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Floating primrose-willow, courtesy KCNWCP


Infestation in King County
Courtesy KCNWCP


Close-up of flower Courtesy of Jay Sullivan


Infestation in France
(Image source: Cemagraf)


Line drawing
Courtesy USDA/NRCS Plants Database

Floating primrose-willow
Ludwigia peploides

Other common names: creeping water-primrose
Plant family: Primrose (Onagraceae)
Legal Status: Class A Noxious Weed
Year listed: 2006
Native to: Regions in South, Central, and North America, including parts of the southeastern US.

How would I identify it?
Overall: Floating water-primrose is a herbaceous, perennial wetland plant whose stems usually grow flat along the mud or water surface.

Leaves:

  • alternate
  • can vary in shape and size but are often
    lanceolate , oblanceolate  , or egg-shaped
  • during the early growth period, leaves are often round shaped
  • leaf is typically between 1-9 cm
  • leaf stem is between 2.5-3.7 cm
  • leaf veins are light green and pinnately arranged

Flowers:

  • have five, bright yellow petals
  • ten stamens
  • bright green sepals
  • petals are between 1.0-1.5 cm in length
  • occur on long stalks arising from the stem between leaves

Stems:

  • can reach a length of 3 meters long
  • roots can occur on the stem between leaf nodes

Line drawings are taken from 1,000 Weeds of North America, copyright of XID Service, Inc and used with permission. Permission granted by the author.

Where does it grow?

Floating water-primrose is an aquatic herb that grows along freshwater shorelines and sprawls across the water's surface. It tolerates water depths up to 3 meters.

How does it reproduce?

This plant reproduces mainly through plant fragmentation.
  • When a piece of stem breaks off, it develops root and will grow into a new plant.
  • It also appears to produce seeds.

What plants might floating water-primrose be confused with?
Water primrose, Ludwigia hexapetala, looks very similar, and they can be very difficult to tell apart - even for experts. Please refer to the Written Findings for more information.

Where does it occur in Washington?
Currently, floating primrose-willow has only be documented in King County. If you think you may have seen this weed, please contact your local weed control program or us at noxiousweeds@agr.wa.gov

Why is it listed as a Noxious Weed?
Floating water-primrose forms dense, fast-growing, floating mats that can:
  • Displace native submerged aquatic plants
  • Displace wetland grasses, included those used as forage for cattle
  • Reduce dissolved oxygen and pH in the water
  • Increase sedimentation, which further reduces water flow and eventually water depth
  • Increase mosquito populations by providing habitat for the larvae that mosquito-eating fish can't get to
  • Block irrigation and drainage ditches
  • Reduce accessibility of  boaters, hunters, and fishing enthusiasts

This aggressive invasive plant poses a threat to our aquatic ecosystems, and can easily spread between water systems because of its ability to grow from plant fragments. Once established, it is very difficult to control.

How do I control it?
Overall: When removing floating primrose-willow, be sure to remove as many plant fragments and roots as possible. If you use a method that will kill the plant, keep in mind that the decomposing plant will cause a drop in the dissolved oxygen (DO). Treating only a portion of the floating mat at a time, or removing dying plant tissue will help reduce this risk.

Herbicide: Please refer to the WA Department of Ecology Aquatic Herbicide page, or contact your county noxious weed coordinator.

Cultural methods: Small populations may be tarped; however, covering large populations can cause a drop in DO that can effect other plants and fish.

Mechanical methods: For small populations, you can try hand pulling or raking. For larger infestations, a mechanical hervester or rotovation might be used.

Biocontrol: None currently used.

For more information

Download our Written Findings

http://www.cemagref.fr/english/ex/hydrosystem/EVJussies/EVjussiechapo.htm

http://www.eppo.org/QUARANTINE/Alert_List/invasive_plants/Ludwigia.htm

http://plants.usda.gov/java/profile?symbol=LUPE5

 Last updated March 31, 2007