Scientific name: Myriophyllum spicatum
What Is It?
Eurasian watermilfoil (Myriophyllum spicatum) is a submersed plant that grows in a variety of still and flowing freshwater bodies. It can tolerate a range of salinity, acidity, and temperature. Watermilfoil forms dense mats that shade native aquatic plants, restrict water flow, and harm recreation.
Is It Here Yet?
Yes. Eurasian watermilfoil has been documented throughout Washington.
Why Should I Care?
Eurasian watermilfoil forms dense mats on the water surface, interfering with recreational activities, displacing native vegetation, causing flooding, and clogging water intakes. It can infest an entire lake quickly and is a low-quality food source for wildlife. It provides poor habitat for many native aquatic species and is good habitat for mosquitos. Eurasian watermilfoil’s ability to hybridize with native northern milfoil threatens the native species’ survival.
How Can We Stop It?
Clean, drain, and dry boats and any other equipment or gear that has entered potentially infested waters. This noxious weed spreads through fragments that easily grow into new plants. Never transport aquatic plants between water bodies, and do not release aquarium plants into any water body. Eurasian watermilfoil is on Washington’s Wetlands and Aquatics Quarantine list, meaning it is prohibited to transport, buy, sell, offer for sale, or distribute Eurasian watermilfoil plants or plant parts. Eurasian watermilfoil also is listed as a Class B noxious weed in Washington, meaning it is designated for control in certain state regions.
What Are Its Characteristics?
- Roots grow into the bottom of the water body.
- Leaves grow mostly underwater and are arranged around a stem in sets of 4 (or rarely 5). Each feathery leaf has 12 or more pairs of leaflets.
- Reddish flower spikes grow a few inches above the water. Flowers are small, pinkish, and have one short leaf below each flower.
How Do I Distinguish It From Native Species?
Eurasian watermilfoil may be distinguished from native milfoils by counting the paired leaflets on each leaf. Native watermilfoils typically have fewer than twelve pairs of leaflets. Eurasian watermilfoil has at least twelve pairs and oftentimes more (fourteen to twenty-one). Additionally, when out of the water, Eurasian watermilfoil leaves will become limp, while native watermilfoil leaves remain rigid.
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