Phylogenomics of Andropogoneae (Panicoideae: Poaceae) of Mainland Southeast Asia

Abstract—

The grass tribe Andropogoneae is distributed in warm regions around the globe but has been poorly studied in mainland Southeast Asia. This is particularly true for the cosmopolitan genera Andropogon and Schizachyrium, with several species that appear to be narrowly distributed in this region. Additionally, lesser-known species in the genera Hemisorghum, Kerriochloa, and Pseudosorghum also occur in mainland Southeast Asia. A phylogeny is needed to address questions of taxonomy and trait evolution. Whole chloroplast genomes of Andropogoneae species and two outgroup species of Garnotia (tribe Arundinelleae) were analyzed using maximum likelihood (ML) and Bayesian inference (BI). Ancestral character states were reconstructed using ML for four morphological characters key to Andropogon and Schizachyrium identification. A previously-unidentified clade of Southeast Asian endemic taxa is found, including one species formerly classified in Andropogon. Other Southeast Asian taxa fall in an unresolved grade outside the major radiation of the tribe. Andropogon and Schizachyrium are both polyphyletic. Convergent evolution and reversal of characters are common throughout Andropogoneae. Addition of species from mainland Southeast Asian finds unexpected phylogenetic diversity. Southeast Asian Schizachyrium sanguineum forms two separate clades, which could reflect cryptic species differentiation, hybridization, introgression, or some combination.