Polyploids and geographic divergence blur species delimitation in the Paspalum stellatum complex (Poaceae: Paspaleae)

Abstract

Paspalum stellatum comprises a diploid and several polyploid cytotypes. The widely distributed cytotype 2n = 32 is an amphidiploid, an outcome of hybridization between diploid P. stellatum (2n = 20) and the related species Paspalum schesslii (2n = 12). Several analyses were conducted upon a set of 24 accessions of P. stellatum and representatives of three related species. Multivariate analyses of morphological data discriminated between the two potentially sexual cytotypes, 2n = 20 and 2n = 32, but the putatively apomictic higher polyploids were interspersed between them. Instead, Iner Simple Sequence Repeat (ISSR) markers separate two main groups geographically, west and east from the Brazilian-Bolivian Pantanal. Both groups include diploid (2n = 20) and tetraploid (2n = 32) cytotypes, but higher polyploids belong exclusively to the eastern group. Considering that diploids and polyploids behave as different biological entities, we propose to treat the diploid (2n = 20) cytotype as a different species, for which the name Paspalum cujabense should be rehabilitated. Meanwhile, the name P. stellatum remains for a complex including the tetraploid and all polyploid cytotypes.