History and distribution of Chromolaena odorata (L.) R.M. King and H. Robinson   by R.E. Cruttwell McFadyen Queensland Department of Lands Alan Fletcher Research Station P.O. Box 36, Sherwood, 4075 Queensland, Australia  Natural Distribution  Spread to Asia & Africa  Biocontrol Investigations  Future Distribution  References  Figure 1  Figure 2  Table 1 Taxonomic Position Chromolaena is in the plant family Asteraceae or Compositae, which is one of the largest plant families (Table 1). It is a well-defined, very successful family, regarded as the highest i.e. most evolved of the plant families. The Asteraceae are found throughout the world though rare in tropical rain forests, and are particularly abundant in the Americas. Most species are herbaceous; trees are rare. For such a large family, the economic value is low, with relatively few crop plants though many ornamentals (Toelken, 1983). The Asteraceae are divided into 12 to 17 tribes; the Eupatorieae is a well-defined mostly New World tribe, with white, reddish or bluish flowers lacking ray florets (Robinson and King, 1977). Within the Eupatorieae, there are no crop plants or important ornamentals, which is a definite advantage for biological control. Important weed species are Mikania scandens (= micrantha) an important weed in some Old World tropical areas, and Ageratum conyzoides, a common crop and garden weed in the tropics and sub-tropics. The super-genus Eupatorium, before it was split up by King and Robinson in the 1970s, contained over 1200 species, most in the Americas with a very few in Europe, Asia and Africa. Several are important weeds; Ageratina altissima (E. rugosum) in the eastern United States, Ageratina adenophora and Ageratina riparia in Indomalaya to Southern China, South Africa, Hawaii and eastern Australia, Fleischmannia microstemon, a minor weed in the Americas, and Austroeupatorium inulaefolium in Indomalaya and Sri Lanka (Anon., 1983). The genus Chromolaena contains 129 species all from South and Central America and the West Indies (King and Robinson, 1970). Of these, C. ivaefolia and C. laevigata are widespread and occasionally weedy in the Americas, but only C. odorata has spread beyond the New World. It is worth noting here that considerable confusion exists even in published papers regarding the different weed species of Eupatorium. Holm et. al. (1977) included Australia (New South Wales) in the distribution of C. odorata; this is based on a paper by Auld (1977) which lists a specimen of Eupatorium odoratum in the Melbourne herbarium. This specimen, collected by A. Cunningham, has no locality or date and may well have been collected by Cunningham on his 1814-16 voyage to Brazil. This is the sole record of C. odorata from Australia; it has never been found wild there. Holm et. al. (1977, p 214) also cite references for the biological control of "other Chromolaena species in Hawaii and Australia". These were the species Ageratina riparia and A. adenophora; no other Chromolaena species occur outside the Americas or have ever been the subject of biological control programs. This kind of confusion is the understandable result of the adoption of new generic names, compounded by simple misidentifications of plant specimens, but it is important that weed scientists working with the group keep errors to a minimum and avoid repeating old errors. It is particularly important for successful biological control, as the insects of C. odorata do not attack the Ageratina species, and vice versa. Table 1. Families of plants  Family Asteraceae (Compositae)- Cosmopolitan, highly successful: few of economic importance except ornamentals.  Tribe Eupatorieae Well-defined, largely American tribe. Flowers white, reddish, or bluish, without ray florets. Mikania - mostly Brazil. M. scandens (= micarantha) - widespread tropical weed Ageratum A. conyzoides widespread tropical and sub-tropical weed  Super-genus Eupatorium Over 1200 species, mostly American, a few species in Europe, Asia and Africa Ageratina adenophora weed in Indomalaya to Southern China, South Africa, Hawaii and Eastern Australia, poisonous to horses. Ageratina altissima (E. rugosum) weed in Eastern U.S.A., poisonous to livestock and in milk. Ageratina riparia weed in North India, Hawaii and Eastern Australia. Fleischmannia microstemon - weed in Americas. Austroeupatorium inulaefolium weed in Indomalaya and Sri Lanka. Chromolaena odorata Spread of C. odorata: Natural distribution C. odorata occurs naturally over a wide area of the tropical and subtropical Americas, from southern Florida to the northern border of Argentina. There is no evidence of recent spread in these countries nor is the plant a significant or important weed in the New World. It is however one of the more widespread species in the