Weed class: B
Year Listed: 2000
Native to: South America and South and South-Central United States
Is this Weed Toxic?:
not known to be
Why Is It a Noxious Weed?
It is an invasive aquatic species that forms extensive mats, impairing water flow and shoreline activity. It can dominate shoreline vegetation if introduced to lakes, rivers, ponds or streams. It is very difficult to control once established.
How would I identify it?
Water primrose is an aquatic perennial herb with robust, sprawling growth and showy, bright yellow flowers. Fibrous roots form from lower nodes on stems. It also produces white, hanging root-like structures.
Flowering stems are upright. Flowers are showy, yellow and have 5 bright petals, 0.6 to 1 inch (1.5 to 2.5 cm) long. Flowers are solitary on stalks that come from the leaf axils (upper angle of where leaf attaches to stem).
Leaves are alternately arranged along stems. Young leaves form rosette-like clusters. Mature leaves are willow-like in shape, up to about 4.75 inches long and are slightly hairy.
Stems are sprawling on water or mud. They lengthen and grow upright during flowering.
Fruit Seed Description
Capsules are formed that are up to 1.25 inches long and contain many small seeds.
May Be Confused With
Floating primrose-willow, Ludwigia peploides, a Class A noxious weed in Washington, looks very similar, and they can be very difficult to tell apart - even for experts. If you need help with plant identification, please contact your county noxious weed coordinator.
Where does it grow?
Water primrose is an aquatic herb which is found rooted and growing in shallow water to about 1 m deep; it is found in margins of lakes, ponds, ditches and streams. Please click here to see a county level distribution map of water primrose in Washington.
How Does it Reproduce?
Water primrose spreads by seeds and by plant fragments.
How Do I Control It?
Because herbicide availability and regulation differ between states, we recommend the Washington Department of Ecology website for information on aquatic weed management and herbicides, or contact your county noxious weed coordinator.
For More Information
See our Written Findings for more information about water primrose (Ludwigia hexapetala).