Phylogenetics of Paniceae (Poaceae)

Abstract

Paniceae demonstrate unique variability of photosynthetic physiology and anatomy, including both non-Kranz and Kranz species and all subtypes of the latter. This variability suggests hypotheses of independent origin or reversals (e.g., from C₄ to C₃). These hypotheses can be tested by phylogenetic analysis of independent molecular characters. The molecular phylogeny of 57 species of Paniceae was explored using sequences from the grass-specific insert found in the plastid locus rpoC2. Phylogenetic analyses confirmed some long-recognized alliances in Paniceae, some recent molecular phylogenetic results, and suggested new relationships. Broadly, Paniceae were found to be paraphyletic with Andropogoneae, Panicum was found to be polyphyletic, and Oplismenus hirtellus was resolved as the sister group to the remaining ingroup species. A particularly well-supported clade in the rpoC2 tree included four genera with non-Kranz species and three with distinctively keeled paleas. As previously suggested, the PCK (phosphoenol pyruvate carboxykinase) C₄ subtype arose once within Paniceae. All clades with non-Kranz species had Kranz ancestors or sister taxa suggesting repeated loss of the Kranz syndrome.