Hand-colored scanning electron micrograph of the stinging nettle hair (Urtica dioica), by Martin Oeggerli.
The Stinging Nettle (Urtica dioica) is a plant with soft green leafs that are equipped with glands as well as short non-stinging and special elongated stinging hairs (center), from which the species derives its common names: stinging nettle, burn nettle, burn weed, or burn hazel.
Stinging hairs (trichomes) produce a painful stinging sensation by injecting a chemical mixture when touched by humans or other animals. They act like hypodermic needles: after the tip breaks off, a chemical mixture composed of histamine, acetylcholine, 5-HT (serotonin), moroidin, leukotrienes and formic acid is injected and causes pain or paresthesia.
Furthermore, the plant has a long history of use in medicine, as food source (tea) and as source of fibre.