Mars, the Sting, and Urtication

Culpeper gives nettle to Mars, and the annotation attached to the pairing in this collection puts it correctly: the signature could hardly be plainer, since a plant that wounds on contact belongs to the planet of wounds and heat. Aries follows by rulership.

This is the doctrine of signatures functioning exactly as designed, and it is worth using it as a worked example of why the doctrine fails as pharmacology even where it looks convincing. The nettle's sting tells you the plant defends itself against grazing. It tells you nothing whatever about what the plant does when eaten, and in fact the plant when eaten is a mild nutritious vegetable with no martial properties at all. The signature and the action point in opposite directions. That the reasoning feels compelling is a fact about human pattern-matching, not about nettles.

The one traditional practice where the sting itself is the treatment is urtication: deliberately whipping rheumatic, arthritic or paralysed limbs with fresh nettles. This is documented from the classical period through to the nineteenth century and survives in folk use. The effect is counter-irritation, a strong superficial stimulus producing local hyperaemia and temporarily masking deeper pain, which is a real if crude physiological phenomenon and the same principle as mustard plasters and liniments. It is a rare case of a plant used for the property the signature actually indicates.

Culpeper also records nettle as a blood-cleanser and diuretic. Nettle is indeed diuretic, and modern herbal use continues on that basis.