The doctrine of signatures is the old idea that a plant shows you what it is for. A lobed leaf for the liver. A spotted leaf for spotted lungs. People bring it up to explain how the old timers knew which plants to use, and that is where it has things backwards. Nobody found these plants by looking at them. They found them by eating them, by watching sick animals, by seeing what happened to the people who tried them, and by paying attention for a very long time. The likeness got noticed afterward, and then it did a useful job. It gave people a way to remember.
How Anyone Knew in the First Place
Four things did the work.
They watched animals. Sick animals eat what they do not normally eat, and anybody living close to animals notices. Go through folk traditions around the world and you find a long list of remedies where the people using them say they got it from watching an animal. Chimpanzees chew a bitter pith to clear worms, and people in the same part of Africa use that plant the same way. When William Coles wrote in 1657 that the farmers of Kent gave mullein to their cattle for a cough, he was watching it run the other direction.
They tasted. Chew a leaf and you learn something. Bitter is one kind of plant. Slick and coating is another. A pucker that dries your mouth out is a third. That does not tell you what a plant will do in a person, but it sorts plants into families that behave alike, and it takes four seconds and no equipment. So the old timers were reading signs. They were reading them with their mouths instead of their eyes.
They saw how people fared. Somebody takes a thing and then gets better, or does not, and everybody in the house sees which. That is the test the other three answer to. It is slow and rough, and it is still the only one of the four that tells you whether the plant did anything at all.
They had time. Not a laboratory's kind of trial and error. Whole villages, every day, for hundreds of years, remembering what hurt somebody as carefully as what helped. The old poison lore is as detailed as the old medicine lore, and that tells you people were paying attention rather than guessing.
It was still being lived inside living memory. Researchers who sat down with 660 older people across the southern mountains found that into the 1920s and 1930s the bulk of the home medicine chest was plant food, the things families grew and ate. Most of that is gone now. Nobody wrote it down because nobody thought it needed writing down.
So What Was the Doctrine For
Think about handing something on before books were cheap. You learn that a leaf eases a cough, and you have to pass it to somebody who cannot read, without writing it down, and have it outlive you. A likeness gives you a handle. The leaf that looks like a lung, for the chest. That sticks.
That is a real job and we are not going to talk down about it. It is not the same as evidence. A likeness helps the knowledge travel, but it cannot find the knowledge and it cannot check it.
Who Wrote It Down
Paracelsus, who died in 1541, said nature marks every plant according to what it is good for. Giambattista della Porta built it out in a book in 1588 and Jakob Bohme gave it its name in 1621. William Coles said it best in the 1650s, that God gave herbs signatures whereby a man may read the use.
Doctrine of Signatures Examples
These are the matches those writers handed down, and they are the ones still passed around today.
- Lungwort for the chest, read off the pale spots on its leaves.
- Liverwort for the liver, because the leaf is lobed like one.
- Walnut for the head. The shell opens like a skull and the kernel inside is folded like a brain.
- Eyebright for the eyes, off a small dark mark in the flower.
- Birthwort for childbirth, from a flower somebody read as a womb.
Read as a list it is convincing.
Is the Doctrine of Signatures True?
No. Read as a method it falls apart the moment you ask how many plants have a leaf that could pass for something. Almost any plant can be made to look like almost any organ if you want it to, and nothing on the outside of a plant connects to what is inside it. The likenesses are real, they are just not reasons, and every time we go looking at the order of events we find the plant already in use and the likeness noticed later.
Mullein Was Called Lungwort, and Not For the Reason You Would Guess
We wildcraft mullein in south Alabama and cut every leaf by hand, so this one matters to us more than the rest.
Mullein is the plant people hand to the doctrine now. The leaf is thick and pale and woolly, the veining branches the way airways branch, and once somebody sets it beside a picture of a lung you cannot unsee it. The plant even carries the name. Old country names for it are Clown's Lungwort and Bullock's Lungwort.
Go back to the record, though, and the resemblance is not there. Grieve's A Modern Herbal explains mullein's long run in chest complaints by what the leaf does, soothing and coating, and never once reaches for how it looks. What it does have is Coles in 1657 on the farmers of Kent and their cattle. The man who wrote that God signed the herbs gets to mullein and writes down what farmers did with their cows.
Notice what soothing and coating means in the mouth, too. It is the slick feel off a chewed leaf, inside of a few seconds. Anybody can read that sign, and it has nothing to do with how the plant looks.
