¡Ongaonga!

Urtica ferox- The Tree Nettle

Urtica ferox in Dunedin Botanic Garden

Though generally a safe and hospitable land in terms of predators and poisonous beasties, New Zealand is not entirely devoid of floral hazards that can pack a punch. Case in point- Urtica ferox, the native Tree Nettle or Onganonga. In the same genus as the UK’s own stinging nettle (Urtica dioica), Ongaonga is New Zealand’s very own supercharged endemic equivalent. It is easily distinguished from other members of its genus as its growth habit is that of a woody shrub rather than a herb.  The plant is widely distributed across both the North and South Islands of New Zealand and can mainly be found growing in areas of temperate bushland. Thickets of Ongaonga are not unknown and usually occur in areas of sloped debris. An incredibly hardy plant, Ongaonga is able to withstand temperatures as low as -8⁰C.

Tree Nettle is dioecious, meaning that male and female flowers occur on separate specimens of the plant. Small green flowers borne on spikes up to 8cm in length grow from the leaf axis of the plant between the months of November and March. Pollen from the male flowers is then dispersed by the wind to their female counterparts, which following successful pollination, develop into small, brown nut like fruits of one and half millimetres in length.

Leaves of the mighty Ongaonga

Perhaps the defining feature of the Ongaonga in terms of human interaction with the plant is its incredibly powerful and irritable sting. Stiff, hypodermic needle-like  hairs adorn the plant’s flowers and branches as well as the veins, stalks and edges of the deeply jagged leaves. Each hair is around 6mm in length. When touched the hairs break and release a potent mixture of intoxicants that can result in a host of painful and in very rare cases, deadly reactions. Though rare, there have been accounts of dogs, horses and even one very unfortunate walker meeting their maker at the hands of the Ongaonga’s sting. Fortunately for the rest of us, a brush with the Ongaonga will generally not result in death but rather a great deal of incredible discomfort lasting somewhere in the region of three days. Indeed, the variety and intensity of the symptoms brought on by the Ongaonga’s sting are quite remarkable (see table below).

Yowza!

Possible symptoms following contact with Tree Nettle

Time after contact	Symptoms
Immediately	Painful, burning sensation Numbness
15-20 minutes	Abdominal cramps Strong burning sensation in feet Visual blurring
60–90 minutes	Weakness, exhaustion Confusion  Pale skin Sweating Salivating  Cramps Breathing problems Loss of eye sight (!) Problems regulating body temperature Problems controlling movement of arms and legs

However, the Ongaonga’s lack of hospitality for the human race does not extend to all creatures. The Tree Nettle plays a vital ecological role in the life cycle of the Red Admiral Butterfly (Vanessa gonerilla), another species endemic to New Zealand. The butterfly lays its eggs amongst the spines of the Ongaonga’s leaves, which are the main food source of the Red Admiral Caterpillar. The caterpillar also uses the plant as protection from predators by folding the leaves around their bodies effectively creating a makeshift tent. Fantastic!

 

Red Admiral Caterpillar in a tent

Though eradicating the Tree Nettle would undoubtedly remove a potentially harmful element from our environment, the ecological implications for other inhabitants of our planet would be massive. Ongaonga is not just a plant, it is a home and nourishment for other species. Remember this if you are ever stung and your arms and legs start flailing wildy, your vision blurs and your body temperature begins to fluctuate. It may seem like a good idea to go back and exact horticultural vengeance but be mindful folks and look at the bigger picture.