Scientific name: Myriophyllum heterophyllum
What Is It?
Variable-leaf milfoil (Myriophyllum heterophyllum) is a rooted, perennial, aquatic plant that is native to the eastern United States. It has both underwater and above-water leaves and 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. This plant is on the Class A noxious weed list, and all five lakes are under strict management with an eradication goal.
Why Should I Care?
Variable-leaf milfoil is an aggressive noxious weed. Within a few years of introduction, it crowds out native plants and reduces habitat quality for fish, water birds, and other wildlife. The dense growth can prevent boating and be a hazard to swimmers. 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 2 distinct types of leaves. The above-water leaves are lance-shaped and 2 to 6 inches long.
- The underwater leaves are feathery and arranged around the stem in whorls of 4 to 6. Each leaf is divided into 5 to 14 pairs of leaflets.
- It usually grows in water up to 6 feet deep, but occasionally grows in deeper water.
- Flowers are in groups of 4 and are found from the spring through the fall. Toothed, leaflike structures (called bracts) are found below the flowers.
- It prefers neutral to slightly acidic water.
How Do I Distinguish It From 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.
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