Taxon delimitation, chromosome numbers and genetic diversity of Paspalum polyphyllum and P. bicilium (Poaceae, Paspaleae)

The South American Paspalum polyphyllum and P. bicilium need accurate species delimitation. The aim of this study was to assess morphological variation, through morphometric analysis of specimens from natural populations, chromosome number and genetic diversity of populations based on inter-simple sequence repeat (ISSR) molecular markers, to test taxonomic relationships among these species and other related species. We analyzed 183 individuals of P. polyphyllum and P. bicilium from 31 natural populations from Brazil, Argentina and Bolivia. Multivariate analyses from 23 morphological characters allowed the distinction of P. bicilium from P. polyphyllum, and the most important characters were: rachis width, spikelet and upper floret length. For both species, most of the genetic diversity was shown among the populations (88.36% of the total mean variation in P. polyphyllum and 84.31% in P. bicilium), while the diversity within the populations was low (11, 64% and 15.69%, respectively). Cytogenetic studies revealed a new chromosome number (2n = 36) for P. polyphyllum and P. bicilium, and 2n = 46 for P. burmanii. Results obtained made it possible to recognize P. bicilium as a distinct species from P. polyphyllum. We provide a taxonomic treatment including species descriptions, a distribution map, illustrations, and a comparative table for P. bicilium and P. polyphyllum, besides preliminary data for five related species of Paspalum subgen. Ceresia.