Diversity and origins of Butomus umbellatus (flowering rush) invasion in North America.
Flowering rush (Butomus umbellatus) is an invasive aquatic plant in northern USA and southern Canada. To better understand the pattern of invasion in North America and implications for management, we investigated genetic diversity and population structure of the more recent western North American invasion and compared it to the earlier eastern North America invasion using 80 variable AFLP loci. We found six invasive genotypes, indicating multiple founding events, with primarily monotypic populations indicating clonal reproduction. The genetic makeup and ploidy of the western North America populations is distinct from the earlier eastern North American invasion, with different genotypes and ploidy levels dominating different regions. Flowering rush is under consideration for classical biological control, and initial studies show that some genotypes are resistant or tolerant to a proposed plant pathogen. To inform biological control development and direct foreign exploration, we compared genetic data with Eurasian native samples and found an exact genetic match for the common western North American genotype in the Netherlands, and propose best estimates of origins for the other invasive genotypes. The different genetic makeup of the invasion at regional scales, and their differing phenotypes in terms of reproductive mode and susceptibility to highly host-specific biological control supports the investigation of specialized management programs for different portions of the North American invasion.