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 on the north coast 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
  • 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, 2017-2021)
    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.

  • Estimated distribution of East Indian hygrophila in NSW (Map: NSW Noxious Weed Local Control Authorities, 2010)
    Map shows weed distribution and density estimated by local council weeds officers in 2010.

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 requires 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 tackle 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

Contract 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

WARNING - ALWAYS READ THE LABEL
Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website www.apvma.gov.au

See Using herbicides for more information.


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


PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
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 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*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
Greater Sydney Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
Hunter Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
North Coast
Exclusion zone: all waters in the region excluding the core infestation area of Richmond Valley Council, Ballina Shire Council, Lismore Council, Kyogle Council, Byron Shire Council and Tweed Shire Council.
Regional Recommended Measure*
Whole region: The plant or parts of the plant should not be traded, carried, grown or released into the environment. Exclusion zone: The plant should be eradicated from the land and the land kept free of the plant. Land managers should mitigate the risk of the plant being introduced to their land. Core infestation area: Land managers should reduce impacts from the plant on priority assets.
North West Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. 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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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW DPI Biosecurity Helpline on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2021