Ludwigia Ludwigia Ludwigia Ludwigia Event Ludwigia Flower Ludwiga

Water Primrose, or Floating Primrose Willow
Ludwigia peploides


Origin: Tropical and subtropical America

Background: Water primrose, known commonly by its scientific name Ludwigia peploides, is an invasive aquatic perennial that has invaded many waterways, most notably throughout France, and is now an emerging concern in the United States. In 2003, L. peploides was first observed on the Peconic River. Prospect Park in Brooklyn is the only other site on Long Island where it has been found growing wild.

This plant’s ability to quickly reproduce, coupled with the damaging effects it has on native species, prioritizes the removal of L. peploides from the Peconic Estuary System. Since the arrival of the water primrose in the Peconic River, recreation in Peconic Lake has been impaired—the dense mats of vegetation make boating and fishing nearly impossible.

Habitat: Ditches, riverbanks, ponds, slow moving streams, and along margins of lakes and reservoirs. The major growth requirement for this species is submerged roots.

Ecological Threat: The water primrose poses many ecosystem threats due to its rapid and extensive growth. French studies indicate that Ludwigia species are able to double their biomass in 15 to 20 days in slow-flowing waters and in about 70 days in rivers, allowing for the rapid destruction of native ecosystems. This species can quickly block waterways, interfering with human uses of water systems such as boating, swimming, and fishing. Water primrose also reduces biodiversity and degrades water quality by decreasing pH and dissolved oxygen content. Because its leaves are above the water surface, Ludwigia does not add much oxygen, if any, to the water column and shades out submerged plants below that could add oxygen to the water column.

Description and Biology:

Plant: Floating aquatic perennial herb of the Evening primrose, or Onagraceae, family, sometimes forms mats. Flower bearing stems are weakly upright with lance-shaped leaves. Stems have little to no hair. The stems are purple in color and are rooted, but most of the stem floats on the surface of the water.

Leaves: Leaves occur alternately on the stem, and are net-veined (as opposed to grass-like leaves which are parallel veined). The leaves are elongate with smooth outer margins, and have long petioles.

Flowers, fruit, and seeds:Flowers are approximately one inch wide with five petals, and occur on stalks 1 to 5 cm long. Foliage may differ according to growing area. The fruit is a cylindrical capsule containing many seeds, which are yellowish, oval, and less than 1 mm long.

Dispersal: Fragmentation of stems is the main mode of dispersal. The role of seeds in dispersal has not been studied extensively, but seeds have been germinated in the laboratory.

Identification: Ludwigia peploides may be mistaken for swamp loosestrife (Decodon verticillatus) when not in flower. The two plants can be distinguished from one another by their leaves. Ludwigia has leaves that alternate up the stem, while swamp loosestrife has leaves that occur opposite one another.

Prevention and Control:

Because Ludwigia reproduces by fragmentation, it is extremely important to fully and carefully remove the entire floating strand. Harsh removal methods are not suggested due to the potential of breaking the stands into smaller fragments. Hand-pulling has proven to be the most effective and control technique in the Peconic River. Pulled and removed strands and patched should be disposed of in NYSDEC Invasive Species Disposal Stations or in the garbage.

In 2006, The Peconic Estuary Program, in collaboration with the New York State Department of Environmental Conservation, Suffolk County, The Nature Conservancy, Peconic Lake Estates Civic Organization, Fresh Water Anglers of Long Island, Inc., the US Environmental Protection Agency, and Long Island Bassmasters, initiated a multi-year monitoring and eradication effort in an attempt to rid the species from the Peconic River and prevent spreading to other Long Island waters. Since the initiation of the eradication effort in the spring of 2006, over 438 volunteers have spent over 2360 hours hand-pulling nearly 130 cubic yards of Ludwigia.

Although Ludwigia’s spread is currently contained, maintenance pulls and monitoring are still necessary to ensure the species does not resurge and once again spread throughout the river. Funding for this effort was provided by a NYSDEC Aquatic Invasive Species Eradication Grant and a Corporate Wetland Restoration Partnership (CWRP) grant.

NYSDEC has installed several invasive species disposal stations throughout New York State and along the Peconic River. Boaters and fishermen are encouraged to clean vegetation off boat trailers to limit transport of invasive species. Recreators are also encouraged to place removed Ludwigia in the designated stations.

Photo by: Chart Guthrie, NYSDEC

In 2009 NYSDEC and Peconic Estuary Program installed 5 educational interpretive signs along the Peconic River to educate fishermen, boaters and the general public about the successful Ludwigia eradication effort, the ecological threat this invasive species poses, and the importance of maintaining the project’s success.

Photo by: Laura Stephenson, NYSDEC/PEP

Native Alternatives: Unfortunately, the water primrose is still being sold as a decorative species. Never purchase or plant Ludwigia peploides. Try a native alternative, such as marsh marigold (Caltha palustris) instead, and help protect the Peconics!



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