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Extreme differences in population structure and genetic diversity for three invasive congeners: knotweeds in western North America

John F. Gaskin, Mark Schwarzländer, Fritzi S. Grevstad, Marijka A. Haverhals, Robert S. Bourchier, Timothy W. Miller
Biological invasions 2014 v.16 no.10 pp. 2127-2136
Reynoutria japonica, invasive species, hybrids, amplified fragment length polymorphism, asexual reproduction, genotype, genetic variation, ecological invasion, Reynoutria sachalinensis, population structure, biogeography, British Columbia, South Dakota, California
Japanese, giant, and the hybrid Bohemian knotweeds (Fallopia japonica, F. sachalinensis and F. x bohemica) have invaded the western USA and Canada, as well as other regions of the world. The distribution of these species in western North America, and their mode of invasion, is relatively unresolved. Using Amplified Fragment Length Polymorphisms of 865 plants from 132 populations from British Columbia to California to South Dakota, we determined that Bohemian knotweed was the most common species (72% of all plants). This result is in contrast to earlier reports of F. x bohemica being uncommon or non-existent in the USA, and also differs from the European invasion where it is rare. Japanese knotweed was nearly monotypic, while giant knotweed and Bohemian knotweed were genetically diverse. Genotypic data suggests that Japanese knotweed in western North America spreads almost exclusively by vegetative reproduction, whereas Bohemian knotweed spreads by both seed and vegetatively, over both long and short distances. Giant knotweed populations were mostly monotypic, with most containing distinct genotypes, suggesting local spread by vegetative reproduction. Spread of giant knotweed over long-distances appears to be by seed or alternatively there have been multiple introductions of different genotypes to separate locations. The high relative abundance and genetic diversity of Bohemian knotweed make it a priority for control in North America.