Water mimosa (Neptunia oleracea)
Water mimosa is a perennial aquatic plant that grows on the banks of waterways with its stems growing out over the surface of the water. It outcompetes native plants and reduces food and habitat for fish and other aquatic animals.
Profile
How does this weed affect you?
Water mimosa is a weed of waterways. It forms thick mats on the water’s surface and:
- smothers native vegetation
- reduces water quality by reducing light and oxygen levels
- kills fish and native plants living in the water
- limits water flow, increasing the risk of floods
- limits access to water for recreational use.
What does it look like?
Water mimosa plants send down tap roots into the bank, while the stems grow out over the surface of the water. As they age they develop a spongy covering. The leaves are arranged alternatively along the stems and form branchlets. The branchlets have opposite leaves which are sensitive to the touch. The flowers are yellow and occur in clusters that are ball-shaped and on stalks up to 20 cm long. Fruit are up to 28 mm long and 10 mm wide, and contain up to 8 brown seeds up to 5 mm long and 3.5 mm wide. Terrestrial forms of the plant generally have smaller leaves and flowers with no spongy tissue present on the stems.
Water mimosa is a water plant that usually lives on the surface of freshwater but can also grow in soil. Plants grow from a thick tap root, sending out stems that can reach 1.5 m long. Older stems growing in water develop a spongy covering which helps them float.
Plants that live on land generally have smaller leaves and flowers with no spongy tissue on the stems.
Where is it found?
Water mimosa has not been recorded in New South Wales, but has been found growing in in Queensland and the Northern Territory.
It is native to Mexico and north and south America. It is commonly grown throughout Asia as a vegetable and was brought into Australia for this purpose.
What type of environment does it grow in?
Water mimosa grows on the banks or edges of water bodies, where it spreads out over the water surface. It prefers shallow water (less than 1 m deep), full sun and hot conditions. It is found in:
- lakes
- farm dams
- ponds
- swamps.
It will also grow in slow moving water ways.
Maps and records
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Recorded presence of Water mimosa during property inspections (Map: Biosecurity Information System - Weeds, 2017-2026)
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?
By seeds
The pods produce viable seeds in Australia which can be spread by flowing water.
By plant parts
New plants can grow from stems. Broken stems are moved by flowing water especially floods.
Water mimosa has been spread deliberately by people planting stem fragments as a vegetable crop.
References
Biosecurity Queensland (2016) Water mimosa (Neptunia oleracea or Neptunia plena) Fact sheet, www.daf.qld.gov.au
Identic Pty. Ltd. & Lucid. (2016) Weeds of Australia Fact Sheet:Neptunia oleracea Lour. and Neptunia plena (L.) Available from: Benth. https://keyserver.lucidcentral.org/weeds/data/media/Html/neptunia_oleracea_and_neptunia_plena.htm
Northern Territory Government (n.d.) Weed List - water mimosa https://nt.gov.au/environment/weeds/weeds-in-the-nt/A-Z-list-of-weeds-in-the-NT/water-mimosa
Technigro Australia Pty Ltd (2011), Weed Watch Water mimosa (Neptunia oleracea)
More information
Control
It is important to remove all parts of the plant because it can easily regrow from stem fragments.
Physical removal
This is a common way to get rid of small areas of water mimosa. All parts of the plant need to be removed from the soil and water body to stop the plant re-growing and spreading. This will need to be done regularly until the plants stop re-growing.
Chemical control
Larger infestations can be controlled with herbicides. Herbicides must be registered 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
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 31/03/2030
Glyphosate 360 g/L
(Only products registered for aquatic use)
Rate: 200 mL per 10 L of water
Comments: Spot spray.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate
PERMIT 9907 Expires 31/03/2030
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: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate
Biosecurity duty
The content provided here is for information purposes only and is taken from the NSW 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. |
| North Coast |
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. This Regional Recommended Measure also applies to Neptunia plena |
| *To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here |
For technical advice and assistance with identification please contact your local council weeds officer.
Reviewed 2025
