Uruguay water primrose

Ludwigia hexapetala · Aquatic plants

Flowers or seeds · Photo: armeria / CC BY

InvasiveFloating-leaf

Also called Large flower primrose willow, Ludwigia grandiflora ssp. hexapetala, Ludwigia grandiflora, Water primrose

State noxious weed listing

Oregon: B list (T)

How to identify Uruguay water primrose

Bright yellow flowers about 1 inch or more across with 5 or 6 petals
Glossy willowlike leaves on floating stems that later turn upright
White spongy floating roots at the stem joints
Hairy stems and leaves on upright shoots

Similar plants

Floating primrose willow has smaller flowers and rounder floating leaves, and native water purslane has tiny flowers without petals.

Growth profile

Growing season	New shoots form floating rosettes in spring, growth surges in warm summer water, flowers bloom from June to October, and stems die back in winter while rooted crowns and stem pieces survive.
Starts growing	About 50 to 55 F water; fastest above 70 F
Light	Needs full sun
Depth	Moist shoreline to about 10 feet
How it spreads	Stem fragments, rhizomes and seeds
Habitat	Shallow ponds, sloughs, ditches and lake margins over soft mud in low elevation western Oregon.

Why it matters in a lake

Forms dense floating and upright mats that choke shallow water, cut oxygen and raise mosquito habitat. Tiny stem pieces root and start new plants; it is a listed noxious weed in Oregon.