Water mimosa - plena (Neptunia plena)
Water mimosa (plena) is a perennial aquatic plant with fern like leaves and yellow flowers. It outcompetes native plants and reduces food and habitat for fish and other aquatic animals.
Profile
How does this weed affect you?
Water mimosa (plena) grows on the edges of waterways and can form floating rafts. It can:
- outcompete native aquatic plants
- reduce food and habitat for fish and other aquatic animals
- reduce water quality by reducing light and oxygen levels and increasing nitrogen levels, which could lead to an increase in algal blooms
- increase water loss in dams through increased evapotranspiration
- limit water flows in creeks, channels and drains, increasing the risk of floods
- create more suitable habitat for mosquitoes
- limit access to waterways for fishing, boating and other recreational activities.
What does it look like?
Water mimosa (plena) is a perennial upright herb that can grow in the water and on land.
Leaves:
Leaves are divided into 2–5 pairs of primary leaflets, which are further divided into 9–38 pairs of secondary leaflets. The leaflets are:
- olive green with minute dots
- oblong
- 4–18 mm long and 2.0–3.5 mm wide
- hairless or with small hairs on the margins
- in opposite pairs
- are sensitive and close together in pairs when touched.
Leaves are smaller on plants growing on land.
Flowers are:
- yellow
- in a ball shaped cluster (1–2 cm wide), and made up of up to 60 flowers
- on stalks 3–17 cm long.
Fruit are:
- flat oblong pods that contain 8–20 seeds
- 1.5–5.5 cm long and 0.7 –1.1 cm wide
- leathery.
Seeds are:
- brown
- egg shaped
- about 4 mm long and 1 mm wide.
Stems:
- are up to 2 m long
- are branched
- are usually upright
- form a spongy-fibrous coating when growing in the water
- are reddish on plants that grow on the land.
Roots:
- Free floating plants produce roots at the nodes along the stems.
- Plants growing on land have a thick taproot that becomes woody with age.
Similar looking plants
Water mimosa (plena) looks similar to:
- Water mimosa- oleracea (Neptunia oleracea), which does not have upright stems and the stems are not usually branched. It has less seeds per pod (4-8) and the seeds are slightly larger.
- Common sensitive plant (Mimosa pudica), which has pink flowers. It also has hairy leaves, stems and pods.
Where is it found?
Water mimosa (plena) has not been found in NSW. It has been found in Queensland in scattered locations from Brisbane to North of Cairns. In the Northern Territory it has been found in Darwin and the northeast.
All Australian plants have been, or are in the process of being eradicated.
Water mimosa (plena) grows in coastal regions of southern North America, Central America, northern South America and tropical parts of Asia. It was introduced to northern Australia as a vegetable.
What type of environment does it grow in?
Water mimosa (plena) plants mostly grow in tropical and subtropical climates. Plants grow best in full sun in hot humid conditions. They do not tolerant shade, dry conditions, brackish water or saline soils. Water mimosa (plena) can root in the banks of waterways or form floating rafts of plants. They prefer slow-moving fresh water 30–80 cm deep. Canals, dams, ponds, lakes and swamps are ideal areas for it to grow in.
Maps and records
-
Recorded presence of Water mimosa - plena 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
Plants produce viable seeds, which are spread by water. Seeds could also be spread in mud attached to vehicles and machinery.
By plant parts
New plants can grow from stem fragments. Broken stems spread in flowing water especially during floods. Water mimosa (plena) has been deliberately spread by people planting stem fragments as a vegetable crop.
References
Csurhes, S. (2016). Invasive species risk assessment: Water mimosa (Neptunia oleracea or Neptunia plena. Biosecurity Queensland.
Identic Pty. Ltd. & Lucid. (2016) Weeds of Australia Fact Sheet: Neptunia oleracea Lour. and Neptunia plena (L.) Retrieved 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
Department of Primary Industries, The State of Queensland. (2025). Water mimosa fact sheet Neptunia oleracea and Neptunia plena. Retrieved 9 June 2026 from: https://www.publications.qld.gov.au/ckan-publications-attachments-prod/resources/de4bbf5b-e4e0-4f53-8e46-87c9c2d7d0f0/water-mimosa.pdf?ETag=4bfa23e0e52af59f7b10289760e0eaee
Windler, D. R. (1966). A revision of the genus Neptunia (Leguminosae). Australian Journal of Botany, 14(3), 379-420.
Control
Physical removal
For small infestations, dig out the roots if in the soil and remove all parts of the plant. When growing in the water remove all of the plant. Check the site regularly for any regrowth.
Herbicide control
Larger infestations can be controlled with herbicides. Use herbicides registered for aquatic use.
Herbicide options
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 |
Reviewed 2026
