Phylogenetic relationships of Piptochaetium Presl (Poaceae: Stipeae) and related genera reconstructed from nuclear and chloroplast sequence datasets

Piptochaetium (Poaceae, Pooideae, Stipeae) is a New World genus of grasses distributed primarily in temperate South America, with several species extending into Central and Southern North America. The genus comprises 36 species and 2 varieties. Morphological synapomorphies for the genus include involute lemma margins that fit into the palea groove, a bi-keeled palea longer than the lemma and protruding from the lemma apex, and fundamental cell sidewalls that are regularly dentate. The closely related genera Nassella (116 species) and Jarava (59 species) are also primarily South American, with a few species found in Central and North America. Published molecular studies to date have focused upon generic-level relationships within the tribe Stipeae, but none have included more than a few representatives of each genus. We present here results of phylogenetic analyses of these genera based upon combined DNA sequences of both nuclear (ITS) and cpDNA (rplI6, trnL-F) markers. Piptochaetium is Supported as monophyletic in all studies, whereas Nassella is recovered as monophyletic only if Jarava plumosa is included. Infrageneric relationships of Piptochaetium are also compared to a recent morphological phylogeny of the genus.