super-genus Eupatorium, most of the other species having quite restricted distributions, and even in the Americas, C. odorata shows some weedy characteristics such as the rapid invasion of cleared forest or abandoned pasture. C. odorata is a herbaceous perennial, which reproduces almost entirely by seed. Where branches lie along wet ground, they will root and very occasionally develop into new plants, but this is of very minor importance. The crown of each plant is single and does not divide even when many-stemmed; suckering from the root does not occur. However, considerable reserves of starch are stored in the root and crown, and plants re-shoot freely after being cut or burnt to ground level. Flowering is photoperiod controlled, even near the equator, and thus occurs synchronously in a region. Flowers develop at the tips of all stems and branches and seed production is prolific. The achenes float on a small stiff pappus and may be blown considerable distances; they also bear short hooks and cling to clothes, hair, etc. once settled. There is no seed dormancy, and germination occurs as soon as there is adequate moisture. Spread into Asia and Africa The accepted view has been that C. odorata was first spread to the Old World via ballast in ships from the West Indies, turning up in Singapore and Malaya in the 1920s (Bennett and Rao, 1968). However, Hooker in 1882 said "E. odoratum ... (is) ... cultivated but very rarely in India" and Prain in 1903 and 1906 stated that it was cultivated 'sparingly' or 'occasionally' in gardens in Central and East Bengal and around Calcutta. It therefore seems more likely that seed from these cultivated plants escaped and gradually spread south into lower Burma and Malaysia and north into Assam (Anon., 1967). However, Konigsberger, Director of the Java Botanical Gardens, in 1912 reported a very vigorous weed in the genus Eupatoria choking out other weeds at Deli in Sumatra (Johnstone and Tryon, 1914) which may have been C. odorata. Deli is a small island at the extreme south of Sumatra, off the eastern tip of Java, and if the weed was present there and not in Jakarta, it must either have been widespread on the east coast of Sumatra by then, or reached Deli via small boats trading along the coast. It was certainly recorded as a major weed in these areas, including Sumatra, by 1940 (Biswas, 1934 and Laan, 1940). It was reported as a dangerous weed in Ceylon in 1944 (Grierson, 1980). Once established in the Bengal, lower Burma and Malaya area, C. odorata spread rapidly throughout Southeast Asia. Much of this spread must have been natural progressive spread as the light wind-borne seeds were blown into new areas. However, with the extensive movements of people, machinery and materials as a result of the Second World War, there must also have been at least some human transport of seeds into new areas. By the late 1960s when the first investigations into biological control began in Trinidad, C. odorata was a major weed in much of Southeast Asia from Mauritius, the south and west coast of India, Borneo and Java to Nepal, Bhutan and, Indo-China, and has since spread to the Philippines (Pancho and Plucknett, 1971), southern China, southern Sulawesi (Desmier de Chenon, pers. comm. 1988) and the Marianas (Figure 1). The first African country to be affected was Nigeria, where the weed appeared in the 1940s. The original introduction was probably via contaminated seeds of Gmelina arboreal a fast-growing forestry tree from Ceylon. By the late 1960s, C. odorata was a major weed in Nigeria and since then, has spread to Ghana, Ivory Coast and Cameroon. C. odorata also appeared near Durban, in South Africa in the late 1940s, from where it spread till it is now a problem throughout the coastal region of Natal, and recently has been found inland in the Transvaal. Biological control investigations C. odorata was already noticed as a serious weed from Assam to Malaya prior to 1940. By the mid-1960s, its rapid spread in West Africa was also causing alarm, and action towards biological control was urged by Drs. Simmonds, Bennett, Rao and others. In 1966, the Nigerian Institute for Oil Palm Research provided funds for the C.I.B.C. to undertake investigations of the insects attacking C. odorata in the Neotropics and to ship suitable insects to Nigeria for field release. I was employed by the West Indian Station initially as a student in 1966 and then as Assistant Entomologist, and these investigations continued until I left Trinidad at the end of 1972. Unfortunately, political and financial problems in Nigeria at the time hindered attempts to rear and release the insects recommended, and only a few and unsuccessful releases of Apion brunneonigrum and Pareuchaetes pseudoinsulata were made in Nigeria in 1970. Later, more