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Cha-om (Senegalia pennata)

Cha-om is an invasive prickly shrub that can form dense thickets and outcompete native plants. In Australia, it has been found in food gardens on the North Coast and in disturbed areas in Queensland, often near rainforests.

Key facts

Type: Weed, shrub.

Native to: Myanmar, Indonesia, southern China and India.

Established in: QLD, NSW, NT.

Other names: khang, stinky leaf, Petai duri, Rau thoi.

Identification

  • It is a prickly shrub up to 5 m tall and can climb over nearby plants or structures.
  • Its fern-like leaves have 17–28 primary leaflets, each 3–10 cm long, divided into many pairs of small secondary leaflets.
  • The green secondary leaflets are oblong, 4–6 mm long and 0.5–1 mm wide, and the leaves smell foul when crushed.
  • Straight or backward-curving prickles, up to 10 mm long, are scattered along the stems.
  • White, cream or pale yellow pompom-like flower heads grow at stem ends; flattened, hairless pods ripen from green to brown and contain up to 8 seeds.
  • Look-alike: Leucaena (Leucaena leucocephala) lacks prickles and does not smell pungent when crushed; it also has larger flower heads, about 2 cm in diameter.
  • Look-alike: Common sensitive plant (Mimosa pudica) is a ground cover with pink flowers and leaves that close when touched, while poinciana (Delonix regia) grows up to 10 m, has red flowers and has seed pods up to 60 cm long.

Where it grows

In Australia, Cha-om has been found in food gardens on the North Coast and in disturbed sites in Queensland, often near rainforests, in tropical and subtropical climates.

Why it matters

  • Dense prickly thickets can limit the movement of people and animals, and the spines can cause injuries.
  • It outcompetes native plants and competes with pastures, reducing productivity.
  • By shading out ground covers, it can increase the risk of erosion.
  • It can climb over and damage fences and other structures.

How it spreads

  • Plants can produce seeds within a year; cattle eat the pods and spread seeds in their dung.
  • Seeds can also be spread by moving water.
  • Cha-om reproduces from stem fragments and where branches touch the ground, and stem fragments can spread in moving water.

Control options

  • Wear personal protective equipment, including gloves, to protect against the spines.
  • Individual smaller plants can be dug out by hand.
  • For cut-stump treatment, cut the plant and apply an herbicide to the remaining stump within 15 seconds; the listed option is Vigilant II gel containing picloram and aminopyralid, used according to its label and any permit conditions.
  • Contact your local council weeds officer for identification and control advice; in the North Coast region, notify the local control authority if the plant is found.

Hygiene and washdown

  • Pods can be eaten by cattle and seeds spread in their dung; seeds and stem fragments can also be spread by moving water.
  • 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: Prohibited matter. Report it to Biosecurity Queensland on 13 25 23 within 24 hours and do not move or deal with it. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Regional priority in 1 of 11 regions. Regional priority weed in North Coast. 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: Check NT list. There is no NT weed profile for it. Check the NT declared weeds list for its current status.
  • 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
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources