If Looks Could Kill

Our forebears judged some plants by their looks to be medically beneficial, but the consequences of consuming certain species could be dire.

- Ian Morton

FOR many centuries, the theory held that, if some part of a plant resembled a human organ, then that plant could be used to treat the organ it resembled. At the heart of folk remedy and herbalism, this notion was nurtured throughout the Classical world by respected medical scribes, as far distant as Dioscorides and Pliny the Elder. It gained theological credence in medieval times and, for a while, was central to Western culture—it was known as the doctrine of signatures.

The 16th-century Swiss physician Paracelsus declared that ‘Nature marks each growth according to its curative benefit’ and German religious mystic Jacob Boehme travelled a similar course with Signature Rerum (The Signature of All Things, 1621), which is said to have influenced Newton and Nietzsche, among others. It resurfaced as recently as 2006, in the work of American author Elizabeth Gilbert, whose bestselling Eat, Pray, Love was made into a film in 2010.

For want of a better explanation, medieval medicine embraced the notion that the appearance of plants was a sign from the Almighty. Respected 17th-century English botanist William Coles wrote of herbs in Adam in Eden, or Nature’s Paradise, that ‘the Mercy of God... hath not only stamped upon them a distinct forme but hath also given them particular signatures whereby a man may read the use of them’.

Among his propositions was the claim that, because the bunched flesh inside the walnut resembled the human brain, it offered treatment for headaches. He also believed that, as holes in the leaves of St John’s wort (Hypericum perforatum) were rather like the pores in the human skin, the plant— also known as amber, amber touch-and-heal, demon chaser, goatweed and hardhay —was ‘profitable for all hurt and wounds that can happen thereunto’.