Pathways of introduction of the invasive aquatic plant C abomba caroliniana

The pathway and frequency of species' introductions can affect the extent, impact, and management of biological invasions. Here, we examine the pathway of introduction of the aquatic plant C abomba caroliniana (fanwort) into Canada and the northern U nited S tates using plastid DNA sequence (intergenic spacers atpF ‐ atpH , trnH ‐ psbA, and trnL ‐ trnF ) and DNA content analyses. We test the hypothesis that the spread of fanwort is a result of commercial trade by comparing a C anadian population ( K asshabog L ake, ON ) to native populations from southern U.S., introduced populations in northern U.S., and plants from commercial retailers. Thirteen plastid haplotypes were identified throughout North A merica, including one dominant haplotype, which was present in all C . caroliniana populations. Several rare haplotypes were used to infer shared colonization history. In particular, the C anadian population shared two rare alleles with a population from M assachusetts, suggesting range expansion of C . caroliniana from the northern U.S. However, the possibility of a commercial introduction cannot be excluded, as common alleles were shared between the C anadian population and both commercial and southern U.S. sources. Variation in C . caroliniana genome size was bimodal and populations were classified into “high” and “low” categories. The C anadian population had DNA contents similar to several northern U.S. populations (low DNA content). This may provide additional support for range expansion from these introduced populations rather than from commercial sources or populations in the southern U.S., which had high DNA content.