successful attempts were made by India, Sri Lanka and Malaysia and these will be presented in the succeeding chapters. Future distribution Figure 2 shows the areas of the world with a tropical (coolest month above 180C) or sub- tropical (warmest month above 220C) humid climate, where the dry season if present occurs in the winter i.e. the summers are hot and wet (Anon., 1980). If this is compared with the present distribution of C. odorata, two facts are obvious. First, in the Americas C. odorata has not spread into the subtropical humid areas while in Asia it has, notably in northern India and Nepal across to southern China. This difference is presumably due partly to competition with the numerous other Eupatorium species occurring in the Americas, and partly to attack by insects and diseases found in the Americas and not in Asia and Africa. The second obvious fact is that all of humid equatorial Africa is under threat from this weed, particularly where the annual rainfall exceeds 1200 mm. In the Pacific area, the islands of New Guinea (Irian Jaya and Papua New Guinea), New Britain, Sulawesi, the Soloman Islands and the islands further west, New Caledonia, Vanuatu, Fiji etc., as well as the north and north- east coasts of Australia, are all climatically suitable for C. odorata. They have escaped so far, but agriculture and weed officials and scientists in these countries need to be aware of the weed and vigilant to destroy any plants that might establish. The Australian Quarantine office is currently producing a warming leaflet about the danger of C. odorata reaching northern Australia; the leaflet will appear in time for the many visitors expected for Expo, and also in time for Thai Airways new Bangkok-Cairns-Brisbane flights, for each new international airport in the humid tropics increases the risk. On the same theme, this talk started with a discussion of the tribe Eupatoriae and super-genus Eupatorium. C. odorata and M. micrantha are the only species to have become widespread weeds of major economic importance, but there are many other species in tropical South and Central America that have equal weedy potential. Agricultural authorities need to be wary of deliberate introductions of new plants, and quarantine authorities need to be aware of possible weed contamination of packing and other material from the Americas. Finally, scientists and officials involved in weed control must react quickly to any reports of a new weed, as initial infestations can be eradicated when still small, but not after several years of seed spread. References Anon. 1967. Identification of Plants on Malayan Rubber Estates: Plates 73-80, Dicotyledons, herbaceous or half-shrubby. Planters Bull. of the Rubber Research Inst. of Malaya 90: 88-89. Anon. 1980. 'The Times' Atlas of the World - Comprehensive Edition 1980, 6th Ed. Times Books Limited, London. Anon. 1983. Important Weeds of the World. 3rd Edition, January 1983. Bayer AG, Leverkusen, Germany. Auld, B.A. 1977. The Introduction of Eupatorium species to Australia. J. Aust. Inst. Agr. Sci. 43: 146-147. Bennett, F.D. and Rao, V.P. 1968. Distribution of an introduced weed Eupatorium odoratum Linn (Compositae) in Asia and Africa and possibility of its biological control. PANS (C) 14: 277-281. Biswas, K. 1934. Some foreign weeds and their distribution in India and Bunna. Indian Forester. 60: 861-865. Grierson, A.J.C. 1980. Compositae in Flora of Ceylon. Vol. 1. Smithsonian Inst., U.S.A. Holm, L.G., Plucknett, D.L., Pancho, J.V., and Herberger, J.P. 1977. The World's Worst Weeds: Distribution and Biology. East-West Center, Univ. Press, Hawaii, USA. Hooker, J.D. 1882. Flora of British India. Vol. 111. Spottiswoode, London. Johnstone, T.H. and Tryon, H. 1914. Report of the Prickly-Pear Travelling Commission, Ist November 1912 - 30th April 1914. Govt. Printer, Brisbane. King, R.M. and Robinson, H. 1970. Studies in the Eupatorieae (Compositae). 24. The genus Chromolaena. Phytologia 20: 196-209. Laan, P.A. Van der. 1940. Motschildluis en Eupatorium als oorzaken van pseudomozaiek. Vlugschr. Dell. Proefst. Medau. 67: 4 pp. Pancho, J. and Plucknett, D. 197 1. Chromolaena odorata (L) R.M. King and H. Robinson - a new record of a noxious weed in the Philippines. Phil. Jour. Animal Science. 8: 143- 149. Prain, D. 1903. Bengal Plants. Vol. 1. Botanical Survey of India, Calcutta. Prain, D. 1906. Contributions to Indian Botany. West, Newman & Co., London. Robinson, H. and King, R.M. 1977. Eupatorieae - systematic review in The Biology and Chemistry of the Compositae. Vol. 1. (eds) Heywood, V.H., Harbome, J.B. and Tumer, B.L. Academic Press, London. 437- 486 pp. Toelken, H.R. 1983. Compositae in Flowering Plants in Australia (eds) B.D. Morley and H.R. Toelken. Rigby Publishers, Adelaide, Sydney. 300-314 pp.