Introgressive Hybridization in Mesomorphic Bluegrasses, Poa Section Stenopoa, in Western Siberia

The mesomorphic Poa palustris and P. nemoralis (section Stenopoa) have generated a taxonomically complicated hybrid aggregate, which is known as P. intricata. In order to study the morphological and genetic diversity of P. intricata in western Siberia, we analyzed six populations from a range of geographical locations and ecological conditions in the study area, and one “typical” population of P. nemoralis from a European locality. Results of morphometric multivariate analyses based on 29 characters and 699 individuals revealed that most of the populations contain a mixture of morphotypes, combining character states of both parental species. These transitional forms showed neither geographical nor ecological affiliation. No genetic structure was found using ISSR markers, suggesting continuous gene flow. Our results suggest a hybrid origin of almost all the studied P. nemoralis and P. palustris individuals in western Siberia, which taxonomically can be attributed to P. intricata aggr.