Hygrophila polysperma (Roxb.) T. Anderson

Common Name: Indian swampweed

Synonyms and Other Names:

Hygro, East Indian hygrophila, Indian swampweed, Miramar weed, East Indian swampweed, Dwarf hygrophila, Justicia polysperma (Roxb.), Hemidelphis polysperma (Roxb.) Nees in Wall.

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Identification: Stem/Roots: Hygrophila polysperma is a spiny dicotyledon plant. It is primarily a submersed rooted plant, but can be emersed in shallow areas where it produces smaller, darker leaves (Cuda and Sutton 2000). Stems are creeping ascendant, brittle, and easily fragmented, and are 6 feet or longer (Ramey 2001). The emersed stems can be squarish.

Leaves: It has elliptical leaves that are up to 8 cm long and 2 cm wide, and taper to a sharp point (Langeland and Burks 1999). Attachment of leaves is sessile, with the bases joined at the nodes by ciliated flanges of tissue. The leaf arrangement is opposite.

Flowers: Flowers are small and solitary in the uppermost leaf axils, and are nearly hidden by leaves. The calyx is 5-lobed, the corolla is bluish-white and 2-lipped, and there are 2 fertile stamens.

Fruit/Seeds: The fruit is a narrow capsule, which splits lengthwise to release tiny round seeds.

Look-a-likes: Ludwigia repens creeping primrose-willow, Alternanthera philoxeroides alligatorweed, and Hygrophila costata lake hygro. The key difference is that H. polysperma is mainly submersed.

Size: Stems 6 feet or longer.

Native Range: India, Malaysia, Bangladesh, Bhutan, Nepal, Cambodia, Laos, Myanmar, Thailand, and Vietnam (Angerstein and Lemke 1994, Nault and Mikulyuk 2009).

Nonindigenous Occurrences: It occurs in Australia (Romanowski 2011), Kasterer Muhlenerft in Germany (Hussner et al. 2007), and Tamaulipas in Mexico (Mora-Olivo et al. 2008). In the US, H. polysperma occurs in Florida (USDA NRCS 2014), South Carolina (SC DNR 2010), Texas (Angerstein and Lemke 1994), and Virginia (USDA NRCS 2014).  Hygrophila polysperma has been documented near the Catskills region, New York (Harman 2011).

This species is not currently in the Great Lakes region but may be elsewhere in the US. See the point map for details.

Table 1. States/provinces with nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Hygrophila polysperma are found here.

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
AL199620202Middle Chattahoochee-Walter F; Mobile-Tensaw
FL1965202324Alafia; Apalachee Bay-St. Marks; Caloosahatchee; Crystal-Pithlachascotee; Econfina-Steinhatchee; Florida Southeast Coast; Hillsborough; Kissimmee; Lake Okeechobee; Little Manatee; Lower Ochlockonee; Lower St. Johns; Lower Suwannee; Manatee; Myakka; Oklawaha; Peace; Santa Fe; Sarasota Bay; Tampa Bay; Upper St. Johns; Waccasassa; Western Okeechobee Inflow; Withlacoochee
MS201020101Upper Tombigbee
TX196920215Caddo Lake; Elm-Sycamore; Middle Guadalupe; San Marcos; Upper San Antonio
VA195719571Lower James

Table last updated 5/30/2024

† Populations may not be currently present.

Ecology: Hygrophila polysperma is a wetland plant that can occur as a submerged or an emersed plant. It inhabits lakes, streams, marshy areas, ditches, and rice-fields (de Thabrew 2014). This species can grow in water at depths up to 3 m and on stream banks as an emersed plant (Nault and Mikulyuk 2009). Hygrophila polysperma can inhabit habitats with a variety of environmental conditions. It favors warmer waters of 18-30°C but can tolerate water temperatures as low as 4°C (Kasselmann 1995, Ramey 2001, Rixon et al. 2005, US EPA 2008). It grows in waters with pH of 6.5-7.8 (Doyle et al. 2003, Spencer and Bowes 1985) and water hardness of 30-140 ppm (Nault and Mikulyuk 2009). This species has low light saturation and compensation points, so it is capable of photosynthesizing in low light levels (Doyle et al. 2003). Hygrophila polysperma exhibits low seasonality and can maintain shoot biomass year round (Spencer and Bowes 1985). Growth rate is dependent on water temperature and daylight (Nault and Mikulyuk 2009), and can increase dramatically in the presence of nutrient inputs (Sutton and Dingler 2000). This species can draw CO2 from both the water and atmosphere (Doyle et al. 2003).

