URTICACEAE (nettle family), in botany, an order of Dicotyledons belonging to the series Urticiflorae, which includes also Ulmaceae (elm family), Moraceae (mulberry, fig, &c.) and Cannabinaceae (hemp and hop). It contains 41 genera, with about 500 species, mainly tropical, though several species such as the common 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 Parietaria (pellitory, q.v.).
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
opposite arrangement and are usually stipulate—exstipulate in
Parietaria. The position of the stipules varies in different genera;
thus in Urtica they are lateral and distinct from the leaf-stalk, in
other cases they are attached on the base of the leaf-stalk or stand
in the leaf-axil when they are more or less united. Stinging hairs
often occur on the stem and leaves (fig. 1). The bast-fibres of the
From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.
Fig. 1.—Stinging Hair of Urtica dioica, with a portion of the epidermis, and, to the right, a small bristle (⨉60).
Fig. 2.—Male Flower of the Nettle (Urtica). The four sepals are arranged symmetrically, an outer median and an inner lateral pair. A stamen is opposite each sepal, and in the centre of the flower is the rudiment of a pistil.
From Vines’s Students’ Text-Book of Botany, by permission of Swan Sonnenschein & Co.
Fig. 3.—A staminal (♂), B carpellary (♁) flower of the Nettle. p, perianth; a, Stamen; n′, rudimentary ovary of the ♁ flower; ap, outer, ip, inner, whorl of the perianth; n, stigma of the ♂ flower (enlarged). 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. The small inconspicuous regular flowers (figs. 3 and 4) are arranged in definite (cymose) inflorescence's often crowded into head-like clusters. 'They are uni sexual and monoecious or dioecious. The four or five green perianth leaves (or sepals) are free or more or less united; the male flowers (fig. 2) contain as many stamens, opposite the sepals, which bend inwards in the bud
Fig. 4.—Urtica urens (after Curtis, Flora Londinensis). 1, male flower; 2, female flower in fruiting stage-the dry compressed fruit 3 escaping from the persistent perianth; 4,fruit cut open, revealing the seed within the large straight embryo e. 1, 2, 3, enlarged. stage, but when mature spring backwards and outwards, the anther at the same time exploding and scattering the pollen. The flowers are thus 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 straight embryo is surrounded by a rich oily endosperm.