Habitat and impact
Purple loosestrife is typically found invading lakeshores, wetlands, ponds, and wet pastures and ditches. The flowers are magenta, and they are found on tall, narrow spikes from July to October. Purple loosestrife has square stems, which help to tell it apart from some of the look-alikes that grow in the same areas. In winter months, dead brown flower stalks remain with old seed capsules visible on the tips. Loosestrife's appearance is similar to fireweed and spirea and often co-habitates with garden loosestrife along King County's lakeshores and wetlands.
Purple loosestrife is a long-lived wetland perennial that can reach over 9 feet tall. Plants can produce over 2 million seeds the size of ground pepper. This plant spreads by seed and root fragmentation. Purple loosestrife is native to Europe and Asia, and was initially introduced to the northeastern seaboard of the United States in the ballast of ships in the 1800's. It has also been repeatedly and continually introduced as a garden plant. Because of the impacts to fresh and brackish wetlands across the nation, purple loosestife is targeted for control and is found on many noxious weed lists throughout the country including Washington State.
Legal status in King County, Washington
This Class B noxious weed is found throughout the State of Washington and control is required in King County. This species is also on the Washington quarantine list (known as the prohibited plants list) (external link) and it is prohibited to transport, buy, sell, offer for sale, or to distribute plants or plant parts of this species, into or within the state of Washington. It is further prohibited to intentionally transplant wild plants and/or plant parts of this species within the state of Washington.
Additional information on purple loosestrife
What to do if you find this plant in King County, Washington
Please notify us if you see purple loosestrife growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. We map all known locations of regulated noxious weeds such as purple loosestrife in order to help us and others locate new infestations in time to control them. There is an active and effective biological control program in use against purple loosestrife in Washington State and in King County and we will be able to let you know if biological control agents have been released to manage specific populations in King County.
Purple loosestrife photos - click thumbnail for larger image