One of the most poisonous endemic plants, ongaonga or tree nettle (Urtica ferox), is an unwelcome garden plant, but integral to native ecology.
Fearsome of tooth, this stinging nettle exhibits narrow, sharply scalloped leaves and tender plant parts bearing pronounced white trichomes. These wicked needle-like projections contain a harmful toxin that causes acute pain and even nerve damage in humans and animals. Growing up to 3m in favorable conditions, tree nettle exhibits an open shrub-like habit, though appears as an herbaceous perennial when young and more isolated. "The ongaonga is said to begin life as a number of small plants, which spread (papa uku) over the ground, and are afterwards replaced by a single large stem" (Best, 1902). Its fruit and flowers are unremarkable.
Ongaonga grows in coastal-lowland forest margins and regenerating scrub on both islands. It performs best in fertile soils and open light, as is common in edge environments, and will not tolerate drought. In mild climates, it is evergreen, but grows increasingly deciduous with cold exposure. It is one of five native nettle species which grow in similar habitats, and even in wetland and montane environments.
Disdained for such malign touch, its critical role in the ecosystem is often disregarded. Ongaonga is a valuable insect refuge and food resource. Its leaves are the primary diet of the endemic red admiral butterfly, kahukura (Vanessa gonerilla) larvae, which knit themselves within its leaf tips for additional protection. Although this striking native is not at risk, habitat loss has removed all but a one wild population in Auckland.
Through spring and summer, it is also a host plant for native yellow admiral butterfly (Vanessa itea) eggs.
Though admiral butterfly larvae may feed from other native nettles, none are as hostile and defensive as U. ferox. Yet still, life finds a way (again). The shining cuckoo, pīpīwharauroa (Chrysococcyx lucidus), a migratory bird adapted to consume the uritcating body armour of toxic caterpillars, has recently been observed feeding on red admiral larvae directly from tree nettle shrubs, suggesting that it too has adapted to the plants' defenses.
Māori also traditionally ate the inner stems, which are said to be sweet, and boiled tre nettle's bark with kawakawa to treat skin conditions and venereal disease.
Best, E. (1902). Food products of Tuhoeland: being notes on the food-supplies of a non-agricultural tribe of the natives of New Zealand: together with some account of various customs, superstitions etc. pertaining to foods. . Transactions of the New Zealand Institute, (35): 45-111.