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 infest wetlands, marshes, and streamsides.
Description:
| Life Cycle: | Perennial (life cycle lasts more than one year) |
| Early Detection and Rapid Response species: | Yes |
| Height: | Up to 10 feet (3 meters) |
| Leaf Description: | Lance-shaped leaves are arranged in whorls An arrangement of leaves that radiate from a single point and wrap around the plant’s stem., 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 be up to a foot long. Each plant can have upwards of 50 flower spikes. |
| Bloom Time: | July to September |
Habitat:
- Establishes dense thickets in wet areas such as wetlands, marshes, and riparian areasAreas that are directly adjacent to flowing streams, creeks, or rivers..
Impact:
- An aggressive invader which quickly displaces native vegetation.
- A mature plant can produce up to 2.7 million tiny seeds annually, which spread by water, wind, wildlife, and humans. It also spreads by stem fragmentation.
- Large infestations result in decreased waterfowl and songbird habitat.
What we’re doing about it:
- Purple loosestrife is categorized as 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 at no cost to you.
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. Make sure to remove the entire root system and throw it away in a 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 produces pink to purple flowers but Douglas spirea’s flowers are more wooly 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