Stinging praises

I appreciate one of my favourite plants at a distance (4 minute read)

A couple of days ago, I was walking in the hills above Wellington when I spotted one of my favourite plants. At first glance, it might seem an unlikely favourite, because it’s not the kind of plant you want to encounter on a dark night. In fact, I’d describe is as a plant best appreciated at a distance. Nonetheless, it's something special, and I'd like to share it with you.

Stinging nettles are found around the world, but only New Zealand has a giant tree nettle, also known as onga onga. The name is a slight exaggeration, because it usually grows only 2-3 metres tall. Still, that makes it a giant among nettles, because most don’t get over a metre. It also has giant spines. It’s hard to see the stinging spines on most nettles – if you are close enough to see the spines, you are probably already getting stung. Not so the tree nettle, whose leaves and stems bristle with fearsome spines.

That’s a lot of spines (image credit: Melanie Newfield)

Most nettle stings are an inconvenience – they sting for a while and are then forgotten. But stings from the tree nettle can cause more than a skin irritation. There is some evidence that the stings contain a nerve toxin, and both humans and other animals have sometimes suffered severe symptoms. There is at least one human death attributed to the tree nettle, as well as deaths of dogs and horses (other animals are not reported to be affected, according to Henry Connor’s book of The Poisonous Plants in New Zealand).

This doesn’t mean that you’re in danger of dying if you brush against a plant, not unless you’re allergic. Poisoning is a matter of dose, and it takes a lot of tree nettle stings to cause serious illness. Serious poisonings generally result from trying to walk through patches of it. Still, encounters can be painful, as I know from personal experience. I received a number of stings – through my clothing – when I was doing weed surveys in the Marlborough Sounds many years ago. On the worst occasion, I suffered more than a burning, red rash on my skin. I also had an awful headache for the rest of the day. It’s possible that the headache wasn’t connected to the nettle stings, but my commitment to science isn’t strong enough to tempt me into testing this by being stung again.

If it’s so unpleasant to encounter, why do I consider it one of my favourite plants?

Firstly, I love it when a New Zealander shines on the world stage. The tree nettle is one such New Zealander – it’s the world's largest, and most dangerous, nettle. Australia might have deadly spiders, snakes, jellyfish and all manner of other venomous animals, but they don’t have a deadly nettle. (They do, however, have a related tree, known as the gympie gympie, which is reported to have stings which are agonisingly painful, much worse than the tree nettle. The trans-Tasman rivalry even extends to our stinging plants.)

Secondly, I respect its assertiveness. On Friday, I wrote about the way fragmentation destroys the forest. Many of our native plants simply don’t survive in forest fragments. The tree nettle, however, grows naturally on edges and in gaps. In some places, including some of the Marlborough Sounds reserves where I worked, it guards the edges of fragmented forest. It’s a native plant which really stands up for itself, but it protects other plants as well. It helps to keep the forest interior cool and humid, as it is meant to be.

Thirdly, I admire its honesty. There’s nothing ambiguous about this plant. What you see is what you get. It looks dangerous, and it is dangerous.

There’s not much room for ambiguity with this plant (image credit: Melanie Newfield)

Finally, I love butterflies. When I see New Zealand’s red admiral butterfly, or kahukura – winner of the 2024 Bug of the Year competition – it delights me. But we wouldn’t have this beautiful butterfly if it wasn’t for the tree nettle. Although its caterpillars can feed on a few related species, the main host plant is the tree nettle.

The tree nettle doesn’t have bright flowers or a delightful fragrance. Even though I love it, if anyone told me they were planting it in their garden, I’d question their sanity. But it’s unique – it isn’t found anywhere except New Zealand. Other species depend on it. It has its place, and in its place, it’s perfect.

Image credit: Melanie Newfield