What is Chromolaena odorata?

Habitat description

Although it tolerates little partial shade, prefers well open areas. C. odorata grows in many soil types but prefers those well-drained (PIER, 2003). It will not grow in waterlogged or saline soils. Requires disturbance to become established and can occur in most tropical and subtropical ecosystems. For best development it requires at least 47 inches (1200 mm) of annual rainfall, but tolerates severe dry seasons (Cruttwell McFadyen, 1989).

General impacts

Forms dense stands which prevent the establishment of other species, both due to competition and allelopathic effects. When dry, is a flashy fuel which promotes fires. It may also cause skin complaints and asthma in allergy-prone people. It is a major weed of plantation crops such as rubber, oil palm, forestry, and coffee, as well as pastureland and recreational parks. C. odorata is not palatable to cattle (PIER, 2003).

Synonym: Eupatorium odoratum L.

Origin: Tropical America

Description

Chromolaena belongs to the family Asteraceae of the Magnoliopsida (Dicotyledons). It is a fast growing shrubby perennial that forms dense bushes about 2.5 to 6 m (8.2 to 19.6 ft.) tall when climbing on other plants. The leaves are lanceolate, pubescent, with a serrate margin, and grow opposite. The stems branch freely and develop lateral branches in pairs. The older parts of the stems are brown and woody near the base; the tips and young shoots succulent with a green to purplish brown color. The root system is fibrous and does not penetrate beyond 30 centimeters (11.8 inches) in most soils. The flower heads are borne in terminal corymbs of 20 to 60 heads on all stems and branches. The flowers are white or pale lilac and when dry have a feathery aspect.

Dispersal methods

The seeds have small spines that can adhere to clothes, fur and feathers, especially when these are wet. (Vanderwoude et. al, 2005 IN: PIER 2003). Appears to readily disperse along waterways downstream from infestations in both the dry and wet ecosystems. Possible factors include the fact that seeds float, and that periodic flood events transport seed. Other dispersal method is by wind (Witkowski and Wilson 2001, IN: Voanderwoude et. al. 2005, IN PIER 2003).

Occurrence

Mostly in disturbed semi-arid and humid areas such as forests, agricultural lands, pasturelands, riparian areas, etc. In Puerto Rico is invading mostly pasturelands in the southern hills and flat lands but it has been observed through the island and the US Virgin Islands. It is used in folklore medicine.

Reproduction

C. odorata has a sexual reproduction although; it is known to reproduce vegetatively. Seed production is very prolific with up to 87,000 seeds per mature plant or about 400,000/sq/m. Some seeds survive for up to 5 years. A plant can germinate and set seed within a 12 month period.

Noxiousness

Considered noxious in 46 states; Guam and the Mariana Islands. Becoming a pest in Puerto Rico.

Control

Physical: Manual slashing causes rapid regeneration unless followed by other methods to suppress it, such as herbicide applications.

Chemical: Some herbicides applied at the seedling stage or early regrowth has given encouraging results but usually the plant resists the first applications. In filed observations in Puerto Rico mature plants have shown resistance to glyphosate and tryclopyr applications.

Biological: The biological control agent Pareuchaetes pseudoinsulata defoliates pure stands reducing the problem to an occasional nuisance.

References

• Liogier, H. A. & Martorell, L. F. 1982. Flora of Puerto Rico and Adjacent Islands: A systematic synopsis. Editorial UPR
• Colin Wilson, 2003. Parks and Wildlife Commission of the Northern Mariana territory & Invasive Species Specialist Group (ISSG) Pacific Islands Ecosystems at Risk (PIER).
• Más, Edwin G. 2007. Personal observations.
• Photos. USDA NRCS Caribbean Area Archives