Calotrope (Calotropis procera)

Assessment ID: 1189
Jurisdiction: North Territory
Methodology: Northern Territory Weed Risk Management System - terrestrial
Management area: Alice Springs Region

Notes:

Status: PUBLISHED
Last updated: 18/3/2025 4:05:56 pm AEST

Questions answered: 39 / 47

Weed Risk: 152.80 (High)
   Invasiveness (raw/adjusted): 6.00 / 4.998
   Impacts (raw/adjusted): 6.50 / 3.419
   Potential distribution (raw/adjusted): 17.00 / 8.942

Feasibility of Control: 157.28 (High)
   Control costs (raw/adjusted): 5.00 / 4.545
   Current distribution (raw/adjusted): 5.00 / 5.000
   Persistence (raw/adjusted): 9.00 / 6.921

Result: Protect priority sites

Invasiveness

A1. What is the ability of the plant to establish amongst intact native environments?
Answer: Medium

Comments: Most common in disturbed areas including roadsides, watercourses, river flats, coastal dunes, wastelands, cleared areas and overgrazed areas (Parsons & Cuthbertson 2001, Smith 2002). Seed germination is thought to require exposure to red light and is reportedly inhibited under a dense tree canopy (Parsons & Cuthbertson 2001). Seed germination not affected by light (Amritphale et al. 1984). In a survey of landholders and weed experts in the NT, 57% of respondents believed it does invade areas with good pasture cover (Grace 2006). Plant densities were similar between grazed and ungrazed plots (Bastin et al. 2003).

A2. What is the reproductive ability of the plant?

(a) Time to seeding
Answer: 2-3 years

Comments: Age at first flowering appears to be 2 years but this is not known with any certainty Parsons & Cuthbertson 2001).

(b) Annual production of viable seed /m2 or /plant
Answer: High

Comments: Reproduces by seeds which germinate between October and December in the NT. Produces large fruit, each containing numerous seeds (Parsons & Cuthbertson 2001). Hundreds to thousands of seed may be produced per plant each year (Francis 2009).

(c) Vegetative reproduction
Answer: Infrequent

Comments: Local stands increase in size by suckering (Smith 2002). Increase in size and density of colonies occurs as a result of suckering from roots and crowns (Parsons & Cuthbertson 2001).

A3. Do propagules of the plant have properties that allow them to be dispersed long-distance by natural means?

(a) Flying animals (birds, bats)
Answer: No

Comments:

(b) Other wild animals
Answer: Do not know

Comments:

(c) Water
Answer: Yes

Comments: Seeds are buoyant in water (Grace 2006). Seeds have tufts of long hair which may aid in long distance dispersal. Dispersal is principally by wind and water (Parsons & Cuthbertson 2001).

(d) Wind
Answer: Yes

Comments: Seeds have tufts of long hair which may aid in long distance dispersal. Dispersal is principally by wind and water (Parsons & Cuthbertson 2001).

A4. How likely is long-distance dispersal by human-assisted means?

(a) Deliberate spread by people
Answer: Unlikely

Comments:

(b) Accidentally by people and vehicles
Answer: Occasional

Comments: Seeds may be moved in mud sticking to machinery (Parsons & Cuthbertson 2001).

(c) Contaminated produce
Answer: Unlikely

Comments:

(d) Domestic/farm animals
Answer: Occasional

Comments: Seeds may be moved in mud sticking in the hooves of animals (Parsons & Cuthbertson 2001). Seeds are commonly observed germinating in cattle dung heaps in India (Kumar et al. 1997).

Impacts

B1. What is the plant's competitive potential?
Answer: Do not know

Comments: It forms dense thickets which compete with native species and transforms the appearance of savanna (Smith 2002). Little is known about the population dynamics and in particular the competitive ability of this species. In a survey of land holders, many suggested it shades out and out-competes pasture (Grace 2006). Successfully competes with desirable pasture species (Smith 2001). Can form dense thickets that interfere with stock management, particularly mustering (Grace 2006).

B2. What is the plant’s potential to modify the existing fire behaviour and alter the fire regime?
Answer: Some potential

Comments: Remains evergreen year round (No reference).

B3. What is the plant’s potential to restrict the physical movement of people, animals, vehicles, machinery and/or water?
Answer: Low

Comments: Forms dense thickets making mustering difficult (Smith 2002). Forms dense thickets that interfere with stock management (Grace 2006).

