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.

Profile

How does this weed affect you?

Water mimosa impacts waterways when it smothers native vegetation and reduces oxygen levels in the water. Dense rafts of water mimosa also restrict water flow leading to increased flood risks and restricted recreational use.

Where is it found?

Water mimosa is found in Mexico, Africa, parts of Asia where it is cultivated as a vegetable, Central America and parts of South America. Water mimosa has not been recorded in New South Wales, but has been found growing in several locations in Queensland and the Northern Territory. 

How does it spread?

Water mimosa grows out over the surface of waterways in rafts. Plant fragments can break off these rafts and start new infestations. Plants also produce seed. The deliberate planting of stem fragments to be grown for human consumption is one of the main pathways of spread of this plant.

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.  

Habitat

Plants grow best in still to slow moving waterways up to 1 metre deep, and prefer full sun and hot conditions.

Acknowledgements

Author: Charlie Mifsud

Technical review: Rod Ensbey

References

Biosecurity Queensland (2016) Water mimosa (Neptunia oleracea or Neptunia plena) Fact sheet, www.daf.qld.gov.au

Northern Territory Government (n.d.) Weed List - water mimosa 

Technigro Australia Pty Ltd (2011), Weed Watch Water mimosa (Neptunia oleracea)

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Control

Herbicide options

Contact your local council weeds officer for control advice for Water mimosa (Neptunia oleracea).

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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.
North Coast 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.
This Regional Recommended Measure also applies to Neptunia plena
*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfill the general biosecurity duty for this weed click here

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Reviewed 2017