Quick Facts

Quick facts

• Calotrope (Calotropis procera) is an upright, branched shrub or small tree with milky sap usually growing 1 to 4 m tall.
• It forms dense thickets on alluvial floodplains and over-grazed pastures in the drier regions of northern Australia.
• Calotrope hinders pastoralism by reducing the productivity of rangeland pastures and making mustering more difficult.
• It also competes with native grasses and can transform the appearance of grassland plant communities.
• Calotrope is difficult to eradicate once established; however, several effective herbicides are in the process of being registered.

What Does It Look Like?

What is it?

Calotrope (Calotropis procera) is an upright branched shrub or small tree usually growing 1 to 4 m tall. The stems and leaves have a waxy appearance and contain a milky sap. Branching occurs from the base of the plant upwards. Younger stems are greyish-green in colour, smooth in texture, and have a covering of small whitish hairs. Mature stems have a deeply fissured, cork-like, bark that is light brown in colour. The large, relatively thick, leaves (5 to 30 cm long and 4 to 15 cm wide) are also greyish-green in colour and have smooth margins. They are oppositely arranged and have stem-clasping bases or are borne on very short stalks (3 to 4 mm long). These leaves are rounded or oval shaped with shortly-pointed tips. Their upper surfaces are mostly hairless, while their undersides may be densely covered in tiny white hairs or have a tuft of stiff hairs at the base of the midrib.

The flowers are borne in clusters, each containing 3 to 15 flowers, in the forks of the uppermost leaves. The main stalk of these flower clusters is 20 to 55 mm long and each flower has is borne on a stalk about 15 to 25 mm long. These trumpet-shaped flowers (15 to 25 mm across) have five spreading petals (7 to 10 mm long and 6 to10 mm wide) that are white or pinkish in colour, with much darker purple or purplish-brown tips, and a crown-shaped centre that is also purplish in colour. The fruit pod is large (6 to 12 cm long and 3 to 7 cm wide), greyish-green in colour and rounded to somewhat egg-shaped. These fruit have thick and spongy skins which split open at maturity. Each fruit contains numerous brown, flattened seeds (about 6 mm long and 4 mm wide) that are topped with a tuft of long, white, silky hairs (35 to 50 mm long) (Navie & Adkins 2007).

For further information and assistance with identification of Calotrope contact the herbarium in your state or territory.

Flower colour

Multi-colour

Growth form (weed type/habit)

Shrub

Where it currently grows? Preferred habitat

Calotrope is mostly found in semi-arid and arid inland areas, as well as in drier habitats in tropical and sub-tropical regions. A weed of disturbed sites, roadsides, waste areas, inland watercourses, coastal sand dunes, grasslands, open woodlands and pastures (Navie & Adkins 2007). It thrives on poor soils, particularly where overgrazing has removed competition from native grasses (Smith 2002).

Are there similar species?

Calotrope is very similar to Giant Calotrope (Calotropis gigantea) and they are often confused. However, Giant Calotrope grows into a large shrub or small tree, often reaching more than 4.5 m tall. Giant Calotrope flowers also have relatively long and narrow petals that are uniformly pink or mauve in colour, while Calotrope flowers have relatively short and broad whitish petals with much darker purple tips (Navie & Adkins 2007).

Why Is It A Weed?

What are its impacts?

Calotrope was included in the list of 71 species that were nominated by state and territory governments for assessment as Weeds of National Significance (WONS). Following an assessment process, Calotrope was not included as one of the 20 WONS. However, it remains a weed of potential national signficance.

The milky sap of this species is toxic to humans and sometimes also to livestock. Calotrope hinders pastoralism by reducing the productivity of rangeland pastures and making mustering more difficult (Navie & Adkins 2007). It forms dense thickets on alluvial floodplains and then spreads into adjacent over-grazed pastures (Parsons & Cuthbertson 2001). It thrives on poor soils, particularly where overgrazing has removed competition from native grasses, and forms dense thickets which compete with native plant species and transform the appearance of grassland plant communities (Smith 2002).

Calotrope is currently listed as a priority environmental weed in three Natural Resource Management Regions and is being actively managed by community groups in the Northern Territory (Navie & Adkins 2007).

How does it spread?

Calotrope reproduces mainly by seed, though local increase in the size and density of populations also occurs via suckering from the roots. The seeds can be spread long distances by wind and water, and may also be dispersed in mud sticking to animals and vehicles (Parsons & Cuthbertson 2001).

What is its history in Australia?

Calotrope is thought to have been introduced into Australia during one of the Queensland gold rushes in the late 1800s or early 1900s. It is not known exactly how it was introduced, but it may have been deliberately introduced as an ornamental or accidentally introduced in the packing of camel saddles. Calotrope was first recorded as naturalised in semi-arid northern Queensland in 1935, but was probably present for some time prior to this (Parsons & Cuthbertson 2001).

How To Manage It?

Best practice management

Calotrope roots are large and spongy and readily produce suckers. Once established, it is difficult to eradicate, as these deep roots survive almost any treatment. This makes any form of mechanical control, including fire, relatively ineffective. However, it is susceptible to regular cultivation (Crothers & Newbould 1998).

Several herbicides have been found to be effective when applied as a foliar spray, or by using the cut stump and basal bark methods. These herbicides are currently in the process of being registered (Land Protection 2006). Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au .

Check with your local council or state/territory government weed management agency about its requirements for Calotrope control.

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

In the monsoonal regions of tropical Australia, seeds germinate with the onset of the wet season (usually between October and December). Calotrope can grow quite quickly during the wet season and it is thought that plants begin to flower when they are about 2 years old. Flowering occurs mainly during winter, with the first flowers opening in July (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

NSW, NT, QLD, SA, WA

What areas within states and territories is it found?

This species is widespread in the drier parts of northern and central Australia. It is mostly commonly found in northern Queensland, north-western Western Australia and the northern parts of the Northern Territory. It is also present in other parts of the Northern Territory and has been recorded in South Australia and New South Wales (Navie & Adkins 2007).

Where does it originate?

Calotrope is native to northern Africa, the Arabian Peninsula, the Middle East and parts of southern Asia such as Afghanistan, Pakistan, Nepal, India, Myanmar, Thailand and Vietnam (GRIN 2007).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NT, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Calotropis procera

Other scientific names (synonyms)?

• Asclepias procera Aiton
• Asclepias gigantea L. (misapplied by Jacquin, N.J. von 1768, Observationum Botanicarum. 3: t. 69.)

Does it have other known common name(s)?

Rubber Bush, Calotropis, Rubber Plant, Cabbage Tree, Kapok Tree, Giant Milkweed, Indian Milkweed, King Edward's Crown, Small Crown Flower