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Native to South America, hymenachne is a robust, rhizomatous, perennial grass. Originally introduced to Australia to provide ponded pasture for cattle, it is now found from far north Queensland to Casino in New South Wales, and in the top end of the Northern Territory.

Hymenachne has become an unwanted pest of streambanks, shallow wetlands and irrigation ditches, primarily in the coastal Wet Tropics of northern Queensland. In some areas it has invaded low-lying sugarcane fields, fish habitats and natural wetlands with high conservation value. Hymenachne damages wildlife habitats and irrigation channels, and degrades recreational water quality.

Hymenachne is a restricted invasive plant under the Biosecurity Act 2014.

Scientific name

Hymenachne amplexicaulis

Other names

  • Olive hymenachne

Similar species

  • Native hymenachne (H. acutigluma)


  • Robust, rhizomatous, perennial grass, up to 2.5m tall.
  • Stems are erect and pithy.
  • Leaf blades are 10-45cm long, up to 3cm wide.
  • Flower heads are spike-like, cylindrical, 20-40cm long.


  • Prefers streambanks, shallow wetlands and irrigation ditches.


  • Found from Cape York to New South Wales border.

Life cycle

  • Flowering occurs April-June.
  • Seeds set from late autumn to early spring.
  • One flower stalk can produce more than 4000 seeds.
  • Seed viability is 8-24% after 8 years.

Affected animals

  • Fish
  • Humans
  • Native Animals



  • Affects drains, lagoons, wetlands, creeks and rivers.
  • Increases flooding by reducing flow capacity of drainage networks.
  • Interferes with wildlife habitats.


  • Interferes with irrigation and infrastructure.


  • Degrades water quality for recreational purposes.

How it is spread

  • Seeds spread by water movement and migratory aquatic birds.


Physical/mechanical control

  • Mechanical or physical removal will not completely eradicate hymenachne because of the plant's ability to reproduce vegetatively from very small pieces.
  • Heavy earth-moving machinery can be effective.
  • Fire is a tool for the dry season. When integrated with other control methods, fire can improve overall results and reduce cost.

Herbicide control

  • No herbicides are currently registered. However, off-label minor use permits are available.
  • Spraying an entire heavy infestation can cause hymenachne to sink and result in biological hazards from rotting vegetation. Large masses of decomposing hymenachne may use all oxygen in water, leading to fish kills. Avoid this problem by spraying strips of weed.

See the Hymenachne fact sheet (PDF, 1.1MB) for herbicide control and application rates.

Biological control

  • No biological control agents released in Australia.
  • Should a biological program commence, agents sought would need to be specific for olive hymenachne to ensure no impacts on native species (H. acutigluma) or other desirable grasses.

Legal requirements

  • Hymenachne is a restricted invasive plant under the Biosecurity Act 2014.
  • 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.

Further information