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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: variable-leaf watermilfoil

Synonyms and Other Names: None

Taxonomy: available through www.itis.gov

Identification: A perennial herbaceous submersed aquatic plant that produces a short, emergent floral spike above the waterline.  Submersed leaves (2-4.5 cm long) are pinnately divided into 4-10 leaflet pairs, giving them a feather-like appearance and are arranged in whorls of 4-6 around a stout stem (3 mm in diameter).  

Native Range: Native to United States, but historically known only in the Southeast and Midwest.  

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Means of Introduction: Released aquarium or pond plants. Secondary spread possible through hitchhiking on boats/trailers or waterfowl.

Remarks: Molecular data supports the fact that some aggressively growing populations of variable-leaf milfoil are actually hybrids between M. heterophyllum and the native M. pinnatum; these hybrids, found in Connecticut, propagate primarily vegetatively (Moody & Les 2002).  Populations sampled from 25 lakes in New Hampshire, however, suggest that the pure M. heterophyllum is also capable of forming aggressively-spreading, monotypic stands (Thum & Lennon 2006).

References: (click for full references)

Crow, G. E. and C. B. Hellquist.  2000. Aquatic and wetland plants of Northeastern North America.  Volume 1. The University of Wisconsin Press, Madison, Wisconsin.

Les, D.H. and L.J. Mehrhoff. 1999. Introduction of nonindigenous aquatic vascular plants in sourhtern New England: a historical perspective. Biological Invasions. 1(2/3). pp. 281-300.

Moody, M.L. and D.H. Les. 2002.  Evidence of hybridity in invasive watermilfoil (Myriophyllum) populations.  Proceedings of the National Academy of Science 99(23): 14867–14871.

Thum, R.A. and J.T. Lennon. 2006. Is Hybridization Responsible for Invasive Growth of Non-indigenous Water-milfoils?  Biological Invasions 8(5): 1061-1066. 

Other Resources:

Author: Howard, V.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.