The use of medicinal plants was known to the most ancient civilizations. Sanskrit texts tell about the gathering of plants for medicinal purposes. Also the Assyrians and Babylonians were familiar with them, as well as the Egyptians. In texts from before 1600 BC the use of plants are described. The ancient Greeks knew many medicinal plants as one can read in the scripts of Aristoteles, Hippocrates, Pythagoras, and Theophrastos. The Romans also had profound knowledge of this subject as is shown in the work of Dioscorides from 77 BC, the Materia Medica, in which all medicinal plants known at that time are described. This book has been a guide for 1500 years. In medieval Europe the signature theory was developed, stating that one could read from the shape and characters of a plant, the organ for which the plant had medicinal powers. As a result names like lungwort, Pulmonaria officinalis; liverleaf, Hepatica nobilis; and eyebrights, Euphrasia sp., originated. Walnuts, Juglans regia, would cure headaches, because of their resemblance with brains. Strong supporter of this theory was Theophrastus Bombastus von Hohenheim (1493-1541), better known as Paracelsus.
At this time also illustrated herbals appeared. Printed herbals date from the last quarter of the 15th century; the first illustrated specimen appeared in 1526. In 1555 the ‘Cruydeboek’ of Dodoens (or in Latin Dodanaeus) was published in Antwerp and was soon translated into French. In 1640 an English herbal appeared, describing some 3800 plants. After this, botany gradually developed into a science with new ideas and views. Slowly, medicinal plants were replaced by medicines with purified or synthetically obtained active substances. However, in countries where medical care and medicines are hardly available, like in developing countries, herbs stay the only source of health care (Medicinal plants 2).

Today, the pharmaceutical and chemical industry only use plants to isolate certain active substances, e.g., pyrethrum, Chrysanthemum cinerariaefolium; and derris, Derris eppiltica, are grown on a large scale for pyrethrine and retenone, which are used in insecticides. Other substances derived from plants are alkaloids, glycosides, aromatic substances, sterols and terpenes. Alkaloids were the first to be isolated and include substances that act like anaesthetics, sedatives, and stimulants, and others that bring about muscular relaxation and hallucinations. Nowadays over one hundred different alkaloids are known. Many are used as the active ingredient of stimulants (see there). Quinine from the bark of the quinine tree (Cinchona sp.) was of medical importance because of its effect in curing malaria.
Valeriana officinalis, valerian, (Medicinal plants 3) contains an active ingredient used for nervous afflictions. It is a widely used in self-medication.
Glycosides are compounds with a sugar component, they are applied in medicines for heart failure. Aromatic oils often have an antiseptic or antibacterial effect. Sterols are used in contraceptives. Terpenes are the main substances of essential oils (see there).
A number of plants are used in herbal teas or beverages to cure infections and to improve the resistance, like chamomile, Matricaria chamomilla (see Chrysanthemum cinerariaefolium) (Medicinal plants 1). It is beyond the scope of this program to go into details for this group of plants.