Real Lungwort, the Pulmonaria, was named the other way round, off the spots. Mullein borrowed the word because of what it was used for. Two names that look like the same story, and only one of them is a signature. None of this tells you what mullein does in a person, and our mullein page covers the plant itself.
The Newest Signature Is Four Hundred Years Too Late
Somebody set a photograph of a sweet gum ball beside a drawing of a virus, and it is hard to shake off. The pod is a ball covered in spikes. The drawing is a ball covered in spikes.
The doctrine cannot hold that one. Paracelsus died in 1541 and Coles wrote in the 1650s, and nobody saw a virus until the twentieth century. You cannot read a pod as the sign of a thing nobody knows is there. The resemblance is real, the lineage is invented, and it was invented in the last few years by whoever made that picture.
What we know about those pods has nothing to do with their shape. The infertile seeds inside carry shikimic acid at up to 6.5 percent by dry weight, against 0.14 percent in the fertile seeds of the same pod (Enrich et al., 2008, Tetrahedron Letters). What that does and does not mean is on our sweet gum page, where it has been since we wrote it.
Where This Goes Wrong
Birthwort is the reason to take it seriously. It was read as a womb and given to women in labor for centuries on the strength of that shape. It contains aristolochic acid, which scars the kidneys and causes cancers of the urinary tract. The resemblance was good and the plant was dangerous.
Every other way of knowing has a check built into it. An animal that eats the wrong thing dies and the people watching learn it. A taste that warns you is something you can act on. Watching how somebody fared afterward tells you plainly whether you were right. Generations of use catch what one generation misses. A likeness has no check in it at all, which is how it can run four hundred years without ever correcting itself.
How We Decide What to Say About a Plant
A resemblance is a story, and we will tell a good story. Traditional use is history, so we say who used a plant and when. Where there is laboratory work we name the study and the year and then stop. None of those is a claim about what a bottle will do for you.
If a page tells you a plant cures something because of how it looks, you have learned something about the page.
Frequently Asked Questions
What is the doctrine of signatures?
The idea, written down in Europe in the 1500s and 1600s, that a plant's shape or color or taste shows what it should be used for. It ran through medical writing for about three hundred years and is no longer part of medicine.
How did people know which plants were medicine before any of it was written down?
By eating plants across seasons, by watching what sick animals went looking for, by tasting, and by handing down what worked while remembering what did harm. None of that is fast and none of it is guessing.
Did people really learn about plants from animals?
There is good evidence for it. Researchers going through folk traditions keep finding remedies the people using them credit to watching an animal, and chimpanzees chew a bitter pith for intestinal worms that people in the same region use the same way.
Who came up with the doctrine of signatures?
Paracelsus, who died in 1541, gave it its clearest early statement, and Giambattista della Porta and Jakob Bohme developed it over the next eighty years. William Coles put it most memorably in the 1650s, writing that God gave herbs signatures whereby a man may read the use.
Is the doctrine of signatures true?
No. The likenesses are real but they carry no information, and the record suggests the likeness was usually noticed after a plant was already in use rather than being what led anybody to it.
If signatures did not lead anyone to these plants, what were they for?
Remembering. Plant knowledge had to move between people who could not read, without notes, over long stretches of time, and a likeness gives it a handle.
Does mullein look like a lung?
A lot of people think so, and the veining does branch the way airways branch. What the record does not show is anybody using mullein because of that, and Grieve's A Modern Herbal explains its use in chest complaints by the way the leaf soothes and coats.
Are mullein and lungwort the same plant?
No. Real lungwort is Pulmonaria, which got its name from the pale spots on its leaves. Mullein picked up the country names Clown's Lungwort and Bullock's Lungwort from what people used it for. The word is shared, the reason behind it is not, and the two plants are not related.
Do sweet gum balls look like a virus?
The spiky pod does resemble the usual drawing of one, and that is a coincidence rather than a signature. The doctrine was written in the 1500s and 1600s and viruses were not known until the twentieth century, so no old tradition could have made that connection.
Keep Reading
- Mullein leaf. The plant we wildcraft in south Alabama and cut by hand.
- The sweet gum tree. Green seed balls, and what is inside them.
- Shikimic acid. What it is and what it is not.
- The moringa we grow. Our oldest planting, in the ground since 2015.
- Back to the Learning Center
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