Scientific name: Myriophyllum heterophyllum

What Is It?

Variable-leaf milfoil is a submersed, rooted, perennial, aquatic plant that is native to the eastern United States. It has both underwater and emergent leaves with dark red to reddish brown stems. It is found in freshwater lakes, ponds, and slow moving rivers.

Is It Here Yet?

Yes, variable-leaf milfoil is in five lakes in Pierce and Thurston Counties in western Washington. This plant is included on the Class A noxious weed list, and all five lakes are under management with eradication as the goal.

Why Should I Care?

Variable-leaf milfoil is an aggressive invader in Washington. Within a few years of introduction, it crowds out native plants and reduces habitat quality for fish, waterfowl, and other wildlife. The dense growth also can be a hazard to swimmers and a nuisance to boaters. In addition, controlling established populations is both difficult and expensive.

How Can We Stop It?

  • Do not purchase, plant, or trade this species.
  • Variable-leaf milfoil was sold as an aquarium plant. It is now illegal to buy or sell it in Washington.
  • Take care not to purchase aquarium plants from other states.
  • Never allow aquarium or water garden plants to escape to natural water bodies.
  • Be sure to clean, drain, and dry boats and other gear thoroughly between visits to different lakes and rivers.

What Are Its Characteristics?

  • Variable-leaf milfoil has two distinct types of leaves. The submerged plant has featherlike leaves, arranged in whorls of four to six around the stem.
  • Each leaf has 5 to 14 pairs of leaflets.
  • It usually grows in water up to 6 feet deep, but occasionally grows in deeper water.
  • Variable-leaf milfoil flowers from the spring through the fall.
  • It prefers neutral to slightly acidic water.

How Do I Distinguish It Form Native Species?

The variable-leaf milfoil may be confused with the native western milfoil, M. hippuroides. If you need help with plant identification, please contact your local county weed board.

Additional Photographs