A DNA fingerprinting approach for distinguishing native and non-native milfoils

Variable-leaf water milfoil, Myriophyllum heterophyllum, is a non-native aquatic plant that has become a major management concern in New England. One key obstacle for effective management is accurate identification of native and non-native milfoil species. We used DNA sequences from the nuclear ribosomal DNA internal transcribed spacers (ITS) to identify non-native populations of M. heterophyllum. We found a number of discrepancies among morphological and genetic identifications, including individuals that were morphologically identified as natives but genetically identified as non-natives, and vice versa. We attribute these discrepancies to inaccurate identifications arising from morphological similarities among milfoil species. To help remedy this problem, we developed a restriction enzyme assay that distinguishes non-native M. heterophyllum from native milfoils. The assay provides a reliable method for identifying M. heterophyllum and therefore should facilitate lake management decisions concerning native and non-native milfoil populations.