Updated: May 16, 2019
In the 1500s, a medical theory that we call The Doctrine of Signatures became popular, first in Italy, and then throughout Europe. Based on the concept that God gave each plant a physical signature that would indicate its healing power, this theory was fascinating, in that it was sometimes right. The idea that a plant’s mere appearance could tell its use continues well into modern day herbalist schools of thought.
We see this most often with plants that resemble parts of the body. Some of the most famous examples are walnuts for brain health, tomatoes for heart health and Lungwort for lung issues. Plants that grew in certain areas told a different story. Those that grew in groups were considered milder in strength than those that grew alone. (Yarrow would be considered a stronger plant than clover.) Plants that grew near populations were thought to be safer to use for long periods of time (Dandelion) than those that grew out in the woods (Blue Cohosh). Healing women of the time would also use this theory to explain why certain plants found growing around the houses of patients would be the very plant that the patient needed to heal his or her ailment.
Of course, not every plant can be categorized based on its appearance alone. A true natural study of plant properties considers a holistic approach, including the history of use, appearance, growth patterns and most importantly, scientific studies.
Unfortunately, the blind belief in The Doctrine of Signatures eventually caused many poisonings and deaths. This is why it’s not always safe to assume that an English name for a plant is an indication of what it treats.