Floating Water Primrose (Ludwigia peploides)

Aquatic, plants, tier 3

History and Introduction

L. peploides is an emergent, aquatic perennial species that is native to South and Central America, parts of North America, and likely, Australia. L. peploides was introduced from the Americas to Montpellier in France in the 1830s; it has since become one of the most widespread and detrimental aquatic invasive species in that country. It was first observed in New York in 2003 in the Peconic River in Suffolk County (4). Other known sites with the plant include Artist Lake in Middle Island, Suffolk County and various locations in Kings, Queens, and Richmond counties.

Identification and Biology

The plant has showy yellow flowers with five petals on stalks attached at the leaf axils. The leaves are alternately attached (unlike the opposite leaves on the native L. palustris or water purslane) to the fleshy red stems. The leaves are glossy and dark green with a light green central midrib, and are often spoon shaped with smooth margins. Its glabrous stems creep horizontally and vertically across and through the mud and water, often ending in what looks like a rosette. Sometimes leaves can be long and lance shaped, as in the case of the emergent leaves and flowers of the plant. At each node grows adventitious roots to ensure oxygen uptake. The plant also has allelopathic abilities that can alter the oxygen levels in the water, leading to crashes and detrimental changes in the sulfide and phosphate compounds in the water.

Damage and Concern

The plant has recently been introduced in places beyond its native range in North America and is quickly becoming an aggressive invasive species in many parts of the United States. L. peploides is adaptable and tolerates a wide range of habitats where it is known to alter ecosystems both physically and chemically. The plant is known to grow to nearly impenetrable mats that can displace native vegetation, clog waterways and drainage systems, and alter navigation channels. This species also has an allelopathic ability that is a detriment to water quality throughout a given year. Dissolved oxygen, sulfide and phosphate levels can crash and make it nearly impossible for other native flora to grow; this decreases biodiversity over time. Also, the thick mats serve as a poor habitat for sensitive species. Dense matting shades out native flora and other submerged aquatic vegetation, and makes it difficult for fish and other invertebrates to safely travel through the infested waters it cohabitates. This plant grows very quickly and its dense nature has proven to also be a nuisance to fishers, boaters and recreationalists, and also provides an excellent mosquito habitat. However, fish that feed on the mosquito larvae have a difficult time navigating waters to maintain equilibrium of the habitat.

Management and Control

Manual/Mechanical: Physical control measures such as hand pulling or mechanical harvesting may be used to remove L. peploides, however, all parts of the plant reproduce from fragments so it is very important to ensure that all pieces of the plant are collected. The repeated manual removal of small infestations can be an effective method of control. On the other hand, the manual removal of large infestations may be ineffective in that L. peploides can spread from above and below ground fragments. As with any other invasive plant infestation, large occurrences are often best managed via a combination of mechanical and chemical means.

Chemical: Several herbicides have been used with reported success. A wetland safe 1-2% solution of triclopyr or glyphosate is effective at managing populations, as long as treatment is conducted prior to fruit/seed set. 2 4-D is also suitable for use, as is imazapyr and imazamox. Follow up treatment may be necessary in the following years. (4) A combination of manual/mechanical removal and chemical treatment is likely to provide the best results. Always check state, county, and local wetland regulations and the herbicide label for proper use.

Monitoring and Reporting

LIISMA is currently monitoring L. peploides as part of our Early Detection and Rapid Response (EDRR) program. As reports of the species are collected, LIISMA is dedicated to delineating and managing any early emerging infestations of the species before they become widespread. L. peploides is currently a Tier 3 species on Long Island, prioritized for early detection and containment.

Your reports matter to us – report the species to iMapinvasives or iNaturalist as soon as you detect it.