B4. What is the plant’s potential to negatively affect the health of animals and/or people?
Answer: Low

Comments: A recent survey of landholders and weed specialists across the Northern Territory, suggests that the plant is commonly browsed by cattle across its range and that there is little evidence that stock die or become sick as a result of browsing on C. procera in Australia (Grace 2006). Latex may cause irritation and blistering if it comes in contact with mucous membranes in humans (Parsons & Cuthbertson 2001). ‘C. procera contains a range of toxic compounds many of which are concentrated in the latex. Leaves can take up heavy metals (Pb, Co, Ni, Mn, Cr, Cd and Cu) present in the environment (Díaz & Massol-Deya 2003). Although ingesting large quantities of latex has killed goats and rats, it is important to note that ruminants are often more tolerant of ingested organic toxins better than non-ruminants such as rats, and that there is little latex in the leaves, the part most likely to be eaten by stock (Parsons & Cuthbertson 2001). One weed specialist commented that cattle can become sick after eating large quantities of leaves, which rarely happens (Grace 2006, M. Fuller [Territory Weed Management] 2006, pers. comm.).

B5. Does the plant potentially have negative effects on natural and cultural values?

(a) Reducing habitat quality for native animals?
Answer: Medium

Comments: Forms dense thickets which compete with native plant species and transform the appearance of landscapes (Smith 2002).

(b) Threatened species or communities
Answer: None identified

Comments:

(c) Sites of natural or cultural significance
Answer: None identified

Comments:

B6. Is the plant presumed to have negative effects on environmental health?

(a) Soil chemistry/stability
Answer: No

Comments:

(b) Water quality
Answer: No

Comments:

(c) Hydrology
Answer: No

Comments:

Potential distribution

C1b. What is the Climatch suitability score (which indicates the proportion of the NT environment that is suitable for the plant)?
Answer: 10

Comments: The CLIMATCH model used by the NT Weed Management Branch predicts that 100% of the NT is climatically suitable for Calotropis procera (see Figure 1) (NT Weed Management Branch 2007).

C2. How many broad habitat types in the NT will the plant potentially naturalise in (up to 5)?
Answer: Five or more

Comments: The broad vegetation types that Calotropis procera will potentially naturalise in are: - Tropical open forests/savanna woodlands - Tropical riparian areas - Mitchell grasslands - Arid and semi arid woodlands - Arid and semi-arid shrublands - Arid riparian The favoured vegetation types are tropical open forests/savanna woodlands and Mitchell grasslands (NT Weed Risk Management Committee 2007).

C3. What is the potential of the plant to occur throughout its favoured habitat in the NT (as identified in question 2)?
Answer: Some

Comments: Calotropis procera has the potential to occur through some of its favoured habitat (NT Weed Risk Management Committee 2007).

Control costs

A1. How detectable is the weed?

(a) Distinguishing features
Answer: Always distinct

Comments: Always distinct (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Rubber bush (Calotropis procera) is a shrub or small tree 3-5 m tall. Has a waxy appearance and milky sap. Stems are smooth, grey green. Leaves thick and waxy and heart shaped. Flower are white with purple blotches at tip. Pods are green bladder like, splitting to release white-plumed seeds (Smith 2002).

(b) Active growth period
Answer: <4 months

Comments: The active growth period in the Alice Springs region is <4 months (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). The active growth period in the Katherine region is 4-8 months. (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). The active growth period in the Darwin region is > 8 months. (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007).

(c) Height at maturity
Answer: >2 m

Comments: The height at maturity is >2 m (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Rubber bush (Calotropis procera) is a shrub or small tree 3-5 m tall (Smith 2002).

A2. What is the general accessibility of infestations at the optimum treatment time?
Answer: Medium

Comments: The general accessibility of infestations is medium (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Medium (Michelle Kassman, pers comm., Regional Weeds Officer – Barkly, NT Weeds Management Branch). Medium (most of work with 4WD quadbikes) (Chris Brown, pers comm., Regional Weeds Officer – Alice Springs, NT Weeds Management Branch).

A3. How expensive is control of the weed in the first year of targeted control, for an infestation that has reached maximum weed density?

(a) Chemical costs
Answer: High

Comments: To control a maximum density Rubber bush infestation you would have to basal bark the plants using Access and diesel. [Note: This would place Rubber bush control in the High ($200- 500/ha) chemical costs category] (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Chemical Costs: Medium Category ($250-$500/Ha) (Chris Brown, pers comm., Regional Weeds Officer – Alice Springs, NT Weeds Management Branch). Chemical costs- Very high (because it is mixed with diesel) (Michelle Kassman, pers comm., Regional Weeds Officer – Barkly, NT Weeds Management Branch).

