The genus Bidens (Compositae) is composed of approximately 230 species having a worldwide distribution in tropical and temperate regions. It is primarily a continental group, which has become established on some islands, notably the Hawaiian islands. The centers of diversity are Africa and the New World, with each center having about 100 species. Several species are so abundant that they are considered serious weeds. Two will be of particular concern here: Bidens alba var. radiata (Schultz-Bip.) Ballard and B. pilosa var. minor (Blume) Sherff, another member of the complex. B. alba var. radiata (smooth beggar-tick) occurs in south eastern Mexico into Central America and in Florida, U.S.A.; B. pilosa var. minor (hairy beggar-tick) is primarily restricted to Central America (Ballard 1986).
B. pilosa var. minor and B. alba var. radiata are erect annual herbs with opposite pinnate leaves. Flowers are organized into a capitulum with yellow disc flowers and five or six white (occasionally purple) ray flowers which are 5-7 mm long and have a nonfunctional style in the former species and ray flowers 15-18 mm long with no style in the latter. Both plants, in common with most species of Bidens, are found in moist, disturbed areas. Mature plants are easily recognized by the spherical heads radiating black, barbed seeds in all directions from the receptacle. The two species are cross-fertile, although B. alba var. radiata is a tetraploid (x = 24) and B. pilosa var. minor is a hexaploid (x = 36) (Ballard 1986; Norton unpubL). Hybrids are fertile pentaploids (x = 30) which are intermediate for flower size, hairiness, time of flowering, and leaf polyacetylene level (unpubl). The base chromosome number for most species of Bidens appears to be x = 12, although many species are tetra- and hexaploid.
Although normally not thought of as a significant biomedical resource, several species of Bidens have attained widespread use in folk medicine, or in one case agriculturally, and have been investigated by modern chemical methods. Biologically active constituents have been isolated, characterized, and tested as single compounds against a spectrum of organisms. In this review some of the ethnopharmacology of Bidens will be discussed along with the results from modern methodology assessing biological activity. Results for two tissue culture systems for producing some of the compounds shown to be of interest will also be presented.
Traditional Uses of Bidens
Bidens pilosa is a major weed in Africa and Latin America, seriously affecting yields of maize, dryland rice, cereals, coffee, and tea. Holm et al. (1979) list 20 species of Bidens that are considered important weeds. Bidens pilosa is the most widespread; with documented occurrence in 59 countries around the world. It is especially a problem in agriculture in the humid tropics in the Central American lowland (Campbell et al. 1982). However, in the tropics, B. pilosa and the segregate species B. alba are also widely used as medicinal herbs. This is not without its risks, however, Rose and Guillarmod (1974) note that B. pilosa leaves are boiled and eaten as a vegetable with maize and spinach as the staple diet in parts of the Transkei region of South Africa. However, this region is known to have a high incidence of esophageal cancer. Studies by Mirvish et al. (1985) show that ground-dried leaves of B. pilosa acted as a weak cocarcinogen when added to the diet of rats along with methyl-n-amylnitrosamine (MNAN), a known cocarcinogen for papilloma and carcinoma of the esophagus. B. pilosa is used in parts of Central America in traditional medicine for treatment of wounds and such (see Table Uses and biological activities of Bidens spp.) but it is also sometimes mixed with half-boiled rice and fermented to make a kind of saki.. Morton (1962) reports on the appeal of B. pilosa as a food plant. In this connection it should be noted that B. pilosa has relatively high levels of niacin, important in diets depending on maize; lysine levels are also relatively high.
Table Uses and biological activities of Bidens spp.
|Species (locale)||Use/sensitive organism||Plant part or compounds tested|
|(P.R. China)||Rheumatism, weakness,|
|Hawaii||Tea, blood purifier treatment for thrush||Leaf|
|Mosquito larvae||Defatted etoh extract|
|Candida albicans||All parts|
|Escherichia coli,||Leaf: ether|
|Staphylococcus aurea||extract saline|
|Periplanata americanus (roach)||Stem, leaves, flowers|
|Candida albicans||Root, seed|
|Seed germination/||Soil, plant|
|root growth (lettuce, radish, cucumber)||extracts|
|(P.R. China)||Wounds and ulcersa||Leaf|
|(Mexico)||Food, agricultural system||Leaf, plants|
|(Central Am.)||Wounds, rheumatism, colds, hepatic, infections, saki||Various parts|
|Various bacteria||Whole plant extract|
|Insect antifeedant||Various parts|
|Food, high niacin level||Leaf|
|(Uganda)||Food, flavoring herb||Leaf, stem|
|Analgesic, anti-pyretic, anti-inflammatory||Leaf|
|Bacteria, yeasts, filamentous fungi, Skin fibroblasts||PHT|
|Cryptococcus laurentii||PHT, PDE-OAc,|
|Candida albicans||PDE, ETE and and others PA’s|
|Drosophila melonogaster eggs||PHT|
|Yeasts, filamentous fungi, various bacteria||Various PA’s|
|Mosquito larvae||PHT, PDE|
|E. coli, S. ceriviseae||PHT|
|Antitumor||Defatted Etoh extract|
|B. trinervia||Candida albicans||All parts|
|Candida albicans||All parts|
Within the genus Bidens few investigations of natural products have focused on compounds other than the polyacetylenes which are characteristic of the Compositae. Only flavonoids and the related anthochlor pigments (chalcones and aurones) have otherwise been reported. Since there has been considerable recent interest in the bioactivity of polyacetylenes and their sulfur derivatives, thiophenes and thiarubrines, the occurrence of this group of compounds in Bidens is emphasized here.
Polyacetylenes, also termed polyines or acetylenes, are found in 19 higher plant families and in basidiomycete fungi. They are most characteristic of members of the Umbelliferae, Compositae, Santalaceae, and related families. Higher plants account for 85% of the known compounds, with the remainder isolated from fungi. Over 725 known acetylenes have been described. In recent years studies on the bioactivity of many of these compounds have shown that some have powerful phototoxic antibiotic activities with potential for application in pest control.
Bidens: Conclusions and Prospects
Three aspects of species of Bidens of possible relevance to biotechnological and/or biomedical applications are:
1. Species of the plant are troublesome weeds in many parts of the world; however, the same plants find use in folk medicine for a variety of ailments. Whether the preparations are really efflcaceous in most of these uses is certainly doubtful, but the folk remedy for thrush, an infection of children caused by Candida albicans, is evidently on a sounder basis, since one of the likely components of the plants used, PHT, has been shown in several studies to be toxic to the fungus (Table Uses and biological activities of Bidens spp.).
2. Controlled studies of a wide variety of polyacetylenes have demonstrated the toxicity of these compounds to a number of pathogenic and nonpathogenic microorganisms. Two compounds, PHT and a-terthienyl, have been tested extensively and found to be lethal to a wide range of organisms at levels that could be practical for application to water areas as mosquito larvicides or other pesticide. Selectivity at the level of microorganisms seems to depend largely on the presence or absence of a lipid component in the cell wall.
3. Two species of Bidens are adaptable to producing their characteristic compounds in either crown gall cultures or root cultures. As sources of compounds only the latter can be proposed on any reasonably economical basis. Root cultures of B. alba grow rapidly and produce a good yield of the root polyacetylenes. They can also be manipulated to produce compounds not normally found in them but at a sharply decreased yield. Evidently differentiation is necessary for the compartmentalization that leads to efficient synthesis. How to use these cultures? The most immediate use could be for metabolic studies; there are still many questions unanswered about polyacetylene metabolism, not the least of which is the enzymology of the formation of the triple bond. Another possibility is for small-scale production of the major acetylenes produced by the roots; root cultures of Eriophyllum lanatum have been used in this way.
Still another use could be biotransformation of polyacetylenes to novel structures normally not occurring in the plant or, possibly, in other plants. These compounds could then be used for toxicity studies. To the author’s knowledge, no work has been done on the use of inhibitors of any of the steps of polyacetylene synthesis. Given the toxicity of some of these compounds, it is possible that the right inhibitors could cause the build-up of an intermediate highly toxic to the host plant. This could be the basis for a species-specific herbicide for these plants. Finally, it is interesting that B. pilosa, which owes its survival to its ability to rapidly colonize available ground — the qualities which make it a pernicious weed (along with allelopathic compounds), should prove so readily adaptable to callus and root culture.
Selections from the book: “Medicinal and Aromatic Plants III”, 1991.