Native to tropical Africa and Asia, calotrope is a spreading shrub or small tree with white-and-purple flowers. Calotrope was introduced into Australia as an ornamental shrub.
Calotrope can readily become established in areas disturbed by vegetation clearing, road-making or heavy grazing.
Calotrope is not a prohibited or restricted invasive plant under the Biosecurity Act 2014.
Rubber bush, kapok tree, king's crown, cabbage tree, rubber tree
- Spreading shrub or small tree up to 4m tall.
- Plant oozes milky sap when any part is cut or broken.
- Stems are smooth, pale greyish-green.
- Mature stems have beige corrugated bark, cork-like appearance and texture.
- Leaves are grey-green, large, 10-20cm long, 4-10cm wide, with short pointed tip and heart-shaped base, attached in opposite pairs directly to stem.
- Flowers are waxy, 5-petalled, white with purple on inside of tips, have central purplish crown, grow in groups in forks of uppermost leaves with up to 15 flowers per group.
- Fruit is large, green, inflated, rounded at base and pointed at tip, similar to mango, 8-12cm long, almost as wide.
- Seeds have tufts of long, silky hairs at one end.
- Invades roadsides, watercourses, old cultivated land and heavily grazed areas.
Distribution in Queensland
- Naturalised in semi-arid north Queensland, particularly in Gulf of Carpentaria.
- Extensive infestations on some Gulf islands, particularly on sandy foreshore areas.
- Can regrow from root system when above-ground plant removed.
- Seed longevity appears to be relatively short (around 12-24 months if sufficient rainfall occurs to promote germination).
- Humans; cattle
- Dense thickets on alluvial flats or along rivers reduce grazing and water access.
- Cattle subjected to stress (mustering, etc.) may die from poisoning.
How it is spread
- Fruit bursts, releasing numerous seeds that are carried long distances by wind.
- Spreads rapidly from base of plants.
- Roots are large and spongy; new plants quickly grow from large taproot if plant is cut off at ground level. Machinery capable of cutting plants off 10-20cm below ground (e.g. blade ploughs or cutter bars) can cause high kill rates.
- With mechanical disturbance, large-scale seedling regrowth should be expected afterwards.
- Calotrope appears to tolerate fire and, although above-ground portion is often killed, plants will vigorously reshoot from base.
Basal bark treatment
- For stems up to 10cm diameter, carefully spray around base of plant to about 30cm above ground level. Thoroughly wet stem to point of run-off, all the way around, to ensure that spray mix soaks through corky bark. All stems on multi-stemmed plants must be treated.
Cut stump treatment
- Plants can be cut-stumped up to and in excess of basal bark sizes. Cut stems off horizontally as close to ground as possible and immediately spray cut surface and remaining bark liberally with spray mixture.
- Foliar spraying of seedlings and young plants to 2m tall may be undertaken with registered products according to label recommendations. Add wetting agent and thoroughly spray whole plant to point of run-off.
See the Calotrope fact sheet (PDF, 1.6MB) for herbicide control and application rates.
- No known biological control agents .
- Calotrope is not a prohibited or restricted invasive plant under the Biosecurity Act 2014. However, by law, everyone has a general biosecurity obligation (GBO) to take reasonable and practical steps to minimise the risks associated with invasive plants and animals under their control.
- Local governments must have a biosecurity plan that covers invasive plants and animals in their 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.
- Last updated
- 01 July 2016