Chromolaena odorata (L.) King & Robinson (Asteraceae)

Eupatorium odoratum L.

A widely distributed neotropical shrub introduced to many parts of the tropics. Forms pure stands in disturbed areas, grasslands, fallows and forestry plantations. Species spreading rapidly due to its efficient short- and long-distance dispersal abilities.


Species characteristics

Life form, size, lifespan

Multi-stemmed shrub to 2.5 m tall in the open and to 10 m tall when climbing vegetation.

Taxonomy, variation and plasticity

The invasive populations of C. odorata in Asia and southern Africa, both originating from the Caribbean, are morphologically different.

Reproductive biology

Sexual reproduction starts when the plants is one year old. Terminal cymes bear around 70 insect-pollinated flowers. The small fruits (weight: 0.2 mg) mature in about a month. A dense thicket of C. odorata may produce about 109 seeds ha-1 in Ivory Coast and has a very large seedbank. Fruits (cypsella) are typically wind-dispersed as dry and windy weather is necessary for fruit release, however animal dispersal is possible thanks to the fruits small hooks. Flowering initiation appear to be mainly related to the onset of the main dry season and last for three to five months. Seed germination is favoured by water and light and therefore takes place at the start of the rainy season. In India seed dispersal and germination occur before (April-May) and at the start (May-June) of the rains respectively. Active growth takes place through the rainy period until October and is followed by flowering. Seed reach maturity in March.

Resilience and resistance

Shoots may root when touching the ground. It possess an underground 'organ' which ensure the plant's survival in case of fire, drought or mechanical damage through coppicing.

Environmental requirements and successional status

Frost intolerant and is adverse to dry regions. Flourishes in disturbed habitats, particularly in areas of slash an burn agriculture. In Trinidad (native range) on open land C. odorata is a successional species which supersedes the pioneer ephemeral herbs, then is displaced by shrubs and small trees and dies as soon as the forest canopy closes.

Products and uses

Ornamental plant appreciated for its winter flowers. In the West Indies it is known as the 'Christmas bush'. Formerly thought to be useful in controlling coarse grasses, mainly Imperata spp.


Status in native range

Range and abundance

Wide distribution in the neotropics from the USA (29o N) to Argentina (31o S) including most of the West Indian islands.

Climate

Tolerates a variety of temperate and tropical climates. In South America on the western side of the Andes the species does not spread south of 7o S as the conditions are to dry.

Site requirements

Grows from sea level to 1000 to 2800 m. It occurs on open freely-drained grounds and is absent in natural forests.

Weediness

Site density appears to have increased since last century as a result of human's impact on the environment.

Pests and diseases

Over 240 arthropods have been recorded on C. odorata in Trinidad where the species was investigated in detail for potential biocontrol agents.


Status in invaded regions

History of introductions and intensity of invasions

Introduced to botanical gardens of Dacca (India), Java and Peradeniya (Sri Lanka) in the 19th century and for ornamental reasons in Southern Africa early 20th century. In Western Africa the plant was accidentally introduced with forestry seeds in Nigeria in 1947 and was deliberately introduced to Ivory Coast in 1952 to control Imperata spp. following a recommendations by the famous botanist Auguste Chevalier. In 1994 small infestations of C. odorata were found in Queensland, Australia and it is suspected that the introduction resulted from contaminated pasture seeds from overseas. Introduced and spreading on a number of tropical islands and is also found in a number of temperate regions.

Patterns of invasion and time-lag

In Indian fallows C. odorata recruitment peaks after 3 years and ceases in 10 to 20 years old fallows. Seedling mortality is higher in older fallows and plant vigour decreases after 5 years. Thus the duration of fallows will greatly affect the local abundance of C. odorata. Elsewhere in India in established vegetation C. odorata's survivorship was only 1.4 % in the first year's cohort but much higher in older individuals. Still, despite the high mortality this resulted in a 30% increase in population size in one year. In an Indian monsoon forest C. odorata regenerated freely in selection-felling gaps but was absent from treefall gaps in undisturbed forest. In slash and burn rice cultivation in Ivory Coast forests the fields, if cultivated for only one year, will quickly be filled with pioneer trees after abandonment whereas after 3 years C. odorata will become dominant. Most seed dispersal is local, however, as the seeds have small spines and can cling to fur, feathers and clothes, long distance dispersal is possible. Seeds can also travel great distances with contaminated crop plants or vehicles. In Australia dispersal appear to have also included water, cattle, horses, feral pigs and sugar cane harvesting equipment. No time-lag has been reported.

Site and climate

Distribution limited by rainfall but no absolute minimum exist. The species is generally not present in areas with <1200 mm of rainfall a year and occurs predominantly at altitudes below 1000 m. The species does not appear to have special soil requirements.

Floristic region and vegetation types

Associated with local weeds or secondary vegetation of disturbed areas.

Pests and diseases

In Ivory Coast only insects feed on C. odorata with little impact on the species.

Impact on ecosystem

In Western Africa C. odorata suppresses regeneration of tree species in areas of shifting cultivation if its become well-established. In southern Africa it reduces species diversity and the plants flammability poses a threat to forest edges.

Impact on humans and related activities

C. odorata is a problem in agricultural land and commercial plantations.

Control

In several tropical countries biological control, using a defoliating artiid, was initiated in the early 1970s generally without success at the exception of Sri Lanka and in the 1980s of Guam. To date only one species has been tried for biological control. An eradication programme has been initiated in Australia using herbicide.


Ecological differences

Existence of ecological equivalent species and competitive interactions in invaded regions

Grows faster than native pioneer species in Ivory Coast.

Differences in status and ecology between invaded and native ranges

Apart from the apparent higher pest problem in the native range no evidence is available.


Selected references

* Chandrashekara, U.M. & Ramakrishnan, P.S. (1994) Successional patterns and gap phase dynamics of a humid tropical forest of the Western Ghats of Kerala, India: ground vegetation, biomass, productivity and nutrient cycling. Forest Ecol. Manage. 70, 23-40.
Cruttwell McFadyen, R.E. (1988) Ecology of Chromolaena odorata in the neotropics. In Muniappan, R. (Ed.) Proc. First Int. Workshop on biological control of Chromolaena odorata, pp. 13-20. Bangkok.
** Cruttwell McFadyen, R.E. & Skarrat, B. (1996) Potential distribution of Chromolaena odorata (siam weed) in Australia, Africa and Oceania. Agric. Ecosyst. Environ. 59, 89-96.
** Gautier, L. (1992) Taxonomy and distribution of a tropical weed: Chromolaena odorata (L.) R. King & H. Robinson. Candollea 47, 645-662.
* Gautier, L. (1993) Reproduction of pantropical weed: Chromolaena odorata (L.) R. King & H. Robinson. Candollea 48, 179-193.
* Ivens, G.W. (1974) The problem of Eupatorium odoratum L. in Nigeria. PANS 20, 76-82.
* Kushwaha, S.P.S., Ramakrishnan, P.S. & Tripathi, R.S. (1981) Population dynamics of Eupatorium odoratum in successional environments following slash and burn agriculture. J. appl. Ecol. 18, 529-535.
** Rouw, A. de (1991) The invasion of Chromolaena odorata (L.) King & Robinson (ex Eupatorium odoratum), and competition with the native flora, in a rain forest zone, south-west Cote d'Ivoire. J. Biogeogr. 18, 13-23.
* Yadav, A.S. & Tripathi, R.S. (1981) Population dynamics of the ruderal weed Eupatorium odoratum and its natural regulation. Oikos 36, 355-361.

Pierre Binggeli

May 1997