental dispersals. Our study provides a comprehensive phylogenetic framework for future taxonomic revisions of this economically important subtribe.