Urtica, from the Latin uro to burn, a name used by Horace and Pliny. Trees or shrubs with stinging hairs; leaves alternate, rarely opposite, simple, stipulate. Flowers unisexual with a single perianth whorl of 4-5 parts. Stamens with long filaments which uncoil elastically and violently. Fruit fleshy or non-fleshy, 1-seeded.