Lecture 14. Medicinal plants

Summary

There is no global estimate of how many plants are used medicinally, but the number must in the tens of thousands, considering that:

• In Mexico, there are approximately 3500 species of medicinal plants, according to Edelmira Linares of the Botanical Garden of the National Autonomous University of Mexico.
• Traditional healers in China have used more than 5000 species of plants
• Ayurvedic and other traditional healers in South Asia use at 1800 plant species
• In most cultures, a high percentage of useful plants are medicinals

Prescription drugs draw heavily on traditional herbal healing:

• One quarter of the prescription drugs sold in the United States, Canada and European countries contain active ingredients derived from plants
• The global over-the-counter value of plant-derived drugs is estimated at more than US$40 billion per year

Consumption of traditional herbal remedies is apparently increasing around the world:

• The Food and Agriculture Organization estimates that between 4000 and 6000 species are traded internationally
• The demand for herbals (nutraceuticals) in the United States and Europe is booming; the retail market value of herbal medicines has increased from US$1.5 billion in 1992 to over US$4 billion in 1998
• Chinese medicinal plants are particularly popular, accounting for 30% of exports

Biodiversity prospecting and overharvesting are major issues facing people involved in production and consumption of herbal remedies and plant-derived drugs:

• Fewer than one percent of all plant species have been screened for bioactive compounds
• Some researchers estimate that the 50 major plant-derived drugs on the market represent only about 12 percent of medically useful compounds in the rain forest, whereas other scientists believe that most or all of the major naturally-derived pharmaceuticals have already been discovered
• Shaman Pharmaceuticals (in South San Francisco), an industry leader in using ethnobotanically directed bioassays of plants and setting terms of reciprocity for local people in developing countries, has recently changed its focus from plant-derived pharmaceuticals to herbal remedies
• Increased demand for plant-derived drugs and herbal remedies is leading to the overharvesting of vulnerable species, a situation being monitored by the IUCN Medicinal Plants Specialist Group

Examples:

• The Rubiaceae, a large family of about 550 genera and over 9000 species, is cosmopolitan, though mainly found in the tropics and subtropics with a few species in the temperate and cold regions. They are trees, shrubs, vines and a few herbs, with opposite or whorled leaves that are simple and entire; stipules are always present and often conspicuous. The flowers are bisexual and regular, with four or five free sepals and four or five fused petals. The ovary is inferior, with one to two locules. The inflorescences are panicles, cymes or aggregated heads. The fruit is a capsule, berry, drupe or schizocarp. Main economic products from the Rubiaceae are coffee (from Coffea arabica and C. robusta), medicines, dyes and many ornamental flowers (including Gardenia and Ixora). One of the best known medicinal plants is Cinchona officinalis and other related species (Jesuits’ bark, Peru bark and other names), the source of the antimalarial quinine. Cephaelis ipecacuanha (ipecacuahna) was much collected in various parts of Latin America and cultivated in Malaysia for its dried rhizome, used medicinally as an expectorant.

• The Apocynaceae (now containing the family Asclepiadaceae) contains some 355 genera and 3700 species that are found throughout the subtropics and tropics, especially in rain forest regions; some genera extend into temperate zones. They are plants with milky latex, which have simple, opposite or whorled leaves. The flowers are bisexual, regular and are often large, showy and fragrant; they usual consist of five sepals (free or fused) and five petals fused in a tube with five lobes. The ovary is inferior or half-inferior, formed of two united or free carpels. The fruits are paired and fleshy (splitting or not) or dry (splitting). Most species are toxic, and many are used medicinally. The rosy periwinkle (Catharanthus roseus) is a cultivated ornamental with 67 named alkaloids, notably vincristine and vinblastine, used in the treatment of certain forms of childhood leukemia. Rauvolfia serpentina and other species are the source of reserpine, which reduces high blood pressure and is used in the treatment of mental illness. The family is also known for its ornamentals, including Allamanda, Asclepias (butterfly weed), Hoya (wax plant), Nerium (oleander), Plumeria (frangipani) and Vinca (periwinkle).

• In the Scrophulariaceae, the genus Digitalis contains glycosides that have a strong effect on the cardiovascular system. The Scrophulariaeae is now included in the Plantaginaceae, a cosmopolitan but mainly temperate family of 114 genera and 2100 species. The family is best known for its ornamental flowers, from species of Antirrhinum (snapdragons), Calceolaria (slipper flower), Mimulus (monkey flower), Penstemon (beardtongue), Russelia (firecracker plant) and Veronica (speedwell).

Readings:

Berlin, E.A. and B. Berlin. 1996. Medical Ethnobiology of the Highland Maya of Chiapas, Mexico: the Gastrointestinal Diseases. Princeton, Princeton University Press.

Hobhouse, Henry 1992. Seeds of Change: Six Plants that Transformed Mankind. London, Papermac. Especially pages 3 – 52, Quinine and the White Man’s Burden.

Joyce, C. 1994. Earthly Goods: Medicine Hunting in the Rainforest. Boston, Little, Brown

Plotkin, M.J. 1993. Tales of a Shaman’s Apprentice: An Ethnobotanist Searches for New Medicines in the Amazon Rain Forest. New York, Viking.

Prance, G.T., D.J. Chadwick and J. Marsh. 1994. Ethnobotany and the Search for New Drugs. Chichester, Wiley.

Schultes, R.E. and R.F. Raffauf. 1990. The Healing Forest: Medicinal and Toxic Plants of the Northwest Amazonia. Portland, Dioscorides Press.

Questions for discussion:

• Which plant families would you rank as the most "medicinal" in the world, and what data exists to support your opinion?
• What is the likelihood of discovering major new pharmaceutical products in the plants of your country?
• In any one culture, do you think that we can distinguish medicinal plants or illnesses that are "naturalistic" (derived from natural, usually visible reality) and those that are personalistic (related to nonvisible, extranatural phenomena), or is this a false dichotomy?

Perspective for discussion:

"In the traditional medicine of the highland Maya, as with many other ethnomedical systems, the maintenance or reestablishment of a state of health is dependent on events and interactions in two separate realities: the natural, usually visible, reality that follows predictable physical norms, and a frequently nonvisible reality that relates to extranatural phenomena. We adopt Foster’s (Foster and Anderson 1978) dual division of medical systems into naturalistic and personalistic to characterize these two cognitive frameworks.

In the naturalistic system, a health condition is empirically determined and is based primarily on immediately apparent signs and symptoms. For a naturalistic … it is the norm that one treats oneself with medicinal plants or, lacking this knowledge, consults with individuals who are themselves knowledgeable about such plants.

In contrast, diagnosis of personalistic conditions is based on retrospective presumption of etiologic agent… Diagnosis and treatment frequently involve the intervention of healers with special powers, such as a pulser or diviner. While personalistic conditions may at times also be treated with herbal medications, Maya curers normally employ remedies that require ceremonial healing rituals and special prayers."

From Berlin, E.A. and B. Berlin. 1996. Medical Ethnobiology of the Highland Maya of Chiapas, Mexico: the Gastrointestinal Diseases.

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