LRP - Licenses

LRP - Regulations

LRP - Permits

Recreation - Statewide

Recreation - Trapping

Recreation - Fishing

Recreation - Hunting

Env. Protection - Management

Env. Protection - Emergency

Env. Protection - Resources

To sign up for updates or to access your subscriber preferences, please enter your contact information below.



 
Indian Swampweed

Indian Swampweed
(Hygrophila polysperma)

A fast-growing submerged plant that is on the federal noxious weed list in the US. It is commonly grown in the aquarium trade and could pose a threat to waterways if released.



Overview

Regulated areas of Indian Swampweed
This species is Prohibited (Red counties)

Other names for this plant include:

  • Common names: Miramar weed, dwarf hygrophila, hygro
  • Scientific names: Justicia polysperma, Hemidelphis polysperma

Ecological threats:

  • Very fast rate of growth, at one lake in Florida - spread from 0.1 to 10 acres in one year.
  • Can invade freshwater lakes, reservoirs, ponds, marshes and ditches making boating, fishing, and almost all other water activities difficult.
  • Degrades water quality by blocking the air-water interface and greatly reducing oxygen levels in the water, impacting underwater animals such as fish.
  • Greatly reduces biological diversity: vegetation mats block sunlight, preventing growth of submerged and emersed plant communities and also alter animal communities by blocking access to the water and/or reducing plants the animals depend on for shelter and nesting.

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 Indian swampweed was based upon this literature review developed by the department.

Identification

Leaves: grow opposite along the stems. They are rounded, hairy and up to three inches long with pointed tips. They range in color from green to brown to reddish.

Flowers: bluish-white to white, and have two lobes on upper lip and three lobes on lower lip. They grow from the axils where the leaves meet the stems.

Fruits & seeds: narrow capsule 6-7 mm long; 20-30 tiny flattened-round seeds.

Stems: square stems can grow up to six feet long.

Similar species: This plant could easily be confused with other aquatic species such as Ludwigia repens, Alternanthera philoxeroides, H. lacustris.

Distribution

Hygrophila_polysperma
Counties in WI where Indian swampweed has been reported (as of April 2013). Both vouchered and unvouchered reports included.

Currently, there are no reports of Indian swampweed in WI Have you seen it? Send us a report.

Control

Mechanical: Very small populations can be controlled by pulling. Physical removal should be completed before flowering and seed set. This plant can spread from fragments so care must be taken to collect and destroy all parts of the plant.

Chemical: Registered aquatic herbicides can provide some small control of Indian swampweed, though it shows greater resistance to herbicides than many other aquatic invasives. Application of aquatic herbicide requires a permit.

Photos

View Indian swampweed pictures in our photo gallery!

Resources

Sources for content:

Links for More Information

Last revised: Friday May 31 2019