Phylogenetics of the Bouteloua curtipendula complex (Gramineae: Chloridoideae)

The Bouteloua curtipendula complex (Gramineae: Chloridoideae) (BCC) is a group of 11 species native to the American grasslands. It is distributed from Canada to Argentina with its center of diversity in Mexico. Many branches per inflorescence, few spikelets per branch, and branches deciduous at maturity characterize the BCC. Due to considerable morphological variation, putative hybridization, polyploidy (including aneuploidy) and apomixis, circumscription and relationships among taxa has been uncertain. All previous studies of the BCC were based on morphological and cytological characters, and no explicit phylogenetic hypothesis had been proposed. In order to infer the phylogenetic relationships, two non-coding regions, the internal transcribed spacer region of the nuclear ribosomal DNA (ITS) and the trnT-L-F region from the chloroplast DNA were sequenced and subjected to a cladistic parsimony analysis. Character state reconstruction analysis was carried out to examine the principal morphological characters used to circumscribe species. Three samples found to be in different positions in the phylogenies were cloned to ascertain the existence of different ITS copies. Likewise, 66 chromosome counts were obtained from samples DNA sequenced and mapped onto the ITS strict consensus tree. Results demonstrated the monophyly of the complex but not the monophyly of its constituent taxa, except for the morphological distinct B. triaena, which formed a strongly supported clade in both phylogenies. The phylogenies displayed some congruence with morphology and chromosome numbers. The principal morphological taxonomic characters were all found to be homoplasious. Bouteloua curtipendula and B. purpurea were the only polyploid taxa ranging from 2n = 21 to >100. Different paralogous of ITS along with chromosome number show that allopolyploidy has occurred on the BCC. Polyploidy was found to be apomorphic.