koster’s curse

Clidemia hirta
leaves (Photo: Forest and Kim Starr,  USGS)
close-up of flowers (Photo: Forest and Kim Starr,  USGS)

Biosecurity Queensland must be contacted within 24 hours 13 25 23.
Biosecurity Queensland Must attend site before any control measure is administered, advise will be provided to the land holder at this time

Common names 
Also known as: clidemia, soap bush,
tropical America
State declaration 
Category 2,3,4,5 - Must be reported to Biosecurity inspector or authorised person. Must not be distributed, moved, possessed or kept under your control.
Council declaration 
As per State Declaration
Known distribution 

Infestations have been found in North Queensland between Mossman and Tully.


Koster's curse prefers tropical climates with an annual rainfall over 1200 mm, growing in both shaded areas and full sunlight. This species prefers humid tropical climates and may invade both disturbed and undisturbed habitats. It is a potential weed of wetter pastures, open grasslands, plantations, roadsides, wetter open woodlands, riparianzones (banks of watercourses), forest margins and rainforests.


Clidemia hirta is a densely branching long-lived (perennial) shrub normally growing 0.5-3 m tall, but sometimes reaching 5 m in height, depending on habitat. In more shaded habitats it grows much taller than it does in exposed areas, where it typically grows less than 1 m tall.

Koster’s curse is a quick-growing invasive plant that has the ability to form dense thickets, smothering native vegetation and causing major problems to primary industries. It forms dense thickets that can smother pasture and native vegetation in a similar manner to lantana. The berries produced are attractive to birds, which can assist the plant spread. It will invade disturbed areas, including the edges of clearings and stream-banks, along fence lines, paths and roadways.

Stem and leaves 

The younger stems are rounded and are covered in large, stiff, brown or reddish-coloured hairs (they are strigose). The oppositely arranged simple leaves (5-18 cm long and 3-8 cm wide) are borne on stalks (petioles) 5-30 mm long. They are oval (elliptic) or egg-shaped in outline with broad end at base (ovate), with pointed tips (acute to shortly acuminate apices), and almost entire (sub-entire) to finely toothed (crenulate or denticulate) margins. Their upper surfaces are sparsely covered in hairs, similar to those found on the stems (they are sparsely strigose), while their lower surfaces and margins are more densely hairy. The leaves also have a somewhat wrinkled (rugose) appearance and five distinct veins that run in an almost parallel fashion from the leaf bases to their tips.

Flowers and fruits 

The flowers are arranged in small clusters in the leaf forks or at the tips of the branches (in axillary or terminal clusters). Each flower is borne on a very short stalk (pedicel) 0.5-1 mm long and has five white, or occasionally pale pinkish, petals (6-11 mm long and 4-5 mm wide). The base of the flower is swollen into a cup-shaped structure (a hypanthium) about 3-3.5 mm long, which is moderately to sparsely covered with a mixture of bristly and sticky (glandular) hairs. The flowers also have five sepals, but these are very small and inconspicuous (about 0.5 mm long), and five distinctive stamens that have a claw-like appearance. Plants flower and fruit prolifically throughout the year, except during dry periods.
The small, rounded (globular), fruit (4-9 mm across) are berries and are either dark blue, purplish or blackish in colour. Each of these berries contains over 100 light brown coloured seeds (0.5-0.75 mm long). These fruit are also covered in stiff spreading hairs, especially when they are young

Reproduction and dispersal 

This plant reproduces by seed, which are principally dispersed by fruit-eating birds. Other animals moving through thickets of this species may carry seeds away with them (e.g. feral pigs) and the fruit are also dispersed by floodwaters. Long distance dispersal may also be brought about by human activities.

Similar species 

Clidemia hirta is quite easily to recognise. Young plants, with their stiff hairs and crinkled leaves, may vaguely resemble a stinging nettle (Urtica spp.), but mature plants can be distinguished by their shrubby habit and white flowers.