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Asian marshweed

(Limnophila sessiliflora)

Photo of Asian marshweed
Photo credit: Vic Ramey, University of FL/IFAS for aquatic & invasive plants

An aquatic perennial herb that can exist in a variety of aquatic habitats. It is fast-growing and can regrow from fragments. When in high densities it is able to shade out other submerged aquatic species.

Overview

Other names for this plant include:
  • Common names: Ambulia
  • Scientific names: Ambulia sessiliflora, Hottonia sessiliflora, Stemodia sessiliflora, Terebinthina sessiliflora, Stemodiacra sessiliflora
Ecological threat:
  • It invades freshwater lakes, reservoirs, ponds, marshes and slow-flowing streams and rivers making boating, fishing, and almost all other water activities difficult.
  • A dense growing habit from the bottom of the waterbody to the surface can crowd out native aquatic vegetation.
  • A competitive aquatic plant that can tolerate low light levels and grow in water up to 12 feet deep.
 Overview map of prohibited classification in WI
Prohibited (red) counties

Classification in Wisconsin: Prohibited

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for Asian marshweed was based upon this literature review [PDF] developed by the department.

Identification

Leaves: Above water, the leaves are dark green, more-or-less lance-shaped; in whorls of 5-8 leaves about the stem. Margins appear to be torn irregularly. Submersed leaves are finely divided and feathery, segments opposite.

Flowers: Small and solitary in leaf axils in the uppermost parts of the stems, above the water. Five fused petals are 5-10 mm long and blue, violet, pink or lavender, upper lip white or pink.

Fruits & seeds: Forms capsules, ellipsoid, with up to 150 seeds.

Roots: From stem nodes, numerous.

Similar species: Vegetation appears similar to other submerged aquatic plants upon first glance, particularly fanworts.

Distribution

Currently, there have been no reports of Asian marshweed in Wisconsin. Have you seen it? Send us a report.

Control

Mechanical: Removal by hand or machine is a practical control method only for small areas or when numbers are low. Plants can regrow from stem fragments so care must be taken to gather and destroy all plant parts if removing.

Chemical: Registered aquatic herbicides can provide temporary control of Asian marshweed in small scale applications. 2,4-D apparently has been effective. Application of aquatic herbicide requires a permit.

Photos

View Asian marshweed pictures in our photo gallery!

Resources

Sources for content: Links for more information: