Variable-Leaf Milfoil, and Hybrid variable-leaf milfoil
Myriophyllum heterophyllum, Myriophyllum heterophyllum x Myriophyllum hippuroides
Washington State Classification
Class A — Eradication Required Statewide
It’s an invasive plant that can alter aquatic ecosystems.
Quick Reference
Identification
Growth Habit
It is a submersed, rooted aquatic plant, having both submerged and emergent leaves growing from a stout stem up to .18 inches in diameter and 3.25 feet in length.
Leaves
Emergent spikes are 2 to 6 inches long with persistent, lance shaped to oblong leaves. It has prominently serrated bracts that are reflexed, extend past the flowers. Submerged leaves are whorled and dissected, feather-like, with 7 to 11 leaflets.
Flowers
The infloresence is a spike 1.9 to 13.8 inches long consisting of flowers in whorls of four. Flowers have four stamens, and petals are 0.06 to 0.12 inches.
Impact
It’s an invasive plant that can alter aquatic ecosystems. It forms mats that shade out native plants and inhibits water flow and recreational activities. It may be able to hybridize with the native watermilfoil resulting in a more aggressive hybrid.
Ecology & Spread
Habitat
It grows in freshwater ponds, lakes, ditches and other still or flowing aquatic systems. Please click here to see a county level distribution map of variable-leaf milfoil in Washington.
Spread Mechanisms
Reproduction
It primarily reproduces vegetatively by plant fragments but can also reproduce by seeds. It can easily be introduced into new bodies of water through inadvertent transport of plant fragments on boats and boat trailers or deliberate dumping of aquariums.
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Control Methods
Mechanical
- Small infestations may be hand removed or tarped. The entire plant must be removed.
Cultural / Prevention
- Reduce weed infestation by handpulling weeds. Digging and carefully removing all rhizomes will effectively eliminate single plants and small infestations.