While humans suffered in olden times from innumerable maladies and diseases, they experimented with plant cures. But how would they know what plant to use? Out of frustration probably developed the concept of the plant "signature." Religious people taught that God provided visual cues, because plants were placed on earth for the good of mankind. The key to human use of plants was hidden in the form (signature) of the plant itself, so look closely for the label from God that permits us to recognize and utilize these plants for the benefit of life.
Signature plants were probably first recognized in ancient China, where there was a classification that correlated plant features to human organs.
Yang (primitive male) was associated with strongly acting plants; ailments of the upper half of the body were treated with upper parts of plants. Yin (primitive female) was associated with plants having moderate action and those with bitter, sour, salty, and sweet tastes; ailments of lower parts of the body were treated with below-ground plant parts.
In Western cultures signature plants emerged for medical uses during the Middle Ages, when people believed that human destiny was determined by the stars (astrology) and everything upon the earth was erected for the sake of mankind. Each plant had magic (power) either to benefit or to destroy us.
The most famous advocate of signature plants was Philippus Aureolus Theophrastus Bombastus von Hohenheim. This Swiss citizen later adopted the Latin name Paracelsus and published the literary theory entitled Doctrine of Signatures. During the first half of the 16th century, Paracelsus traveled throughout Europe and to Asia and Egypt, curing people with his concoctions. He experimented with new plants in search of more treatment and solutions. As a professor of medicine at the University of Basel, in front of students he burned classical medical books by Theophrastus, Galen, Dioscorides, and Avicenna, but not Hippocrates.
The Doctrine of Signatures was highly developed during the European Renaissance. This interest paralleled the widespread belief in an overall unity of Nature.
Many vernacular names of temperate plants tell us how plants were once used to cure human ailments. Such uses were fueled by fertile imaginations. In general, long-lived plants were used to lengthen a personís life, and plants with rough stems and leaves were believed effective to heal diseases that destroy the smoothness of the skin. Plants with yellow sap were cures for jaundice, and roots with jointed appearance were the antidote for scorpion bites. Flowers shaped like a butterfly became cures for insect bites.