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Morphological and Genetic Taxonomic Analysis of Native and Nonnative Watermilfoil in Reservoirs of the Lower Clark Fork River System

Madsen, J. D., Cheshier, J., Phuntumart, V. P., Thum, R. A., & Welch, M. E. (2010). Morphological and Genetic Taxonomic Analysis of Native and Nonnative Watermilfoil in Reservoirs of the Lower Clark Fork River System. Aquatic Plant Management Society 50th Annual Meeting. Bonita Springs, FL.

Abstract

Eurasian watermilfoil (Myriophyllum spicatum L.) was introduced to the Lower Clark Fork River system late in the decade of 2000, although it has been lower in the Pend Oreille River system for some time beforehand. The Lower Clark Fork River reservoirs (Thompson Falls, Noxon Rapids, Cabinet Gorge, and Pend Oreille Lakes, respectively, from upstream to downstream) have several native watermilfoil species, predominantly northern watermilfoil (Myriophyllum sibiricum). In 2008, we collected Eurasian watermilfoil and northern watermilfoil samples from six sites in each of the four reservoirs of the Lower Clark Fork River (only M. sibiricum was collected in Thompson Falls Reservoir, which did not have M. spicatum). We evaluated key morphological parameters on all specimens, including internode length, leaf length, leaflet length, number of leaflets per leaf, and stem thickness from six internodes per stem. Three independent laboratories performed three separate genetic analyses on all 42 specimens. Morphologically, reliable indicators between Eurasian watermilfoil versus northern watermilfoil were flattened (EWM) versus rounded (NM) apical meristem, flattened (EWM) versus rounded (NM) leaf tip, and more than 12 leaflet pairs (EWM) fewer than 12 leaflet pairs (NM). Genetic analysis from all three laboratories confirmed that morphological factors correctly identified the watermilfoil species. Also, genetic analysis did not indicate any evidence of hybridization of Eurasian watermilfoil with northern watermilfoil or any other native watermilfoil species.


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