In North America, H. polysperma has a specific life cycle, starting with a rooted stage in hydro-soil in dense stands of shoots, some with large leaves reaching up to the canopy, and some emergent ones with smaller leaves. Shoots on moist banks are very small, and resemble the submerged form after banks are flooded. Shoots begin elongating in March as the water temperature rises, then they reach the surface in late spring. In summer, they break off into mats and float away, and take root as soon as they come into contact with soil. The whole shoot of the plant breaks off near the root crown in August and forms very dense floating mats, which can sink piece by piece, or all at once to form a new colony; new shoots regrow from the roots, and they grow slowly in winter (Hall et al. 2003).

Means of Introduction: Hygrophila polysperma has a moderate probability of introduction to the Great Lakes (Confidence level: High).

Potential pathway(s) of introduction: Unauthorized release, hitchhiking/fouling

Hygrophila polysperma is listed as a Federal Noxious Weed and is prohibited in Illinois and Minnesota (Great Lakes Panel on Aquatic Nonindigenous Species, 2012), but can be ordered on the internet (Kay and Hoyle 2001). Surveys conducted by Rixon et al. (2005) found that H. polysperma was available for purchase in 25% of the pet and aquarium stores surveyed near Lakes Erie and Ontario. Maki and Galatowitsch (2004) had evidence that H. polysperma is available for purchase from vendors across the U.S. with delivery service to Minnesota. In addition, it is sometimes sold under the incorrect name of Alternanthera sessilis (Maki and Galatowitsch 2003). The availability of and accessibility to H. polysperma in the aquarium industry may increase its potential to be introduced to the Great Lakes; after purchase and usage for aquariums, owners may dispose of the plant into waters connected to the Great Lakes basin.Hygrophila polysperma was cultivated in Ohio at the end of WWII by an aquarium dealer (Reams 1953), but there is no indication that this species is still cultivated there.    

Hygrophila polysperma spreads via vegetative fragmentation. Hygrophila polysperma has a high regrowth potential from stem fragments (Spencer and Bowes 1985). It can get entangled and be transported to the Great Lakes on boats and recreational gear. Hygrophila polysperma fragments can also be dispersed by water; however, because this species does not currently occur near waters connected to the Great Lakes basin, it is unlikely that fragments will be transported by water to the Great Lakes.

Status: Established in North America, but not including the Great Lakes.

Hygrophila polysperma has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: High).

This perennial aquatic plant inhabits freshwater lakes and streams. Rixon et al. (2005) predict that H. polysperma has the potential to overwinter in the Great Lakes. This species can tolerate temperatures of 4°C (Kasselmann 1995) to 30°C (GISD 2005). It inhabits waters at depths of 1.5-2.0 m and can photosynthesize in lower light levels than most native aquatic plant species (Spencer and Bowes 1984). Hygrophila polysperma is able to draw carbon dioxide from both water and atmosphere (Doyle et al. 2003). This species grows best at pH 5-7 (Spencer and Bowes 1985). Its nonindigenous occurrences in the U.S. have somewhat similar climates and abiotic conditions as the Great Lakes. Suitable habitats for H. polysperma are likely somewhat available in the Great Lakes. The effects of climate change on the Great Lakes, such as warmer water temperatures and shorter duration of ice cover, may improve habitat suitability for this species.
    Although it can produce seeds, Hygrophila polysperma primarily propagates vegetatively, and forms many adventitious roots at nodes along the stems, which aids the rooting of dispersed fragments (Spencer and Bowes 1985). A recent study found that non-native populations in the U.S. and Mexico were very genetically similar, suggesting that Hygro was propagated clonally in its invasive range (Mukherjee et al. 2016). Hygrophila polysperma has a high regrowth potential from stem fragments (Spencer and Bowes 1985). Growth rate of H. polysperma is enhanced by higher flow rates (Van Dijk et al. 1986). It can spread rapidly to form dense monoculture stands; it expanded from 0.04 ha to over 0.41 ha in one year (Vandiver 1980). Hygrophila polysperma has spread extensively in the southeastern U.S. and parts of Mexico.
    Hygrophila polysperma may outcompete native species. When H. polysperma was experimentally grown with Ludwigia repens, L. repens experienced slower growth rate, produced fewer and shorter stems, and produced fewer branches per stem than when grown without the presence of H. polysperma (Doyle et al. 2003). In addition,  H. polysperma produces fewer but longer highly branched stems when grown with L. repens. This species forms dense monocultures that exclude native plants and is a superior competitor because of its low requirements for light as well as its rapid growth (GISD 2005, Nault and Mikulyuk 2009, Spencer and Bowes 1985, Robinson 2003).

Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...


Hygrophila polysperma has the potential for moderate environmental impact if introduced to the Great Lakes.

Hygrophila polysperma can have negative impacts on native species and the ecosystem. This species grows quickly into dense mats that can reduce light availability and dissolved oxygen levels. It shades out native submerged plants (Ramey 2001) and can displace native plants when it occupies the entire water column. Surveys conducted shown that H. polysperma can spread rapidly to become one of the most abundant species where it has been introduced, displacing native species (Owens et al. 2001, Vandiver 1980). In Texas, it rapidly spread to occupy 20% of the Comal River displacing native macrophytes (Doyle et al. 2003). When H. polysperma was grown with Ludwigia repens, L. repens exhibited slower growth rates compared to when grown alone, suggesting that H. polysperma has superior competitive abilities (Doyle et al. 2003). Hygrophila polysperma can create anoxic conditions once decomposition occurs (Owens et al. 2001, Robinson 2003). The dense mats of H. polysperma can trap sediments and reduce water flows (Robinson 2003).

Hygrophila polysperma has the potential for high socio-economic impact if introduced to the Great Lakes.

Dense mats of Hygrophila polysperma can provide breeding grounds for mosquito populations. The mosquito, Coquillettidia perturbans, reportedly attaches to submerged roots of H. polysperma to complete development and is a vector of eastern and western equine encephalomyelitis (Cuda and Sutton 2000). This species is problematic, as it clogs irrigation and flood control canals and interferes with water control pumping stations (Cuda and Sutton 2000). It is costly to control H. polysperma infestations; in 2006, Florida spent $14,000 to control H. polysperma covering 206 acres (FL DEP 2007). Infestations of H. polysperma make navigation difficult and inhibit recreational use (Cuda and Sutton 2000, Robinson 2003). The present of widespread, dense mats of H. polysperma can hinder fishing, boating, and swimming activities, causing a reduction lake property value (Robinson 2003).

Hygrophila polysperma has the potential for moderate beneficial impact if introduced to the Great Lakes.

In India, H. polysperma seeds are used as a medicine (Spencer and Bowes 1985). Hygrophila polysperma is commercially valuable as an ornamental plant and aquarium species (Cuda and Sutton 2000). Hygrophila polysperma is advertised for beginner aquarists because it is hardy and easy to grow. This species may increase water clarity when abundant (Osceola County 2012).

Management: Regulations (pertaining to the Great Lakes region)

This species is prohibited in parts of the Great Lakes including Chicago, Illinois, and Minnesota. It is not prohibited in Indiana, Michigan, New York, Ohio, Ontario, Pennsylvania, Quebec, or Wisconsin (Great Lakes Panel on Aquatic Nuisance Species 2012). Hygrophila polysperma is listed as a Federal Noxious Weed, so it is illegal to import, sell, or purchase this species in the United States (APHIS 2012).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.


Triploid grass carp (Ctenopharyngodon idella) is used in combination with mechanical or chemical methods in Florida, but there are no records indicating that it was successful in eliminating H. polysperma (Cuda and Sutton 2000).

Mechanical harvesters are ineffective against H. polysperma and may encourage its spread by vegetative fragmentation (Cuda and Stutton 2000).

Invert herbicide applications of endothal (7-oxabicyclo [2,2,1] heptane-2,3, dicarboxylic acid) plus copper have not shown to be effective in eradicating H. polysperma (Spencer and Bowes 1985).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: Many thanks to University of Florida, Center for Aquatic and Invasive Plants, for the superb photographs.

It is now causing problems in areas formerly dominated by Hydrilla (Cuda and Sutton 2000).

References (click for full reference list)

Author: Jacono, C.C., E. Baker, and J. Li

Contributing Agencies:

Revision Date: 4/4/2019

Citation for this information:
Jacono, C.C., E. Baker, and J. Li, 2024, Hygrophila polysperma (Roxb.) T. Anderson: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=225&Potential=Y&Type=2&HUCNumber=, Revision Date: 4/4/2019, Access Date: 5/30/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.