Haplotypes of Fallopia introduced into the US

In the US, clonal growth of Fallopia japonica, Fallopia sachalinensis and their hybrid Fallopia x bohemica (Polygonaceae) is prominent, yet sexual reproduction and hybridization contribute to the genetic complexity of swarms. The contribution to this diversity from multiple introductions is unknown. Using 800 bp of the non-coding chloroplast marker accD-rbcL, we compared 21 Japanese haplotypes with 46 US samples from 11 states, 2 Canadian samples, and 6 European samples from 4 countries, in order to investigate if there were repeated introductions from Asia. While most North American and all European haplotypes accessions in our collection matched a single widespread haplotype, we identified 8 other haplotypes. Three haplotypes of F. japonica (including the widespread haplotype) and one F. sachalinensis matched previously identified Japanese haplotypes, supporting the hypothesis of multiple introductions in the US. Five additional US haplotypes were detected once. Four of these differed from Japanese haplotypes by one single nucleotide polymorphism (SNP), possibly indicating a recent in situ change. The fifth haplotype represents a garden cultivar, which differed from all F. japonica haplotypes. It therefore appears that the US genetic diversity of these taxa has three sources: intra-specific reproduction, inter-specific reproduction, and multiple sources of introduction.