Urtica dioica

Urtica dioica, often known as common nettle, burn nettle, stinging nettle (although not all plants of this species sting) or nettle leaf, or just a nettle or stinger, is a herbaceous perennial flowering plant in the family Urticaceae. Originally native to Europe, much of temperate Asia and western North Africa, it is now found worldwide. The species is divided into six subspecies, five of which have many hollow stinging hairs called trichomes on the leaves and stems, which act like hypodermic needles, injecting histamine and other chemicals that produce a stinging sensation upon contact ("contact urticaria", a form of contact dermatitis). The plant has a long history of use as a source for traditional medicine, food, tea, and textile raw material in ancient (such as Saxon) and modern societies. Urtica dioica is a dioecious, herbaceous, perennial plant, tall in the summer and dying down to the ground in winter. It has widely spreading rhizomes and stolons, which are bright yellow, as are the roots. The soft, green leaves are long and are borne oppositely on an erect, wiry, green stem. The leaves have a strongly serrated margin, a cordate base, and an acuminate tip with a terminal leaf tooth longer than adjacent laterals. It bears small, greenish or brownish, numerous flowers in dense axillary inflorescences. The leaves and stems are very hairy with non-stinging hairs, and in most subspecies, also bear many stinging hairs (trichomes or spicules), whose tips come off when touched, transforming the hair into a needle that can inject several chemicals causing a painful sting or paresthesia, giving the species its common names: stinging nettle, burn-nettle, burn-weed, or burn-hazel. Credit for the scientific naming of Urtica dioica is given to Carl Linnaeus who published it in Species Plantarum in 1753. The taxonomy of Urtica species is confused, and sources are likely to use a variety of systematic names for these plants. Until 2014 there was broad consensus that the nettles native to the Americas, now classified as Urtica gracilis, were subspecies of Urtica dioica.