Floating Primrose-Willow
Ludwigia peploides
Washington State Classification
Class A — Eradication Required Statewide
It forms dense, fast-growing, floating mats that can displace native aquatic plants and wetland grasses.
Quick Reference
Identification
Growth Habit
It is an herbaceous, perennial wetland plant whose sprawling stems usually grow flat along mud or a water surface. Water primrose, Ludwigia hexapetala, a Class B noxious weed in Washington, looks very similar and they can be very difficult to tell apart.
Leaves
They are alternately arranged, clustered and vary in shape and size. They can be lance-shaped to egg-shaped and are up to about 3.5 inches long. Leaf bases tapers to a stalk that ranges from 1-1.5 inches long. Leaves are hairless and have smooth margins.
Flowers
Flowering stems are floating or lying on the ground. Flowers have five bright yellow petals, 0.4 to 0.6 inches (1 to 1.5 cm) long. The flowers occur on long stalks arising from the leaf axils (upper angle of where leaf attaches to stem).
Fruit & Seeds
Capsules contain many small seeds (1mm in size).
Impact
It forms dense, fast-growing, floating mats that can displace native aquatic plants and wetland grasses. Mats can also lower dissolved oxygen and pH of the water, reduce water quality for wildlife and increase sedimentation.
Ecology & Spread
Habitat
Floating water-primrose grows along freshwater shorelines and sprawls across the water's surface. It typically inhabits margins of lakes, ponds, ditches and streams. It can tolerate water depths up to around 10 feet. Please click here to see a county level distribution map of floating primrose-willow in Washington.
Spread Mechanisms
Reproduction
Floating water primrose reproduces mainly through plant fragmentation. When a piece of stem breaks off, it develops roots and will grow into a new plant. It also appears to produce viable seeds.
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