a plant of the genus urtica, covered with minute sharp hairs containing a poison that produces a stinging sensation. urtica gracitis is common in the northern, and u. chamaedryoides in the southern, united states. the common european species, u. urens and u. dioica, are also found in the eastern united states. u. pilulifera is the roman nettle of england.-to fret or sting; to irritate or vex; to cause to experience sensations of displeasure or uneasiness not amounting to violent anger.