(b) Labour cost
Answer: High

Comments: [Note: This would place Rubber bush control in the High ($200- 500/ha) labour costs category] (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Labour Costs: Medium. ($100-$250/ha) (Chris Brown, pers comm., Regional Weeds Officer – Alice Springs, NT Weeds Management Branch). Labour costs- High (Michelle Kassman, pers comm., Regional Weeds Officer – Barkly, NT Weeds Management Branch).

(c) Equipment cost
Answer: Medium

Comments: [Note: This equipment would place Rubber bush control in the Low equipment costs category] (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Equipment Costs: Low (Vehicle, or quadbike) (Chris Brown, pers comm., Regional Weeds Officer – Alice Springs, NT Weeds Management Branch). Equipment costs: Low (Michelle Kassman, pers comm., Regional Weeds Officer – Barkly, NT Weeds Management Branch).

A4. What is the general community perception of this weed within the region?
Answer: Medium

Comments: The general community perception of Rubber bush is Medium (all regions) (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007).

Current distribution

B1. What is the current pattern of the species’ distribution across the weed management region?
Answer: Scattered

Comments: Rubber bush’s distribution in the Alice Springs region is scattered (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Rubber bush’s distribution in the Darwin region is scattered (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Rubber bush’s distribution in the Katherine region is widespread (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007).

Persistence

C1. How long will it take to reach the maintenance period?
Answer: Low

Comments: Low. It is likely to take greater than 5 years to reach the maintence period (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007).

C2. What is the minimum time period for reproduction of sexual or vegetative propagules?
Answer: <2 years

Comments: The minimum time for reproduction is less than 2 years (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007).

C3. What is the maximum longevity of sexual or vegetative propagules?
Answer: <2 years

Comments: The maximum longevity of propagules is less than greater than 2 years (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). The seeds were produced in abundance, remaining viable for about two years (Labouriau & Valadares 1976).

C4. What is the threat of reinfestation from outside the management region?

(a) Long-distance (>100m) dispersal by natural means
Answer: Occasional

Comments: Long-distance dispersal of Rubber bush by natural means is likely to be rare (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Seeds are buoyant in water (Grace 2006). Seeds have tufts of long hair which may aid in long distance dispersal. Dispersal is principally by wind and water (Parsons & Cuthbertson 2001).

(b) Long-distance (>100m) dispersal by human means
Answer: Rare

Comments: Long-distance dispersal of Rubber bush by human means is likely to be rare (P. Jeffery, M. Fuller and G. McSkimming, pers comm. 2007). Seeds may be moved in mud sticking to machinery (Parsons & Cuthbertson 2001). Seeds may be moved in mud sticking in the hooves of animals (Parsons & Cuthbertson 2001). Seeds are commonly observed germinating in cattle dung heaps in India (Kumar et al. 1997).

References

Amritphale, D, Gupta, JC & Iyengar, S (1984), 'Germination polymorphism in sympatric populations of Calotropis procera', Oikos, 42, 220-224. Bastin, GN, Ludwig, JA, Eager, RW, Liedloff, AC, Andison, RT & Cobiac, MD (2003), 'Vegetation changes in a semiarid tropical savanna, northern Australia: 1973-2002', Rangeland Journal, 25, 3-19. Díaz, E & Massol-Deya, A (2003), 'Trace element composition in forage samples from a military target range, three agricultural areas, and one natural area in Puerto Rico', Caribbean Journal of Science, 39, 215-220. Francis, JK (2009), Calotropis procera (Ait.) Ait. f., US Department of Agriculture, Forest Service, International Institute of Tropical Forestry, viewed 11th August, <http://www.fs.fed.us/global/iitf/pdf/shrubs/Calotropis%20procera.pdf>. Grace, BS (2006), 'Biology of Australian Weeds 45.Calotropis procera (Aiton) W.T. Aiton', Plant Protection Quarterly, 21, 152-160. Kumar, S, Bagchi, GD & Darokar, MP (1997), 'Antibacterial activity observed in the sees of some coprophilous plants', Pharmaceutical Biology, 35, 179-184. Labouriau, LG & Valadares, MEB (1976), 'On the germination of seeds of Calotropis procera (Ait.) Ait. f.', Anais da Academia Brasileira de Ciências, 48, 236-284. Parsons, WT & Cuthbertson, EG (2001), Noxious Weeds of Australia, 2nd edn, CSIRO Publishing, Melbourne. Smith, N (2001), Not from here: Plant invasions on Aboriginal lands of the Top End, Northern Land Council Centre & Tropical Savannas CRC, Darwin. Smith, NM (2002), Weeds of the Wet/Dry Tropics of Australia: A Field Guide, Environment Centre NT Inc., Darwin.