Chromolaena odorata (L.) R.M. King & H. Rob.

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Photo: Costas Zachariades
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Synonyms:	Eupatorium conyzoides Vahl Eupatorium odoratum L.
Common names:	Siam weed (English) Triffid weed (English)
Frequency:	Very rare casual
Status:	Introduced
Description:	Scrambling or climbing shrub, to 4 m (or more when supported). Leaves ovate to triangular, 3-veined from the base, gland-dotted below, smelling strongly of turpentine or paraffin when crushed. Capitula c. 10 × 3 mm, cylindric. Achenes c.5mm, straw-coloured.
Notes:	Cultivated for ornament and now an aggressive weed in many moist, tropical areas of the world; e.g. in South Africa in Mpumalanga and KwaZulu-Natal. This species appears to be a rare casual in Zimbabwe, having been recorded once in Zimbabwe near Chinhoyi in 1967. There are two biotypes which differ on flower colour: the South African one has white flowers and the West African one pale blue. The Zimbabwe specimen is of the West African type (Zachariades, in litt.). The species is somewhat similar to the Crofton weed (Ageratina adenophora), which also has white flowers in corymbose heads. However, these can be separated as follows: C. odorata is a true climbing shrub whereas A. adenophora is a herb, although it may attain 1.5 metres. C. odorata does not have the glandular and purple stems and leaves which A. adenophora has. We are very grateful to Dr Costas Zachariades for informing us of the record, which was published in (Gautier, 1992), for providing us with the photographs of the herbarium material and other information about this species. As far as I am aware, C. odorata is not a weed in the Chinhoyi area. Perhaps the climate was not suitable. McFadyen & Skarratt (1996) published the results of a climatic matching model which indicated that the eastern parts of Zimbabwe and adjoining part of Mozambique are highly suitable climatically for C. odorata. It is in these warm moist areas that we may expect eventually to find Chromolaena. Another interesting observation is that the altitude of Chinhoyi is c.1200m and the hills around it do not seem to attain 1600m; perhaps there is an error here.
Derivation of specific name:	odorata: odorous, fragrant
Habitat:
Altitude range: (metres)
Flowering time:
Worldwide distribution:	North, Central and South America (SE USA to northern Argentina)
Zimbabwe distribution:	N
Growth form(s):
Endemic status:
Red data list status:
Insects associated with this species:
Spot characters:	Display spot characters for this species
Literature:	Burrows, J.E., Burrows, S.M., Lötter, M.C. & Schmidt, E. (2018). Trees and Shrubs Mozambique Publishing Print Matters (Pty), Cape Town. Page 1031. (Includes a picture). Gautier, L. (1992). Taxonomy and distribution of a tropical weed: Chromolaena odorata (L.) R. King and H. Robinson Candollea 47 McFadyen, R. & Skarratt, B. (1996). Potential distribution of Chromolaena odorata (Siam Weed) in Australia, Africa, and Oceania. Agriculture, Ecosystems and Environment 59 Zachariades, C., Janse van Rensburg, S. & Witt, A.B.R. (2013). Recent spread and new records of Chromolaena odorata in Africa Proceedings of the Eighth International Workshop on Biological Control and Management of Chromolaena odorata and other Eupatorieae, Nairobi, Kenya, 1-2 November 2010. ARC-PPRI, Pretoria Pages 20 - 27.

Other sources of information about Chromolaena odorata:

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Flora of Caprivi: cultivated Chromolaena odorata
Flora of Mozambique: Chromolaena odorata

External websites:

African Plants: A Photo Guide (Senckenberg): Chromolaena odorata
BHL (Biodiversity Heritage Library): Chromolaena odorata
EOL (Encyclopedia of Life): Chromolaena odorata
GBIF (Global Biodiversity Information Facility): Chromolaena odorata
Google: Web - Images - Scholar
iNaturalist: Chromolaena odorata
IPNI (International Plant Names Index): Chromolaena odorata
JSTOR Plant Science: Chromolaena odorata
Mansfeld World Database of Agricultural and Horticultural Crops: Chromolaena odorata
Plants of the World Online: Chromolaena odorata
Tropicos: Chromolaena odorata
Wikipedia: Chromolaena odorata