Also known as: Purple lythrum, spiked loosestrife
Purple loosestrife’s showy, upright clusters of purple flowers give it the nickname – the beautiful killer. It is commonly planted as an ornamental species, but can quickly overtake wetlands, marshes, and streambanks.
Description:
| Life Cycle: | Perennial (life cycle lasts more than one year) |
| Early Detection and Rapid Response species: | Yes |
| Height: | Up to 6.5 feet (2 meters) tall |
| Leaf Description: | Lance-shaped leaves are arranged in whorlsWhorls An arrangement of leaves that radiate from a single point and wrap around the plant’s stem. of three, opposite, or alternate along the stem. |
| Fruit & Flower Description: | Flowers are usually magenta but can be light pink or white. Tiny flowers are arranged on long showy spikes that can grow up to 3 feet (1 meter) long. Each plant can have upwards of 50 flower spikes. Seeds are extremely small but are carried in oblong-shaped seed capsules. Mature plants can produce 2.7 million seeds annually. |
| Bloom Time: | July to September |
Habitat:
- Purple loosestrife prefers areas with wet soils and lots of sunlight.
- It establishes dense thickets in wet areas such as wetlands, marshes, and riparian areasRiparian Areas Areas of land that occur along the edges of rivers, streams, lakes, and other bodies of water..
Impact:
- It crowds out native vegetation that is needed by wildlife for food and shelter.
- Its dense root system change the hydrology of wetlands.
- Its tiny seeds are easily spread by water, wind, wildlife, and humans. It also spreads by stem fragmentation.
What we’re doing about it:
- Purple loosestrife is a priority species for the Tualatin SWCD. As such, our Invasive Species Program has been actively monitoring and treating it throughout the watershed.
- If identified within Washington County, a specially trained crew can come out survey for purple loosestrife. If found, the crew will treat the infestation for free.
What you can do about it:
- If you think you’ve spotted purple loosestrife, please report it to the Oregon Invasives Species Hotline.
- Individual plants and small clusters can be hand-pulled, using care not to scatter the seeds if treating after flowering has begun.
- Removing flowers early in the blooming season can help prevent seed dispersal. Avoid cutting flower spikes with mature seed capsules
- Make sure to remove the entire root system and throw any plant material away in a tied plastic bag in the trash— not your yard waste bin or home compost.
Look-alikes:
Fireweed (Chamaenerion angustifolium) is a native alternative to purple loosestrife. It has similar magenta flowers but has red stems which differentiate it from purple loosestrife.
The Pacific Northwest native Douglas spirea (Spirea douglasii) also looks similar to purple loosestrife. Both plants produce pink to purple flowers but Douglas spirea’s flowers are more woolly in appearance.
Noxious Weed Listing:
| State of Oregon: | Class B |
| State of Washington: | Class B |
More Resources:
Download the Purple Loosestrife Best Management Practices Factsheet
- Pacific Northwest Weed Management Handbook: Purple lythrum
- University of California, Weed Research & Information Center: Purple loosestrife