Purple Loosestrife
Lythrum salicaria

This Class B noxious weed is found throughout the State of Washington and control is required in King County. Purple loosestrife is sometimes sold as a garden ornamental. This plant is on the Prohibited Plants List (external link), and it is illegal to buy, sell, transport or offer this plant for sale in the state of Washington.

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.

There is an active and effective biological control program in use against purple loosestrife in Washington State and in King County.

Purple loosestrife photos - click thumbnail for larger image