Urticaceae: The nettles plant family of the order Urticales, subclass Hamamelidae, class Magnoliopsida. Many have stinging hairs on stems and leaves. Flowers are small and greenish in leaf axils. The fruit is dry and one-seeded.Urtica dioica: A plant species of the genus Urtica, family URTICACEAE. Roots have been used to treat PROSTATIC HYPERPLASIA. Leaves are edible after the stinging quality is eliminated by brief heating.Pollen: The fertilizing element of plants that contains the male GAMETOPHYTES.