Summary:A small tree or coarse shrub to 4 m tall with waxy leaves that have a tuft of hairs at the base of the mid vein. Lots of white milky sap is exuded when the plant is damaged. It has scented, purple and white, somewhat tubular flowers with fruit like, small cabbages. The many seeds have a silky tuft of hairs.
Leaves:Oval, broad and flat in opposite pairs. Thick and hairless apart from a basal tuft. Each pair at right angles to those below. Waxy. Grey-green to blue green with indented bases.
Stems:2000-4000 mm tall. Branched from the base at times and branched higher up. Weak and straight to crooked. Waxy. Copious milky sap exuded when injured. Grey-green. Smooth. Crooked. Soft, thick, corky bark.
Flower head:In groups (umbels) of up to 15 flowers in the upper leaf axils. Outer flowers develop first and inner ones don't develop fully.
Flowers:25 mm wide, scented and white with a deep purple blotch at the base of each petal. Waxy texture.
Fruit:Long and balloon like. Follicle (bladdery pod). Grey-green. 75-120 mm long and almost as wide. Rounded at the base. Tip pointed. Numerous (350-500) seeds are released when the ripe pod bursts.
Seeds:Brown. Flattened. Tuft of long, white, silky hairs at top.
Roots:Taproot, 3000-4000 mm deep. Shallow spreading woody laterals with latex filled canals and a starchy centre that produce suckers when injured.
Reproduction:Reproduces by seed and suckers.
Flowering times:July to October mainly but can flower at any time of year. Fruit mainly ripens from November to February.
Seed Biology and Germination:Prefers to germinate in light conditions and seed germination is inhibited in shaded conditions.
Vegetative Propagules:Crowns and roots form suckers. Broken stems may take root and regenerate.
Origin and History:North Africa, Arabia, Tropical Asia.
Distribution:NT, QLD, SA, WA.
Soil:Prefers sandy soils and alluvial flats along rivers.
Plant Associations:Prefers open overgrazed situations and areas that are disturbed.
Detrimental:Weed of roadsides, watercourses, disturbed areas and pastures.
Toxicity:May cause contact dermatitis.
Symptoms:Latex causes blistering of sensitive skin areas such as the vagina, prepuce or glans penis.
Treatment:Avoid exposing sensitive skin to Calotrope sap.
Legislation:Noxious weed of WA and NT.
Management and Control:Seed is spread by wind and water or mud attached to animals and machinery. Local spread is by seed and suckering from the roots and crowns. Individual plants can be mechanically removed provided the majority of the roots are also removed to a depth of 200 mm. Repeated spraying with picloram plus 2,4-D provides good control. Repeated cultivation provides good control. Buffel grass (Cenchrus ciliaris) inhibits the growth of Calotrope and could be sown as part of a pasture in infested areas.
Herbicide resistance:Biological Control:
Related plants:Calotropis gigantea has similar flowers but they don't have a purple blotch on the petals. In Australia it is a garden ornamental and does not appear to set seed and is spread by cuttings and hasn't become invasive. It is larger being up to 4500 mm tall
Plants of similar appearance:Procera gigantea is the old name for Calotropis gigantea.
References:A.P.B. (1978) Advisory Leaflet No. 36