URTICACEAE (nettle family), in botany, a family of flow ering plants belonging to the order Urticales, which includes also Ulmaceae (elm family), Moraceae (mulberry, fig, etc.) and Can nabaceae (hemp and hop). It contains 41 genera, with about 48o species, mainly tropical, though several species such as the com mon stinging nettle (Urtica dioica) are widely distributed and occur in large numbers in temperate climates. Two genera are represented in the British Isles, Urtica (see NETTLE) and Parie taria (pellitory, q.v.). In addition to Urtica and Parietaria, four other genera,—Boehmeria, Hesperocnide, Laportea and Pilea, are represented in North America, with some 15 native species.
The plants are generally herbs or somewhat shrubby, rarely, as in some tropical genera, forming a bush or tree. The simple, often serrated, leaves have sometimes an alternate sometimes an oppo site arrangement and are usually stipulate—exstipulate in Parie taria. Stinging hairs often occur on the stem and leaves. The bast-fibres of the stem are generally long and firmly attached end to end, and hence of great value for textile use. Thus in ramie
(q.v., Boehmeria nivea) a single fibre may reach nearly 9 in. in length, and in stinging nettle as much as 3 in. Maoutia and Urtica have also been used as sources of fibre. The small incon spicuous regular flowers are ar ranged in definite (cymose) in florescences often crowded into head-like clusters. They are uni sexual and monoecious or dioe cious. The four or five green perianth leaves (or sepals) are free or more or less united; the male flowers contain as many sta mens, opposite the sepals. The flowers are adapted for wind pollination. The female flower contains one carpel bearing one style with a brush-like stigma and containing a single erect ovule. The fruit is dry and one-seeded; it is often enclosed within the persistent perianth. The family is divided, according to Engler, into two main classes : (I) the Urereae with stinging hairs, includ ing the genera Urtica, Urera, Laportea, and ( 2 ) others, which are without stinging hairs.