Water Primrose Species

General Information

Water primroses are non-native perennial herbs found creeping along the shoreline, floating on the water surface, or growing upright. They are robust plants with bright yellow, showy flowers and willow-like leaves. They are non-native species originally from South America that have been introduced into Europe and North America. In Washington, L. hexapetala has established in the drainage ditches in the Longview/Kelso area of southwestern Washington. King County weed staff also discovered small populations of this species and also L. peploides in King County. We speculate that at one time, nurseries sold these species in Washington as aquatic garden plants. These species are very invasive and aggressive and form very dense mats of vegetation. Washington lists L. hexapetala as a Class B noxious weed and L. peploides as a Class A noxious weed. The Washington Department of Agriculture lists both species on its quarantine list that prohibits their sale, trade, or transport in Washington.

Growth Habit

These non-native primrose species grow in dense mats along shorelines and out into the water. They favor the margins of lakes, ponds, ditches, and streams. They bloom throughout the summer. This photograph shows L. hexapetala growing along a ditch bank in Longview. Both species reproduce by seeds and by plant fragments.

Management

The Longview Diking District uses mechanical methods to remove water primrose and other noxious plants from the canals and ditches in Longview/Kelso. Other methods such as cutting, covering with opaque materials, and using the aquatic herbicide (Rodeo®) may be effective. It is unlikely that grass carp would find water primroses palatable.

Identification

You can identify non-native water primrose species by their sprawling growth habit and showy yellow flowers.

Look for the following characteristics

• Bright, yellow flowers; normally with 5 petals
• Alternately-arranged, slightly hairy, willow-like leaves
• Dense sprawling, tangled mat of vegetation