Narrowleaf cotton bush balloon pods © Richard Fuller

​​Narrowleaf cottonbush​

​​Gomphocarpus fruticosus​

Quick facts

Status
Declared Pest (C3)
Life Cycle
Perennial
Growth Form
Shrub
Origin
Southern and eastern Africa
Flowers
White/cream
Dispersal
Wind, water
Toxicity
Sap poisonous to humans and livestock

Names

Other Common Names: Swan Plant, Swanplant, Milk Weed, Milkweed, Cape Cotton, Duck Bush, Swan Bush, Wild Cotton.

Synonyms: ​​Asclepias fruticosa.

Form and function

​​Native to southern and eastern Africa (from South Africa to Ethiopia, Somalia and Eritrea) and the Arabian Peninsula (Oman, Yemen and the southern parts of Saudi Arabia).​ The plant reproduces through both seed and vegetative growth via root suckers. It spreads mainly by fluffy, wind-dispersed seeds that can also float on water, while mud attached to animals, machinery and vehicles can further aid dispersal. Plants typically reach maturity within two years and grow to 0.5 to 2 m tall. Seeds can persist in the soil for more than five years. Intense fire may kill mature plants and destroy seeds stored in the soil.

Flowers

  • Flowers can grow up to 20 mm long and 13 mm wide.
  • Flowers arranged in loose, drooping clusters in the forks of upper leaves.
  • Each cluster contains about 3 to 10 flowers.
  • Individual flowers held on slender stalks (up to 10 mm long) that radiate from a single point.
  • Five narrow sepals present.
  • Five stamens present.
  • A distinctive crownlike structure formed by five pouch shaped projections in the centre.

Narrowleaf cottonbush flower © Steve Dew

Leaves

  • Arranged opposite along the stems.
  • Narrow to very elongated in shape (4 to 12.5 cm long and 5 to 15 mm wide).
  • Tapering to a point at both ends.
  • Held on short stalks 3 to 10 mm long.
  • Upper surface shiny and pale green.
  • Lower surface paler and duller.

Narrowleaf cottonbush leaf close up © Nick Lambert

Fruits

  • Balloon‑like and bladdery in appearance.
  • Light green.
  • 4 to 7 cm long and 1.5 to 3.5 cm wide.
  • Slightly curved and narrowing to a short beak at the tip.
  • Surface covered with soft spines up to about 10 mm long.
  • Fruit splits open at maturity.
  • Each fruit contains numerous seeds (6 mm long and 3 mm wide).
  • Seeds brown to black, flattened, and topped with a silky white hair tuft about 30 mm long.

Narrowleaf cottonbush flower © Richard Fuller

Roots

  • Shallow root system.

Habitat

Prefers warm temperature where adequate soil moisture is available. It can establish in wide range of environment, including roadsides, disturbed areas, waste areas, waterway, pastures, open woodland and fallows. It can also tolerate warm temperate, sub-tropical, tropical and occasionally semi-arid regions. 

May be confused with...

Similar non-native species: ​​Similar to Balloon Cotton Bush (Gomphocarpus physocarpus) which is rarely found in Western Australia but common in southern Queensland. While the narrowleaf cottonbush has egg-shaped fruit with gradually taper toward the end, the ballon cotton bush has almost round fruit shape, often with a sunken tip.​ 

How does it spread?

This plant reproduces both by wind-dispersed seeds and vegetatively through root suckers located near the soil surface. The fluffy seeds can be carried long distances by wind and also float on water. Additional spread occurs when seeds or plant material are transported in mud attached to animals, machinery, and vehicles.

Why is it a weed?

  • Capable of forming dense thickets that exclude other vegetation.
  • Whole plant is poisonous to human and livestock.

History

Originally introduced as an ornamental garden plant.

How to control

Arum Lily

Physical

Arum Lily

Chemical

Arum Lily

Managerial

Arum Lily

Biological

Physical

​​Hand pulling: Manual removal is effective for small infestations but must be conducted before flowering to prevent dispersal of seeds. Make sure to remove all the crown and roots as possible to minimise root suckering. To avoid the contact with poisonous sup, wear rubber gloves and overalls and wash hands after hand pulling. Plants that have been removed will dry out quickly and should be burnt, deep buried or discard of carefully.

​

Slashing: During winter, slashing can be effective to suppress further infestation, as long as conducting repeatedly for seedlings and regrowths or apply herbicides before flowering.​ 

Chemical

For large infestations, apply 1.5% w/v glyphosate (450g/L) in water using a foliar application method (i.e. spraying foliage with a backpack sprayer, knapsack sprayer or tank and pump spray), ensuring full foliage coverage. Alternatively for larger plants, cut stump close to the ground and paint immediately using a 50% glyphosate solution while the plant is actively growing.​ Due to its long seedbank persistence, herbicides need to be repeatedly applied for several years with periodical monitoring and slashing if needed. 

Managerial

Revegetation where canopy cover is added will reduce habitat for cottonbush which prefers and open canopy.

Biological

Cottonbush has a range of natural enemies in Western Australia that occasionally have a significant impact on growth.  It is fed on by the larvae of the wanderer butterfly Danaus plexippus, and its flowers are also visited by the native lesser wanderer butterfly Danaus petilia. A hemipteran bug Arocatus rusticus also feeds on cottonbush seeds and also a sap sucking aphid Aphis nerii.  None of these natural enemies were deliberate biocontrol agent release, but native and non-native insects that have found cottonbush a suitable host. 

Further
reading

Minor use permit
external link Permit PER96570 for glyphosate

Weed Distribution Map

LSID number: [4092442] | full LSID: [https:/id.biodiversity.org.au/node/apni/4092442] | field_lsid: [] | taxon: [​​Gomphocarpus fruticosus​]

ALA Reference

References

  • Department of Primary Industries and Regional Development. (n.d.). Narrow leaf cotton bush: declared pest.
  • WeedsAustralia. (2024). Narrow Leaf Cotton Bush, Narrow-Leaved Cotton Bush, Narrowleaf Cottonbush, Swan Plant, Swanplant, Milk Weed, Milkweed, Cape Cotton, Duck Bush, Swan Bush, Wild Cotton
  • Western Australian Herbarium (2019) Gomphocarpus fruticosus (L.) W.T.Aiton. Florabase—the Western Australian flora. Department of Biodiversity, Conservation and Attractions
  • Campos, M., Batchelor, K.L., Bell, K.L., Davy, M., Christensen, M., Didham, R.K. & Webber, B.L. (2023) Cottonbush invasion in Western Australia: ecology and social perspectives. In: Proceedings of the 22nd Australasian Weeds Conference, Adelaide, South Australia. Council of Australasian Weed Societies, Adelaide, Australia
  • Atlas of Living Australia. (n.d.) Gomphocarpus fruticosus (L.) W.T.Aiton.

Life Cycle

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Notes
Germination
Active growth
Flowering
Fruiting
Regularly or most commonly
Occasionally, given suitable conditions

Management

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Notes
Physical
Glyphosate
Optimal
Potentially, but conditionally dependent
Last updated: September 2026