Medicinal Plants. Short Description

Founding myths in all great civilizations mention medicinal plants. One of the Chinese mythical emperors, Shennong (the Divine Husbandman), is presented as the ancestor of Chinese drug lore as well as the ancestor of agriculture. In the Huainanzi, a text from the second century все, it is said that “he tried all herbs; in one day he found seventy that were toxic." His name was also invoked in the title of the first Chinese drug compendium, composed in the first century ce, the Shennong bencaojing (Shennong's Classic of Medical Material).

The close relation between foodstuffs and medicinal plants, on the one hand, and the ambivalence of every drug (with both toxic and beneficial potential effects), on the other hand, is illustrated by these points. The same ambivalence is emphasized by the Greek term pharmakon (poison and remedy).

However, the presence of medicinal plants in founding myths underlines the importance of the natural products in daily life and in the representations of nature as early as the beginning of human history and probably of human prehistory. Recent researches have even suggested that nonhuman primates acquire the ability to use medicinal plants (zoopharmacognosy). For instance, chimpanzees, when sick, have the habit of chewing the pith of Vernonia amygdalina (with antibiotic, antitumor activity) or swallowing the leaves of Aspilia species (killing parasitic worms).

The large body of botanical medicine books written in various civilizations since antiquity has shown an important accumulated knowledge of medicinal plants, their gathering, pharmaceutical processing, properties, and medical indications. According to many Mesopotamian clay tablets, diseases were cured, as soon as the first half of the third millennium все, with numerous fresh or dried simples (medicinal plants or a vegetable-based drug); more than 850 plant medicines are listed by the ancient Egyptians in the Ebers papyrus (c. 1500 все), including such drugs as aloe, castor bean, garlic, and juniper berries.

Many centuries later, the great tradition of materia medica treatises was initiated by the Greek physician Dioscorides's De Materia medica (first century ce), a precise description of about six hundred plants, with their properties, uses, side effects, and cultivation. It was the major standard reference through the Middle Ages and the Renaissance in Europe. The development, during the Renaissance, of botanical illustrations and the addition of exotic plants to the therapeutic arsenal are also noteworthy.

At the end of the sixteenth century in China the huge Bencao gangmu (Classified Medical Material), by Li Shizhen (1518-1593), was printed. Plants form the most important part of the text, with 1,094 out of 1,895 kinds of drugs, the plant kingdom being divided into five sections: herbs (including wormwood, rhubarb, and aconite), grains (hemp, wheat, rice, etc.), vegetables, fruits, and trees.

Therapeutic properties have a great diversity, and some plants are regarded as a panacea, often in relation with the Doctrine of Signatures, developed implicitly in China and explicitly in Europe by German alchemist Paracelsus (1493-1551). This is the case with one type of ginseng, the branched roots of which evoke a human body.

The Doctrine of Signatures suggests that the medical effects of a plant can be detected by its shape, color, taste, or ecological conditions of growth. For instance, the red color of a leaf is a “sign" of an effect on blood circulation, and the fact that willows (Salix sp.) or Filipendula ulmaria grow in moist and cool conditions could be interpreted as a "signature" of a possible use for feverish illnesses or rheumatism. The latter example is quite curious because these plants owe their properties to the presence of salicin and other salycilate compounds, the origin of aspirin (acetylsalicylic acid), one of the most-used drugs for pain, fever, and inflammation.

Ethnobotanists (people who study the plant lore of a culture) collect and preserve the knowledge of medicinal plants available in cultures that have no written sources. It is estimated that more than twenty-two thousand plants (often up to 80 percent of the substances used to cure diseases) are used by traditional medicines, and an important part of the world population still entirely depends on these natural drugs as remedies.

Since the nineteenth century Western biomedicine (except homeopathy, which is a system of medicine that treats a disease by the administration of minute doses of a remedy that would in healthy persons produce symptoms similar to those of the disease) has rejected the ancient practices of polypharmacy (prescriptions of many plants together), preferring instead the isolation of active secondary compounds (alkaloids, flavonoids, terpens, etc.) from plants and their industrial production by chemistry.

Morphine was isolated from opium in 1805 by Friedrich Sertürner, and quinine isolated in 1820 by Pierre Joseph Pelletier and Joseph Bienaime Caventou from Cinchona (any of a genus of South American trees and shrubs whose dried bark was used to treat malaria). Today 40 to 50 percent of all medical prescriptions in Europe and the United States contain at least one plant-derived ingredient, and medicinal plants are of extreme importance as a source of potential medicines. For instance, more than seventy alkaloids have been isolated from a little herb, the Madagascar periwinkle (Catharanthus roseus), and some of them are effective against leukemia and other cancers.

The problems of "new" diseases and drug- resistant strains of diseases make essential the research of new drugs from the vegetable kingdom. Traditional knowledge in this way is useful: The leaves of Artemisia annua, a wormwood mentioned as a drug for fevers in Chinese texts from the fourth or fifth century ce, are now the source of artemisinin, a compound with major antimalarial activity used as an alternative to chloroquine.

A systematic medicinal screening of tropical plants could allow the discovery of new compounds not used in traditional medicines. However, the overexploitation of numerous drugs (Panax ginseng or Eucommia ulmoides, for instance) may lead to their disappearance. Above all, the dramatic reduction of biodiversity (biological diversity as indicated by numbers of species of animals and plants) around the world is a serious threat to the future research of new drugs: There is a crucial mandate now adopted by many health-related organizations worldwide: "Save the plants that save lives."