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Washington State Weeds

Variable-Leaf Milfoil

variable-leaf milfoil

 Myriophyllum heterophyllum  • Class A

Family Name: Haloragaceae family  (HAL-uh-ruh-gay-see-ee)
Common: Watermilfoil family
Genus: Myriophyllum (my-ree-oh-FIL-um)
Meaning: Numberless leaves
Species: heterophyllum (het-er-oh-FY-lum)
Meaning: Differently leaved

Variable leaf milfoil is a submersed, rooted aquatic plant, that has both submerged and emergent leaves growing from a stout reddish brown stem.

Submerged leaves are from 1 to 2 inches long and arranged in whorls of 4 -5 finely divided (feather-like) leaves.

Emergent spikes are 2 to 6 inches long with lance-shaped to oblong leaves.

From spring through fall, tiny white flowers occur in the axils of the bracts on emergent flower spikes. Flowers and bracts are arranged in whorls.

It is rooted in the bottom of water bodies and grows up. When it reaches the surface of the water, the stems turn and grow horizontally.  

 Why Is it a Noxious Weed?

This invasive aquatic plant can alter aquatic ecosystems. It forms dense mats that shade out other native aquatic plants, inhibits water flow, and recreational activities. It may be able to hybridize with the native watermilfoil, resulting in an even more aggressive hybrid. 

Where Does it Grow?

Found in freshwater ponds, lakes, ditches and other still or flowing aquatic systems. It thrives in older more stabilized systems with clear, acidic water, where it may be rooted in depths up to 10 feet. 


Variable-Leaf Milfoil spreads primarily through vegetative fragments, although it may also reproduce via seed production. 

It may be introduced into new bodies of water through the unintentional transport of plant fragments attached to boats and boat trailers, or the deliberate dumping of aquariums. 

Control Options:
  • As with all invasive species, the best form of control is prevention. Carefully inspect and clean boats, trailers, and fishing gear to prevent transporting plant materials from one body of water to another. Never discard aquarium plants in sewer systems or water bodies. 
  • Small infestations can be hand pulled, making sure to remove the entire plant. Some success has been achieved with draw down techniques, though other species are impacted as well. 

  • Since Variable-Leaf Milfoil is an aquatic plant, the use of an herbicide formulated for aquatic settings is required
  • Please note that aquatic herbicides are restricted for use in Washington State to licensed applicators only. 

More Information:

 Download our Flyer or visit Washington State Noxious Weed Control Board Here. Photo by Leo Michels


More Pictures:  

variable-leaf milfoilvariable-leaf milfoilvariable-leaf milfoil