Urtica ferox, commonly known as tree nettle and, in Māori, ongaonga, taraonga, taraongaonga, оr okaoka, is a species of nettle endemic to New Zealand. Unlike the other species in the genus Urtica found in New Zealand, all of which are herbaceous, ongaonga is a large woody shrub that can grow to a height of 3 m (9.8 ft), with the base of the stem reaching 12 cm (4.7 in) in thickness. It has large spines that can result in a painful sting that lasts several days.

Urtica is a genus of flowering plants in the family Urticaceae. Many species have stinging hairs and may be called nettles or stinging nettles. The generic name Urtica derives from the Latin for 'sting'.