Water mimosa

Alert

Have you seen Water mimosa?

Be on the lookout for Water mimosa and report it to Biosecurity Queensland. Early detection and reporting are the key elements in controlling Water mimosa.

Call us on 13 25 23.

The term ‘water mimosa’ refers to the species Neptunia oleracea and Neptunia plena. Both are native to Mexico, Central America and northern parts of South America. N. plena also grows in tropical Asia, where it is farmed as a water vegetable.

Water mimosa is an aquatic, nitrogen-fixing legume that releases nitrogen into water bodies. This can lead to increased algal blooms and encourage growth of other weeds such as water hyacinth, water lettuce and salvinia. Excess nitrogen also affects water quality and increases water-treatment costs.

Water mimosa can grow on damp soil or as thick mats on water. It is found in scattered sites across Queensland.

Water mimosa is a restricted invasive plant under the Biosecurity Act 2014.

Scientific name

Neptunia oleracea, N. plena

Description

  • Floating perennial weed that attaches to bank at water's edge and sends down taproot.
  • Stems to 1.5m long, grow out over water and form spongy, fibrous covering between nodes.
  • Leaves have leaflets, 8-20 pairs per pinna. Leaflets are very sensitive to touch and close quickly.
  • Flowers are yellow, ball-shaped, 30-50 per spike and each flower is 7-16mm long, 0.5-1mm broad.
  • Seeds are oval and brown, 4-8 per legume. Each seed is 4-5.1mm long, 2.7-3.5mm broad.
  • On land, has smaller leaves and flowers, no spongy floating tissue.

Habitat

  • Grows on land in damp soil or on water as thick floating mats.
  • Commonly found in and around freshwater pools, swamps and canals.

Distribution in Queensland

  • Found in South East Queensland.

Life cycle

  • Grows from seeds and stem sections that break free from parent plant.
  • Flowering begins in early summer.

Affected animals

Native fish; people

Impacts

Environmental

  • Restricts water flow in creeks, channels and drains.
  • Increases water loss through evapotranspiration.
  • Reduces water quality by preventing light penetration and reducing oxygenation of water.
  • Creates favourable habitat for mosquitoes.
  • Reduces fish activity.
  • Kills native, submerged water plants and fish.
  • Replaces native wetland plants.

Social

  • Impedes recreational water sports and boating access.

How it is spread

  • Has been subject to sale and distribution through Asian communities and gardeners.
  • Floating rafts of dense inter-woven stems can be dislodged by water movement (especially during floods) and re-establish further downstream.

Control

Mechanical control

  • Remove all plant matter from infested water body and pull plants out of surrounding banks, making sure to remove attached root system.
  • Dispose of plant parts in an appropriate waste facility or rubbish bin.

Herbicide control

  • No herbicides are registered for control.

Biological control

  • No known biological control agents.

Legal requirements

  • Water mimosa is a restricted invasive plant under the Biosecurity Act 2014.
  • All sightings must be reported to Biosecurity Queensland within 24 hours of the sighting.
  • It must not be given away, sold, or released into the environment without a permit.
  • The Act requires everyone to take all reasonable and practical steps to minimise the risks associated with invasive plants and animals under their control. This is called a general biosecurity obligation (GBO).
  • At a local level, each local government must have a biosecurity plan that covers invasive plants and animals in its area. This plan may include actions to be taken on certain species. Some of these actions may be required under local laws. Contact your local government for more information.

More information