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Mysore thorn (Biancaea decapetala)

Mysore thorn forms dense, prickly thickets that restrict access for people and animals and can injure them. It invades pastures and native vegetation, and can damage infrastructure and increase flood damage.

Key facts

Type: Weed, shrub.

Native to: Japan, China, India and Malaysia.

Established in: QLD, NSW.

Other names: wait-a-while, thorny poinciana.

Best time to act: Treat plants while actively growing and before flowering, which occurs from winter to spring.

Identification

  • It is a prickly, perennial evergreen shrub up to 4 m tall, or a climber that can reach 20 m over supporting vegetation or buildings.
  • Its fern-like leaves are 7–40 cm long and divided into many small, hairy, oblong leaflets.
  • Yellow or pale-yellow flowers, occasionally white, have five petals and grow in spike-like clusters at branch tips; flowering occurs from winter to spring.
  • Its hairy, flat seedpods are 6–10 cm long, turn brown when mature and have a small pointed beak; they usually occur from August to December.
  • Stems have curved or straight prickles, and young stems are smooth and creamy-green.
  • Look-alike: Dwarf poinciana (Caesalpinia gilliesii) has no prickles and has long, bright-red, thread-like stamens; honey locust (Gleditsia triacanthos) is a tree with long straight spines and small, inconspicuous flowers.
  • Look-alike: Parkinsonia (Parkinsonia aculeata) also has small curved prickles, but its flowers have four yellow petals and one orange or orange-spotted petal.

Where it grows

In NSW it occurs in the North Coast, Hunter, Greater Sydney and South East regions, often in disturbed areas, pastures, creek banks, native grasslands and along bushland and forest edges.

Why it matters

  • Dense thickets restrict access for people and animals, including access to water, and the prickles can cause injuries.
  • It invades pastures, reducing productivity, and outcompetes and smothers native vegetation.
  • It reduces shelter and food for native animals and can harbour feral animals.
  • It can restrict water flows and flood-debris movement, increasing flood damage, and can damage sheds and fences.

How it spreads

  • Seeds can remain viable in soil for up to 10 years.
  • Rodents, birds and cattle can spread seeds after feeding on the pods.
  • Seeds can also spread in moving water or contaminated soil and mud on vehicles or machinery.

Control options

  • Wear protective clothing to protect skin and eyes from the prickles.
  • Dig up small plants and remove all roots; larger plants or infestations can be removed by machinery if this will not damage native vegetation, removing as much root material as possible.
  • For dense infestations, check for regrowth and follow up; use registered herbicides according to the label, including spot spraying actively growing plants or cut-stump treatment.
  • Control plants before flowering to minimise seed production, and monitor treated areas for seedlings and regrowth.

Hygiene and washdown

  • Clean vehicles and machinery that have been in infested areas before leaving the site.
  • Keep cattle from infested areas in a holding paddock before moving them elsewhere, allow time for seeds to pass through their gut, and inspect the paddock for seedlings.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Regional priority in 4 of 11 regions. Regional priority weed in Greater Sydney, Hunter, North Coast, South East. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development

Sources