Species include:
- Creeping water primrose (Ludwigia peploides) also known as: floating primrose or floating primrose willow.
- Water primrose (Ludwigia hexapetala) also known as: Uruguay waterprimrose.
Invasive water primroses are floating aquatic plants that form fast growing, floating mats. These dense mats can completely cover the water’s surface displacing native plants, reducing wildlife habitat, and impeding water recreation. Their mats are so thick that a person can even walk across them!
For detailed information, download the Invasive Water Primrose Best Management Practices factsheet.
Description:
| Life Cycle: | Perennial (life cycle lasts more than one year) |
| Early Detection and Rapid Response species: | Yes |
| Height: | Submerged stems can grow up to 6 feet (2 meters) long. |
| Leaf Description: | Both species have bright green leaves are glossy and grow alternately along the stem. Leaves on stems without flowers are oblong. Leaves on flowering stems are lance-shaped. |
| Fruit & Flower Description: | Bright yellow flowers bloom on short stems above the water’s surface. Flowers have five petals. Flowers produce a small seed capsule that contain 40 to 50 seeds. |
| Bloom Time: | July to September |
How they spread:
- Invasive water primroses spread by seed, root and plant fragmentation, making them difficult to control.
- Stem fragments are buoyant and can be transported to new waterbodies by waterfowl and flood events. Plant fragments can also hitch a ride on boats and other water recreational equipment.
Habitat:
- These plants are found in shallow, slow-moving freshwater environments such as wetlands, lakes, ponds, and slow-flowing rivers.
- They can grow in waterbodies up to 10 feet (3 meters) deep and can grow on land once water levels recede.
Impact:
- Invasive water primroses form dense mats that completely cover the water’s surface.
- These mats displace native plants, reduce wildlife habitat, and impede water recreation such as boating, swimming, and fishing.
- Decaying plant material also causes rapid sedimentation and lowers oxygen levels, killing fish.
What we’re doing about them:
- Both species of invasive water primrose are priority species for the Tualatin SWCD. As such, our Invasive Species Program has been actively monitoring and treating them throughout the watershed.
- If identified within Washington County, a specially trained crew can come out and survey for them. If found, the crew will treat the infestation for free.
What you can do about them:
- If you think you’ve found either species of invasive water primrose in Oregon, please report it to the Oregon Invasive Species Hotline.
- Cultural: Prevention is the best control for invasive water primroses. When choosing aquatic plants, consider native aquatic plants.
- If you are removing unwanted aquatic plant material, dispose of it in a tied plastic bag in the garbage rather than dumping it in nearby waterways.
- Manual: Small patches can be controlled with diligent hand pulling. This takes persistent and careful effort.
- Place any removed plant material in a tied plastic bag in the garbage. Several years of monitoring are required to ensure the infestation does not return.
Look-alikes:
Water purslane (Ludwigia palustris) is a Pacific Northwest native that shares similar characteristics as the invasive water primroses. Water purslane leaves grow opposite along the stem whereas both invasive water primroses’ leaves grow alternately. Also, water purslane has smaller leaves and small, green-colored flowers.
Noxious Weed Listing:
| State of Oregon: | Class B and T |
| State of Washington: | Class A (Ludwigia peploides) Class B (Ludwigia hexapetala) |
More Resources:
- University of California, Weed Research and Information Center: Waterprimroses