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).
Figure 1. C. Odorata growth habit.
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).
Technical name:Chromolaena odorata (L.) King & Robinson
Synonym: Eupatorium odoratum L.
Common names: English: Bitter bush, Jack in the bush, Chromolaena, Siam weed, Triffid weed Spanish: Cariaquillo Santa Maria, Santa Maria
Origin: Tropical America
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
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).
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.
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.
Figures 2 & 3. C. odorata inflorescences.
Considered noxious in 46 states; Guam and the Mariana
Islands. Becoming a pest in Puerto Rico.
Physical: Manual slashing causes rapid regeneration
unless followed by other methods to suppress it, such as herbicide
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.
Liogier, H. A. & Martorell, L. F. 1982. Flora
of Puerto Rico and Adjacent Islands: A systematic synopsis.
Colin Wilson, 2003. Parks and Wildlife
Commission of the Northern Mariana territory & Invasive Species
Specialist Group (ISSG) Pacific Islands Ecosystems at Risk
M�s, Edwin G. 2007. Personal observations.
Photos. USDA NRCS Caribbean Area Archives
For more information, contact Edwin M�s at 787-766-5206.