Extensive reticulate evolution within Fargesia (s.l.) (Bambusoideae: Poaceae) and its allies: Evidence from multiple nuclear markers.

Reticulate evolution resulting from hybridization and introgression has been recognized as a creative source of species and diversification in bamboos. Previous phylogenetic studies revealed that Fargesia (s.l.) (Fargesia and Yushania) was divided into the Fargesia spathe clade and the non-spathe clade. Interestingly, the Fargesia spathe clade may have originated from hybridization among other clades within Fargesia (s.l.). Understanding the hybrid origin of this clade requires a robust phylogenetic framework in which major clades within Fargesia (s.l.) are resolved. Here, we used three nuclear genes to reconstruct the evolutionary history of Fargesia (s.l.) and its allies to identify putative patterns in the origin of the Fargesia spathe clade and to examine the extent to which reticulate evolution has occurred at the interspecific level in bamboos. Bashania species form a clade with Fargesia (s.l.), which is further divided into Group I and Group II. The Fargesia spathe clade, the Alpine Bashania clade, and Fargesia yajiangensis comprise Group I, while the Bashania fargesii clade and the remaining Fargesia (s.l.) species form Group II. Incongruence between the current nuclear-based and previous plastid phylogenies demonstrate several possible hybridization events among Fargesia (s.l.) species and related taxa, which have given rise to the Fargesia spathe clade, the Phyllostachys clade, and the Ampelocalamus clade. We also detected several putative hybrid species of Fargesia (s.l.). Our results show that reticulate evolution has played a prominent role in Fargesia (s.l.) evolution, which could, in part, account for the taxonomic difficulty associated with Fargesia (s.l.) and the alpine bamboos. The study also underscores the importance of hybridization in the evolution of bamboos, at both intergeneric and intrageneric levels.

Straight From the Plastome: Molecular Phylogeny and Morphological Evolution of Fargesia (Bambusoideae: Poaceae).

Fargesia is ecologically and economically important in mountainous forests. Many Fargesia species are also important sources of food for some endangered animals such as the giant panda. Recent molecular phylogenetic analyses have revealed Fargesia as a polyphyletic group despite some unclear lineage affinities. In the present study, we reconstructed the phylogeny of Fargesia and its allies, including Thamnocalamus, Arundinaria (incl. Bashania), Yushania, Indocalamus, Ampelocalamus and Phyllostachys, from a plastome sequence matrix that contained 20 Fargesia and five Yushania species as ingroups, 16 species from nine other bamboo genera plus Oryza sativa and Zea mays as outgroups. Fargesia and its allies were broken into eight clades. Several Fargesia species were clustered into the Thamnocalamus clade and the Drepanostachyum + Himalayacalamus clade that rendered the polyphyly of Fargesia. The remaining six clades, including the Fargesia spathe clade, the Phyllostachys clade, Arundinaria fargesii, the Ampelocalamus clade, the Fargesia grossa clade, and the Fargesia macclureana clade, were identified. Molecular phylogenetic analyses supported that Yushania should be included in Fargesia (s.l.) which had synapomorphy of expanded leaf sheaths in varying degree at the basis of inflorescences, and further divided into the Fargesia spathe clade, the Fargesia grossa clade, and the Fargesia macclureana clade. All sampled species of Yushania were nested within the Fargesia grossa clade. The probable model of the origin of the species in the Fargesia spathe clade with spathe-like leaf sheath syndrome was proposed. Moreover, the formation of the spathe-like leaf sheath syndrome may be correlated with cold climatic conditions in Quaternary. Our results provide new sight into the phylogenetic relationship within Fargesia.