Purple Loosestrife (Lythrum salicaria)


Common names:

Purple loosestrife, purple lythrum, spiked loosestrife

Scientific Name:

Lythrum salicaria


Purple loosestrife is an herbaceous wetland plant in the Lythraceae (loosestrife) family. It has showy, upright clusters of purple flowers. The stem is 4 to 6 sided, with leaves that are opposite and sometimes have smaller leaves coming out at the nodes. It was introduced through the ballast of ships in the 1800s and is also sometimes introduced through plant trades and sales.

Life cycle:


Height of mature plants

Up to 10 feet tall (but usually closer to 3-5 feet tall)

Flower color:

pink to purple

Bloom time:

July to September


Purple loosestrife can be confused with native spirea (Spirea douglasii) or native fireweed (Chamerion angustifolium). One of the obvious differences is the leaves; purple loosestrife leaves are arranged in an opposite pattern, while the look alikes have alternating leaves.


Purple loosestrife grows in wet areas such as wetlands, streamsides, and marshes.


Purple loosestrife grows vigorously in wet areas and can become dense, crowding out other vegetation. A mature plant can produce up to 2.5 million tiny seeds, which can spread by water and and birds. However, it can also reproduce by stem fragments. Areas that are heavily infested with this plant see a reduction in quality habitat for waterfowl and song birds.

Noxious Weed Listing:


North Africa, Asia, Australia, and Europe


Oregon Noxious Weed Profile
Washington Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium
Global Invasive Species Database


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