The Doctrine of Signatures is an ancient belief that the appearance or “signature” of a plant shows what it can be used to treat in humans. According to this idea, God or nature gave plants certain shapes, colors, or markings as clues to their healing properties.
This concept was popular in ancient and medieval medicine, especially in Europe during the Renaissance. People believed that the way a plant looked indicated its medicinal purpose — for example, its color might suggest which part of the body it could heal.
Some classic examples include:
- Walnuts look like tiny brains, so they were believed to help treat brain disorders.
- Liverwort, which has liver-shaped leaves, was used to treat liver diseases.
- Bloodroot, with its red sap, was thought to help with blood-related problems.
- Eyebright, with flowers resembling an eye, was used for eye infections and vision problems.
The doctrine was first clearly described by Paracelsus, a Swiss physician and alchemist in the 16th century, and later expanded by herbalists like Jakob Boehme and William Coles.
Although modern science has shown that a plant’s shape or color does not actually determine its healing power, the Doctrine of Signatures played an important historical role. It encouraged early healers to observe plants closely, linking botany with medicine and paving the way for later scientific studies of medicinal plants.