Origins of polyploidy in Paspalum stellatum and related species (Poaceae, Panicoideae, Paspaleae) inferred from phylogenetic and cytogenetic analyses

摘要

Paspalum stellatum is widely distributed in the American continent and it is known to include diploid cytotypes (2n = 2x = 20) and polyploid cytotypes (2n = 32 and 52). It is closely related to P eucomum,P malmeanum and P. schesslii. After chromosome counting and geographical mapping of the different cytotypes, phylogenetic relationships between them were explored in order to infer the origin and evolution of the polyploid complex P stellatum and related species. Additionally, several unusual chromosome numbers are here reported for P. stellatum (2n = 30, 46, 48, 56 and 60) from the Brazilian cerrado. Phylogenetic analysis using plastid DNA showed that the cytotypes of P stellatum split into two clades, one of which included all accessions with 2n = 32 and P schesslii. Using ITS for phylogenetic analysis showed that P schesslii, P. malmeanum and P eucomum were grouped together as expected. The origin of the cytotype 2n = 32 of P. stellatum may have involved P. schesslii as one of the putative progenitors with a diploid cytotype of P. stellatum as the other.