Assessing the genetic diversity of Nymphoides peltata in the native and adventive range using microsatellite markers

Nymphoides peltata (yellow floating heart), native to Eurasia, is an invasive plant in the USA, where it grows in relatively isolated but widespread populations. The species is capable of sexual reproduction by seed and asexual reproduction through fragmentation. Although N. peltata is recognized as a noxious weed, little is known about its geographic region of origin or its dispersal mechanisms and relative amount of genetic variation in its adventive range. We conducted a genetic analysis of N. peltata by studying 68 localities across the native range and 47 localities in the adventive range, using microsatellite markers to determine genetic variability within and among populations, and to infer regions in the native range from which invasive plants originated. A large number of sites in the USA were genetically identical to one another, and there were two predominant multilocus allele phenotypes that were distributed in the northern and southern latitudes, respectively. Additional USA sites were similar to one of the predominant genetic profiles, with greater genetic diversity in southern populations. The genetically identical sites are consistent with asexual spread, potentially via anthropogenic mechanisms. Plants across the USA range were observed to produce viable seeds, and some genetic variation could be explained by sexual reproduction. All USA plants were more similar to plants in Europe than they were to plants in Asia, indicating that the plants likely were introduced originally from Europe. The existence of two genetic clusters and their similarity to plants in different parts of Europe constitute evidence for at least two N. peltata introductions into the USA.