The concept behind the Doctrine of Signature first comes from the theory that God has marked everything that he created with a sign. This 'signature' was his indication of the reason why the living thing was created. The doctrine had been followed by apothecaries and herbalists for centuries.
The Doctrine states that, by observation, one can determine from the color of the flowers or roots, the shape of the leaves and roots, its habitat, or other 'signatures', what the plant's purpose was in God's plan. For example, Liverwort (Hepatica acutiloba), has a three-lobed leaf that supposedly bears a resemblance to the liver, and herbalists would prescribe this plant for liver ailments.
The shape, color, smell and the markings of certain plants were thought to indicate their usefulness in medicine. Pulmonaria has heart-shaped leaves spotted with silver, resembling a diseased lung, so was prescribed for consumption, and came to be called lungwort, or lung-plant. Red roses cured nosebleeds, as plants with a red signature were used for blood disorders. The petals of the iris were commonly used as a poultice for bruising because of the signature of color, the petals resembling a bruise. Plants with yellow flowers or roots, like goldenrod, were believed to cure conditions of jaundice because of its signature of color. All in all, we just need to pay attention.
It's hard to say when the Doctrine of Signature was first conceptualized. We all have a general understanding that many of the things that are/were discovered were discovered by way of Europe (cough…colonization). The Doctrine of Signature was observed and used across a multitude of cultures. It’s a staple in Traditional Chinese Medicine and Indian Ayurveda, as well as within Indigenous and African herbalism. Documentation says the Greeks were the first to publish the theory on the Doctrine of Signature, but publishing and discovering are not the same thing. Many Greek philosophers spent a good portion of their time studying in Egypt .Giordano Bruno, the great 16th-century champion of Copernicus, wrote,
''We Greeks own Egypt, the grand monarchy of letters and nobility, to be the parent of our fables, metaphors and doctrines.''
In the 17th century, a cobbler turned Christian mystic, Jakob Böhme, popularized the doctrine when he published a book-length thesis on it, “The Signature of All Things” (1621). In England, the herbalist and physician Nicholas Culpeper and the botanist William Cole wrote books of their own.
With modern medicine at the forefront, the Doctrine of Signature was viewed mostly as pseudoscience. The Signatures don’t take into account the dosage or toxicity of a plant, making it dangerous to rely solely on the theory. And of course a big majority of herbs have a multitude of uses, and not just those that correspond to their primary signatures. Horsetail has coarse, tail-like stalks resembling hair and while it might promote hair health, it’s also used for bone healing. The Doctrine of Signature is just one beautiful way that plants try to communicate with us!