Molecular Characterization of Eurasian Watermilfoil, Northern Milfoil, and the Invasive Interspecific Hybrid in Michigan Lakes

The presence of invasive aquatic plants can be detrimen- tal to the ecology of lakes and reservoirs. The distribution of the introduced plant pest Eurasian watermilfoil ( M. spica- tum ), the native Northern milfoil ( M. sibiricum ), and the inva- sive interspecies hybrid ( M. spicatum · M. sibiricum ) was surveyed in 14 Michigan lakes and one lake in northern Indi- ana. Although M. spicatum , M. sibiricum , and the hybrid are morphologically similar, they can clearly be distinguished from each other by sequencing the nuclear rRNA internal transcribed spacer region (rRNA ITS). We described 11 mu- tations that can be used to unambiguously identify M. spica- tum , M. sibiricum , and the hybrid at the DNA level. We identified additional mutations that can be used to differen- tiate between variants within a species. Both invasive species, M. spicatum and the hybrid, are widespread in Michigan lakes. M. sibiricum was rarely found in the lakes studied. M. spicatum and the hybrid were found to coexist in the majority of the lakes studied, in direct contrast to previous studies.