Doctrine of signatures

The doctrine of signatures, dating from the time of Dioscorides and Galen, states that herbs resembling various parts of the body can be used by herbalists to treat ailments of those body parts. A theological justification, as stated by botanists such as William Coles, was that God would have wanted to show men what plants would be useful for.

Today considered pseudoscience,^{[1][better source needed]} the practice has historically led to many deaths and severe illnesses. For instance, birthwort (so-called because of its resemblance to the uterus) was once used widely for pregnancies, but is carcinogenic and very damaging to the kidneys, owing to its aristolochic acid content.^[2] As a defense against predation, many plants contain toxic chemicals, the action of which is not immediately apparent, or easily tied to the plant rather than other factors.