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.

The pale green leaves are very thin like a membrane and the surface of the leaf, stems and stalks are covered in stiff stinging hairs that can grow up to 6 mm (0.24 in) long.

Pollen grains are collected by the densely packed stigmas on the flowers and seed dispersal is carried out by rolling, wind, and by birds.

[7] The fruit, which are achenes, mature in January, each containing one 1.5 mm long, brown coloured, ovoid-shaped seed[8] which takes one month to germinate.

[13] U. ferox is endemic to New Zealand and inhabits coastal and lowland forests and shrublands in the North, South, and Stewart Islands.

[14] Although U. ferox is a toxic shrub, it also plays a significant part in the phenology of a native butterfly, namely the red admiral (Vanessa gonerilla).

The eggs of butterflies, also including the yellow admiral (Vanessa itea), are laid on the leaves of nettle during the spring and summer.

Beside these butterflies, some mammalian pests also eat the leaves of tree nettle, like the Common brushtail possum,[16] goats and deer.

This is significant as the species doesn't directly compete with other flora, this is achieved through inhabiting the boundary zones between strata, therefore the high soil fertility.

[medical citation needed] Māori used the bark of tree nettle and the leaves of kawakawa, boiled together, to make a liquid that can be used internally and externally for eczema and venereal disease.