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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Publications at this Location » Publication #385722

Research Project: Integrated Weed Management and Restoration Strategies to Protect Water Resources and Aquatic and Wetland Ecosystems of the Far Western U.S.

Location: Invasive Species and Pollinator Health

Title: Identification of Watermilfoil, Discovery of Hybrid Watermilfoil, and Their Implications for Aquatic Plant Management in the Clark Fork River, Western MT, USA

item Madsen, John
item WERSAL, RYAN - Minnesota State University
item SCHMID, SAMUEL - Minnesota State University
item THUM, RYAN - Montana State University
item WELCH, MARK - Mississippi State University
item PHUNTUMART, VIPAPORN - Bowling Green State University

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2021
Publication Date: 5/6/2021
Citation: Madsen, J.D., Wersal, R.M., Schmid, S.A., Thum, R.A., Welch, M., Phuntumart, V. 2021. Identification of Watermilfoil, Discovery of Hybrid Watermilfoil, and Their Implications for Aquatic Plant Management in the Clark Fork River, Western MT, USA. Biological Invasions. 36(1):111-124.

Interpretive Summary: This research statistically substantiates that pure strain Eurasian watermilfoil and pure strain northern watermilfoil can be consistently and reliably differentiated based on one of three characteristics: leaflet number, rounded versus flattened apical meristem, and rounded versus flattened leaf tip. Otherwise, there are no simple characteristics to differentiate the invasive from the native species. These characteristics, however, are not reliable once hybridization occurs. At the time of this study, hybridization had not occurred.

Technical Abstract: Eurasian watermilfoil (Myriophyllum spicatum) is an invasive submersed macrophyte that has infested many waters in North America since its introduction. Eurasian watermilfoil has the ability to alter the structure and function of the ecosystems that it invades. Eurasian watermilfoil was first surveyed in the Clark Fork River, MT in 2008, alongside the native northern watermilfoil (Myriophyllum sibiricum). Three reservoirs (Cabinet Gorge, Noxon Rapids, and Thompson Falls) on the lower Clark Fork River had entire lake surveys conducted using the point intercept method. Morphological data from these surveys showed that only Eurasian watermilfoil and northern watermilfoil were present during the time of the surveys in 2008. The results of the morphological identification were supported by molecular identification at three different laboratories. In 2016, a genetic survey of watermilfoil species was conducted on the Noxon Rapids Reservoir and found that hybrid watermilfoil (Myriophyllum spicatum x sibiricum) was present. This hybridization event poses a number of issues for aquatic plant management. Hybrid watermilfoil is much more difficult to identify morphologically than its parent types. The hybrid is also more invasive and may be differentially susceptible to some herbicides than the parental type Eurasian watermilfoil.