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November - Ongaonga - Native Plant of the Month


Urtica ferox

If a punk was ever transformed into a plant, they would almost certainly look a lot like an ongaonga, or tree nettle. Even if you have never seen a nettle before, it would be hard to imagine that this plant would be nice to touch - it is so obviously covered in huge needle-like spines. Even the tiny flowers are nestled amongst spiky protection. Ongaonga are only found here in Aotearoa and grow in the ngahere throughout the country, especially in clearings and bush edges. They are the biggest nettle in the world and can reach 3-4m tall. Ongaonga are also considered the world’s most dangerous stinging plant. Every part of them, apart from their roots, is covered in large, pale spines. This is a plant that manages to bite back, which is quite incredible for an organism that is rooted to the spot. If a person, or animal, brushes against ongaonga the fine tips of the spines break off and the skin is injected with a painful cocktail of chemicals that cause a strong histamine response. Small stings cause acute pain, tingling and numbness that can last days. Greater exposure can cause nervous damage, blindness, paralysis and death. At least two human deaths have been caused by ongaonga stings as well as several dogs and horses. While it is sometimes a kiwi point of pride to say that unlike the Aussies the only real danger in our bush is exposure, it is sensible to remember that the ongaonga are out there too.

Ongaonga with caterpillar on underside of leaf stem.

But just like many punks, ongaonga have a softer side too and are very worthy of our love (or at least awe). Our native plants have important relationships with our native animals and ongaonga are no exception. They are an important food for the caterpillars of our endemic red admiral butterflies - also known as kahukura. The caterpillars sew ongaonga leaves up with silk to make a protective shelter that is extremely predator-proof. Kahukura populations seem to be declining and one reason for this is the loss of host plants. Astonishingly, one of the natural predators of kahukura caterpillars - shining cuckoos, appear to have developed a resistance to ongaonga spines. This means that they are able to hunt for the caterpillars among the spiny leaves without any harm. You can read about this and see some great photos of shining cuckoos hunting in ongaonga in this Te Papa blog post. Interestingly, there are anecdotal accounts that possums, deer and goats also seem undeterred by ongaonga’s venomous spines and will readily eat and destroy ongaonga plants.

Red admiral / Kahukura

In the Northern hemisphere nettles are often eaten as a nutritious food. Māori too worked out how to get past ongaonga’s defensive spines to eat the inner bark of the stems, which apparently taste sweet. Māori have worked out other uses for ongaonga as well, including planting it around fortified areas on Pā to deter intruders and using leaves and stems to make a treatment for eczema. Interestingly, despite its ability to cause huge pain, ongaonga is being investigated as a potential treatment for chronic pain conditions such as diabetic neuropathy.

If you still aren’t too keen on seeing this unusual plant, you may be comforted by the fact that there isn’t too much ongaonga around Auckland, and we know of none growing in Kaipātiki. iNaturalist shows just three ongaonga sites in Auckland and only one of these is in the wild. Because of the need to stay on track to protect our kauri you are not likely to accidentally blunder into one in Auckland (or Northland for that matter). If you do want to see one of these infamous plants in the flesh, there is a very well fenced and signed specimen growing in Ambury Park.

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