A phylogenetic study of subtribe Otachyriinae (Poaceae, Panicoideae, Paspaleae)

The subtribe Otachyriinae was established, within tribe Paniceae, by Butzin in 1970, originally including 18 genera. Recent phylogenetic studies, based on molecular data, indicated that Otachyriinae belongs to tribe Paspaleae and is represented by the genera Anthaenantia, Hymenachne, Dallwatsonia, Otachyrium, species of Panicum sect. Laxa, Plagiantha, and Steinchisma. These taxa show a peculiar diversity in photosynthetic types, including C-4 species, C-3-C-4 intermediates and C-3 species. The internal evolutionary relationships among members of Otachyriinae have not yet been explored in detail. With the aim of providing new evidence to understand phylogenetic relationships of taxa included in Otachyriinae, 21 new sequences of the ndhF gene from 34 species were generated and analyzed using Bayesian inference and maximum parsimony (MP). The evolution of photosynthetic pathway was studied employing MP, Markov chain Monte Carlo, and maximum likelihood methods. Our results confirm that subtribe Otachyriinae is monophyletic. Within the subtribe, Anthaenanthia is a monophyletic C-4 genus and is sister to the remaining species included in this treatment. Hymenachne and Panicum sect. Laxa, in its traditional concept, are polyphyletic; Dallwatsonia, P. auritum, and P. hemitomon are treated within Hymenachne, while three species of Panicum sect. Laxa are considered a new genus in the subtribe. The genus Otachyrium is paraphyletic, while all species of Steinchisma are recovered as a monophyletic group with high support. Finally, our data suggest that C-4 and C-3-C-4 photosynthesis evolved just once each during the speciation of the subtribe from a C-3 ancestor.