Fantastically Wrong: The Strange History of Using Organ-Shaped Plants to Treat Disease

According to the doctrine of signatures, plants and nuts and vegetables that resemble a human body part or organ must be divined by God to treat said limb or organ. Thus should a walnut fix your brain if it gets too wrinkled … or something.

It’s hard to imagine being the first human being to look at a plant like, say, a stinging nettle and think, “I probably shouldn’t eat this, on account of the general agony it would cause me. But what if I cooked it first?” So you prepare it and nervously drop it down your gullet—and luckily enough, it turns out to be edible. But what if it hadn’t been? And what if there wasn’t a decent gastroenterologist nearby?

For tens of thousands of years before modern medicine, choosing plants that not only wouldn’t kill you, but could cure you of ills was an exercise in trial and error. So wouldn’t it be nice if nature (or God, who I guess would also be nature in a way) dropped hints as to which ones were good for the human body? Such thinking, known as the doctrine of signatures, actually developed with remarkable frequency all around the world from culture to culture. Plants meant to heal certain organs and body parts, like the liver or the eye, must show a certain “signature” by resembling the thing they treat.

So the bloodroot, with its red extract, was theorized to fix problems with blood. And the saxifrage, which breaks apart rocks as it grows, must relieve kidney stones. Venomous bites are covered too: Alkanet’s viper-shaped seeds help for snake bites, and the coiled shoots of the herb scorpius will take care of that scorpion sting lickety-split. Even using plants that grow in the same area where a disease like malaria is prevalent can be used as cures.

A 1923 reconstruction of an illustration from Giambattista Della Porta’s Phytognomonica of 1608. Eyebright, according to the doctrine of signatures, resembles the human eye and must therefore be effective at treating eye infections. But only if the eye is still in your head, not floating around disembodied like these ones.

We now know that this is both wildly wrong and wildly dangerous. A sliced mushroom may look like an ear, but that doesn’t mean you should eat it to cure your earache (choose the wrong mushroom and you can add 24 hours of talking to furniture to your troubles). But as we shall see, the doctrine of signatures, when properly applied, has in fact been for some cultures an indispensable tool in medicine.

Long before the theory popped up in the West, peoples all over the world subscribed to what we now call the doctrine of signatures, from Asia to the New World. Native American tribes all used it, according to Bradley C. Bennett in his essay “Doctrine of Signatures: An Explanation of Medicinal Plant Discovery or Dissemination of Knowledge?” The Cherokee, for instance, thought the common purslane’s stalks, which resemble worms, could be used to treat worms in humans.

In the West the doctrine was first mentioned in the writings of Pliny the Elder, the brilliant Roman naturalist whose imagination nevertheless often outpaced his grounding in reality. In the 1500s, German-Swiss physician Paracelsus wrote at length on the topic, claiming that “the soul does not perceive the external or internal physical construction of herbs and roots, but it intuitively perceives at once their Signatum.”

The 16th-century physician Paracelsus wrote extensively on the doctrine of signatures, apparently in a teeny-tiny notebook.

During the 16th and 17th centuries, the doctrine of signatures was ubiquitous in the West. According to Bennett, the view was a decidedly theological one: God, in all his/her benevolence, shapes certain plants to resemble human organs as a clue, and we need to take the hint. And if you don’t take the hint, well, God will force it on you. In Milton’s Paradise Lost, first published in 1667, the Archangel Michael uses the eyebright flower to cure Adam’s eye infection.

And there was the British botanist William Coles, writing a decade before that epic poem: “Though Sin and Satan have plunged mankinde into an Ocean of Infirmities, yet the Mercy of God, which is over all his workes, maketh Grasse to grow upon the Mountaines and Herbes for the use of men, and hath not only stamped upon them a distinct forme but also hath given them particular Signatures whereby a man may read the use of them.”

This theological grounding is quite problematic, in the sense that it assumes the universe was created for humankind, then stocked with convenient medicines for the taking, the kind of anthropocentric worldview also manifested in the geocentrism that Copernicus overthrew in the 16th century. There’s also the rather glaring issue of subjectivity: That root may look like a kidney to you, but it sure looks a lot like a liver to me.

Not that he needed to disprove the theory, but in his essay Bennett presents the findings of his research into the efficacy of various plants with heart-shaped leaves in treating heart disease. Searching various databases, he found 2,584 plants with such a shape, and randomly selected 80. Of those 80, only 21 were used in medicine, and of those only three applied specifically to cardiac medicine. “These data clearly refute any a priori value of heart-shaped leaves as signs for cardiac activity,” he writes. Translation: Don’t go around eating morning glory leaves to try to cure your heart murmurs.

The Archangel Michael, at left, was an early proponent of both sweet perms and the doctrine of signatures, using eyebright to restore Adam’s eyesight in Paradise Lost. Also, that kid is about to find out the hard way that pet fish don’t survive too good when walked on leashes.

And even in the heyday of the doctrine of signatures there were plenty of detractors. The 16th century Flemish physician Rembert Dodoens called it “absolutely unworthy of acceptance.” Even Samuel Hahnemann, who founded the practice of homeopathy, vehemently attacked the doctrine, which would turn out to be just as epically wrong as his own theory. He said in 1825 with an irony so hilarious it’s almost incomprehensible: “I shall spare the ordinary medical school the humiliation of reminding it of the folly of those ancient physicians who, determining the medicinal power of crude drugs from their signature, that is, from their color and form, gave the testicle-shaped Orchitis-root in order to restore manly vigour…”

Hahnemann and Dodoens were right, of course. But there is the problem of these supposed cures that … uh … actually work. The doctrine of signatures, it turns out, isn’t totally worthless bunk. The Cherokee’s worm-like purslane, writes Bennett, is indeed “effective in controlling intestinal parasite loads and has gastroprotective activity.” And the Archangel Michael’s eyebright, he adds, can be loaded into eye drops to treat infections of the peepers.

This orchid is good for those times when half of your penis falls off.

This could be coincidence, sure. But more likely it’s the fact that the doctrine of signatures has at times not been used to identify cures, but to remember them, and in that way has been quite beneficial for peoples without a written language. Where the vast majority of scholars have roundly dismissed the doctrine as silly pseudoscience, Bennett sees the mnemonic benefits of the theory. That is, its use as a device to memorize what plants can repair what problems in the human body.

He cites another scholar, writing in 2002 about the medicine of the native Peruvian peoples: “In these and other orally transmitted systems of thought, mnemonic cues may be essential to the viability of knowledge transmission. Plants that are both efficacious and easy to remember are more likely to be maintained in the pharmacopoeia of non-literate societies through time.”

In Europe, too, the doctrine of signatures was often applied after the plant’s efficacy had already been established. Bennett relates, for instance, the story of the discovery of willow bark’s powers. A reverend by the name of Edward Stone had accidentally tasted it, and found that its bitterness was much like that of cinchona bark, used to treat malaria. He then discovered that the willow could also be used to treat fevers, malarial or otherwise. And this, he concluded, is because the willow “delights in a moist and wet soil,” an environment where malaria is common. Cures, he reasoned, must occur near their causes.

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