Characters.—Flowers herbaceous, inconspicuous, polygamous. Calyx membranous, lobed, persistent. Stamens definite, distinct, inserted in the base of the calyx, and opposite its lobes. Ovary superior, simple. Ovule solitary, erect. Fruit a simple, indehiscent nut, naked or surrounded by the persistent calyx. Embryo straight, with fleshy albumen; cotyledons flat; radicle superior—Trees, shrubs, or herbs. Leaves frequently covered with asperities or stinging hairs. Stipules mostly persistent, rarely deciduous or absent.
Properties.—The order is now very circumscribed; and contains but few properties interesting to the physician. The most remarkable properly of the order is the acridity (sometimes very extreme) of the liquid contained in the epidermoid gland at the base of the stinging hair. Endlicher [Enchiridion Botanicon.] says that it is bicarbonate of ammonia; but this is an obvious error, as ammonia, in any known form, is incompetent to produce the violent effect ascribed to some of the East Indian Urticaceae.
Urtication, or flagellation by a bunch of nettles (Urtica dioica), is an old method of treating palsy. [Celsus, lib. iii. cap. 27.]