East Indian hygrophila (Hygrophila polysperma)

Also known as: polysperma, Indian swamp weed

East Indian hygrophila is a water weed that grows above and below the water surface. It could invade freshwater lakes, ponds and dams on the north coast of NSW.

Profile

How does this weed affect you?

East Indian hygrophila has the potential to become a serious weed of freshwater lakes, ponds and dams in the North Coast region of NSW. It grows quickly forming dense mats that:

• impede water flows 
• can block irrigation equipment
• reduce water quality
• outcompete native plants
• reduce habitat for fish and other native animals
• impede recreational activities such as boating, fishing, swimming
• reduce the visual appeal of waterways.

What does it look like?

East Indian hygrophila mostly grows underwater. However, it will grow above water on banks and shallow areas of waterways. Above water it can grow up to 1 m tall although mostly it reaches about 50 cm tall

Leaves are:

• bright green, brown or reddish
• 0.7–8 cm long and 0.5–2 cm wide
• oblong or oval with pointy tips
• sparsely covered in fine white hairs
• rounder and stalkless when above the water
• longer and with small leaf stalks underwater
• in opposite pairs on the stem.

Flowers are:

• bluish-white to white
• tubular with 5 fused petals towards the lower half of the flower
• 5–6 mm long
• between the leaf and the stem of the upper leaves.

Fruit are:

• a narrow capsule
• 6–7 mm long
• split lengthwise to release 15–30 seeds.

Seeds are:

• pale brown
• flattened and circular
• about 0.8 mm in diameter.

Stems are:

• round in cross section, and up to 2 m long when underwater
• square in cross-section and slightly hairy when above water.

Roots:

The roots can form on free floating plants and on the node in the mud.

Similar looking plants

East Indian hygrophila looks like:

• Hygrophila (Hygrophila costata), which has larger leaves, up to 18 cm long.
• Alligator weed (Alternanthera philoxeroides) which has white ball-like flowers on stalks and hollow stems.

Where is it found?

East Indian hygrophila grows in the Tweed River on the North Coast of NSW. It was introduced by the aquarium trade. It is also present in south east Queensland. 

It is native to South-east Asia and grows in tropical regions. It is a serious weed in the warm areas of the United States.

What type of environment does it grow in?

East Indian hygrophila can grow in water up to 3 m deep. It grows best in flowing water but can also grow in still or slow moving water. It prefers warmer climates with water temperatures from 22–28 °C and neutral to slightly acidic water. Plants cannot tolerate water temperatures below 9 °C or air temperatures below 4 °C.

East Indian hygrophila’s ability to grow in low light conditions allows it to outcompete many other aquatic plants.

Maps and records

• Recorded presence of East Indian hygrophila during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

East Indian hygrophila can grow in water up to 3 metres deep. It is adapted to low light conditions and expands rapidly where it can spread up to 4 hectares a year. It tends to grow more vigorously in flowing water.

The main method of reproduction is vegetative. The stems fragment easily and develop into new plants. Fragments can be transported by boats, fishing gear or just drift in the water to new locations. The importance of seeds in reproduction is not certain.

References

Cuda, J. P., & Sutton, D. L. (2000, January). Is the aquatic weed hygrophila, Hygrophila polysperma (Polemoniales: Acanthaceae), a suitable target for classical biological control. In Proceedings of the X International Symposium on Biological Control of Weed Risk Assessment for Hygrophila polysperma Ver (Vol. 1, pp. 4-14).

EPPO (2017). Pest risk analysis for Hygrophila polysperma. EPPO, Paris. 

Grantley, J., McPherson, F. & Petroeschevsky, A. (2009). Recognising Water Weeds: Plant Identification Guide Aquatic. Industry & Investment NSW.

Mikulyuk, A. & Nault, M. (2008). CABI Invasive species compendium online data sheet: Hygrophila polysperma (Indian swampweed). Retrieved 21 January 2021 from: https://www.cabi.org/isc/datasheet/28135

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved January 2021 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Hygrophila~polysperma

More information

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Control

Successful weed control relies on follow up after the initial efforts. This means regularly looking for any new plants or plant fragments and controlling them. Using a combination of control methods is usually more successful.

To manage East Indian hygrophila:

• seek advice from a local council for the best control strategies for your situation
• act quickly to control new infestations.

Physical

Small infestations can be removed by hand. Sites will need to be checked regularly as any small fragments left behind will reshoot.

Disposal

Contact your local council for advice on how to dispose of this plant.

Chemical

East Indian hygrophila can be spot sprayed. Only use herbicide products that have label approvals for aquatic use.

Herbicide options

See Using herbicides for more information.

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: One part product to 50 parts water
Comments: Spot spray
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: One part product to 9 parts water
Comments: Splatter gun
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
Central West	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
Greater Sydney	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
Hunter	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
North Coast Exclusion (eradication) zone: Bellingen Shire LGA, Clarence Valley LGA, Lord Howe Island, Nambucca Valley LGA, Port Macquarie-Hastings LGA. Core infestation (containment) zone: Ballina Shire LGA, Byron Shire LGA, Coffs Harbour City LGA, Kempsey Shire LGA, Kyogle Shire LGA, Lismore City LGA, Richmond Valley LGA, Tweed Shire LGA.	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers should mitigate the risk of the plant being introduced to their land. A person should not buy, sell, move, carry or release the plant into the environment. Exclusion zone: Notify local control authority if found. Land managers should eradicate the plant from the land and keep the land free of the plant. Core infestation: Land managers should mitigate spread of the plant from their land. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
North West	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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Reviewed 2023