Nettle is a kind of perennial herb in Urticaceae. It originated in Europe, Asia, North Africa and North America and was introduced elsewhere. The species is divided into six subspecies, five of which have many hollow bristles called trichomes on leaves and stems, which act like hypodermic needles, histamines and other chemicals, and produce tingling when they are in contact ("contact urticaria"). This plant has a long history as a source of traditional medicine, food and tea.

Nettles are dioecious, perennial herbs that rise 1 to 2 m (3 to 7 ft) in summer and die on the ground in winter. It has widely spread rhizomes and stems, and its roots are bright yellow. Soft green leaves 3 to 15 cm (1 to 6 in.) long, opposite to erect, green stems. Leaves have a strongly serrated margin, a heart-shaped base and a acuminate tip, with the teeth at the end longer than the adjacent lateral branches. It has dense axillary inflorescences of small, green or brown flowers. The leaves and stems are very hairy, without stinging hair, and in most subspecies, there are many stinging hair (hairlike body or needle shape). When touching, its tip will fall off and become a needle, which can be injected with a variety of chemicals, causing pain, stinging or abnormal feeling, giving the species a common name: stinging nettle, nettle, weed or hazel tree.

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