Date Approved


Graduate Degree Type


Degree Name

Biology (M.S.)

Degree Program


First Advisor

James McNair

Second Advisor

Ryan Thum

Third Advisor

Timothy Evans

Fourth Advisor

Sheila Blackman


Invasive plants are a major concern for environmental managers. Cryptic invasive taxa present additional challenges because of their potential to respond differently to management efforts. Invasive Eurasian watermilfoil (Myriophyllum spicatum) and hybrid watermilfoil (Myriophyllum spicatum x Myriophyllum sibiricum) cannot be reliably distinguished based on morphological characters and are therefore cryptic taxa. Laboratory studies show that on average, hybrid watermilfoil grows faster, branches more, and is less responsive to standard control measures developed for Eurasian watermilfoil. These laboratory results predict less effective control of hybrid watermilfoil in mixed populations treated uniformly with one of these control measures. However, to date there have been no explicit comparisons of growth and response of hybrid versus Eurasian watermilfoil under operational management. In this study, I use genetic methods to distinguish morphologically cryptic Eurasian and hybrid watermilfoil, and document for the first time that the two taxa exhibit divergent responses to treatment with 2,4-dichlorophenoxyacetic acid- amine and triclopyr under operation management in Houghton Lake, Michigan. Results show that treatment was much more effective for pure Eurasian watermilfoil than for hybrids. These findings provide a concrete example of how cryptic invasive taxa can impact control efficacy and how incorporating genetic methods into monitoring can improve treatment assessment and vegetation monitoring, potentially improving management.

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