The phylogenetics of Poaceae is generally well-studied with the exception of the large and variable Paniceae within which intergeneric relationships are uncertain. 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 both hypotheses of independent origin and reversals (e.g. from kranz to non-kranz). These hypotheses can be tested by phylogenetic analysis of independent molecular characters. The molecular phylogeny of 60 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 as well. 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 PEP-ck subtype arose once within Paniceae. All clades with non-kranz species had kranz ancestors or sister taxa suggesting repeated loss of the kranz syndrome. Other correlations between photosynthetic physiology and molecular phylogeny await further study.

Key words: kranz, molecular phylogenetics, non-kranz, Paniceae, Poaceae rpoC2 insert