Hybridization between native and invasive Nymphoides species in the United States

The presence of hybrid genotypes resulting from the mating of native and invasive species poses numerous problems to invasive species managers, including initial difficulty in hybrid detection, unpredictable ecological impacts to recipient ecosystems, and variability in response to management actions. We conducted a molecular study of internal transcribed spacer sequences to determine whether hybridization has occurred between the North American macrophyte Nymphoides aquatica and the invasive N. cristata where their distributions overlap in the southeastern United States (US). A hybrid N. aquatica × N. cristata population was detected within Lake Moultrie, in South Carolina. Given the broad geographic overlap in the distributions of N. aquatica and N. cristata in the southeastern US, and previously documented hybridization between the natives N. aquatica and N. cordata , additional monitoring for hybrid populations throughout the introduced range is strongly suggested. At a minimum, hybrid monitoring should take place in the nine counties of three states where both species are documented. Here, we discuss next steps to better characterize genetic diversity within hybrid Nymphoides populations and the potential management implications.