Phylogeny of Andropogoneae inferred from phytochrome B, GBSSI, and NDHF

Andropogoneae is a monophyletic tribe of 85 genera that includes Zea and Sorghum. All members exhibit C-4 photosynthesis and have inflorescences of paired spikelets. Previous studies of the chloroplast gene ndhF and the nuclear gene GBSSI identified numerous mutations that distinguish genera of the tribe but do not indicate relationships among them; the deep branches of the trees are quite short. Here we add newly collected data from phytochrome B to the data from the other two genes. The same pattern holds, with very short branches along the backbone of the tree indicating that the tribe resulted from rapid radiation. The phylogeny shows a single origin of a disarticulating rachis, which is a synapomorphy for the tribe. We find strong support for a core Andropogoneae that includes Andropogon, Bothriochloa, Capillipedium, Cymbopogon, Dichanthium, Heteropogon, Hyparrhenia, and Schizachyrium and support for its relationship with an expanded Saccharinae that includes Microstegium. The combined data reject the monophyly of subtribes Andropogoninae and Anthistiriinae and provide evidence that subtribes Sorghinae, Saccharinae, and Rottboelliinae are paraor polyphyletic, as is the traditional Maydeae. A relationship with Zea and Tripsacum is indicated for Elionurus, while Chionachne and Phacelurus are shown to diverge early in the history of the tribe. Arundinella hirta and Arundinella nepalensis can be included in an expanded Andropogoneae.