Phylogeny of Vietnamosasa (Poaceae, Bambusoideae) based on syntenic nuclear genes with description of a new species

Vietnamosasa is a small paleotropical woody bamboo genus of the Bambusa - Dendrocalamus - Gigantochloa (BDG) complex with unresolved interspecific relationships. It grows in the dry dipterocarp forest and adapts to seasonal dryness and annual burning. Here, we reconstructed the phylogeny of Vietnamosasa using 938 syntenic nuclear genes. Our phylogenetic analysis based on four nuclear gene datasets from three subgenomes, i.e., subgenomes A, B, C, and all subgenomes combined, revealed that all species of Vietnamosasa , including a putative new species, clustered as a monophyletic group with high support, and Pseudobambusa is closely related to Vietnamosasa . Within Vietnamosasa , V. pusilla and V. darlacensis form a monophyletic group sister to V. ciliata . However, extensive discordance among gene trees indicates the complex reticulate evolution within Vietnamosasa . On the basis of morphological comparisons with the three published species of Vietnamosasa , together with phylogenomic evidence, we described a new species, V. sakonnakhonensis from Thailand, and provided a key to the four recognized species. The new species is distinguished from other species of Vietnamosasa by its wider foliage leaf blade and longer pistil.