Tree nettle facts for kids

Quick facts for kids Tree nettle
Urtica ferox leaves and spines
Scientific classification

Urtica ferox, often called the tree nettle or ongaonga (its Māori name), is a special plant found only in New Zealand. Unlike other nettles in New Zealand, which are small, soft plants, the ongaonga is a large, woody shrub. It can grow up to 3 m (9.8 ft) tall, with its base becoming 12 cm (4.7 in) thick. It has big, sharp spines that can give a very painful sting, which might last for several days.

The ongaonga plant is super important for the larvae (caterpillars) of the New Zealand red admiral butterfly, also known as kahukura. It's their main food source!

What Does the Tree Nettle Look Like?

This shrub can grow as tall as 3 m (9.8 ft) (about 10 feet), and its main stem can become 12 cm (4.7 in) (about 5 inches) thick. Its light green leaves are very thin, almost like paper. The leaves, stems, and stalks are covered in stiff, stinging hairs that can be up to 6 mm (0.24 in) long. These spines are easy to see along the middle vein and edges of the leaves.

The leaves are usually 3–5 cm (1.2–2.0 in) wide and 8–12 cm (3.1–4.7 in) long. They grow in pairs opposite each other on the stem. The leaves are shaped like an egg or triangle, with jagged edges, and each point has a spine. The spines on older, darker parts of the plant are smaller and softer, so they don't sting.

In cold places, this nettle loses its leaves in winter. In warmer areas, it stays green all year. It might also lose its leaves if the soil is dry and shallow.

How Tree Nettles Reproduce

Tree nettles flower from November to March. U. ferox is a dioecious plant, meaning it has separate male and female plants. This means they need to cross-pollinate, with wind carrying pollen from male flowers to female flowers.

After pollination, the fruit, called achenes, ripen in January. Each fruit holds one small, brown, egg-shaped seed, about 1.5 mm (0.059 in) long. These seeds take about a month to sprout. Even though not all seeds sprout right away, the plant can create a large "seed bank" in the soil. This means many seeds can stay in the ground for years, waiting for the right time to grow.

The Tree Nettle's Sting

The spines of the tree nettle contain a special toxin called triffydin. This toxin has chemicals like histamine, serotonin, and acetylcholine. Acetylcholine strongly affects your nervous system. Getting stung multiple times can cause a very painful reaction, including swelling, a rash, and itching.

In very serious cases, or with many stings, the toxin can cause more severe problems. It might lead to a loss of muscle control, low blood pressure, blurry vision, and confusion. There has been one sad case of a person dying after walking through a thick patch of ongaonga.

Where Tree Nettles Live

U. ferox is found only in New Zealand. It grows in forests and shrublands near the coast and in lower areas on the North, South, and Stewart Islands. You can often find it in open spaces or at the edges of forests, where it sometimes forms large patches. It grows from sea level up to 600 m (2,000 ft) high. It has also been seen growing along stream beds on the Hen and Chicken Islands.

Tree Nettle's Role in Nature

Even though U. ferox is a stinging plant, it's very important for a native butterfly: the New Zealand red admiral (Vanessa gonerilla). The leaves of the tree nettle are the favorite food for the butterfly's larvae (caterpillars). The leaves also provide a safe place for them.

When a caterpillar arrives on a nettle leaf, it curls the tip of the leaf and uses silk threads to stick the leaves together. This creates a secure little home where it can eat. Sometimes, the caterpillars eat so much that parts of the leaves fall off. The eggs of red admiral butterflies, and also the yellow admiral (Vanessa itea) butterflies, are laid on nettle leaves during spring and summer. The eggs hatch in about eight to ten days.

Besides butterflies, some mammals also eat tree nettle leaves. These include the Common brushtail possum, goats, and deer. However, before humans arrived in New Zealand, there were no land mammals that could fly or swim to the islands. So, the tree nettle didn't evolve to protect itself from these animals.

Tree nettles need lots of nutrients in the soil, like those found in healthy New Zealand forests. They grow well in soils rich in leaf litter and humus, especially those with high amounts of nitrogen. They also need plenty of sunlight and rainwater. This helps them grow quickly, especially in places where old trees have fallen, or after natural events like landslides or floods clear space.

Cultural Uses of Ongaonga

In Māori folklore, it's said that the great explorer Kupe used ongaonga as one of the obstacles to stop people who were chasing him.

The tree nettle has also been important for Māori as both a medicine and a food source. Māori people used the bark of the tree nettle and the leaves of kawakawa. They would boil them together to make a liquid that could be used on the skin or taken internally to help with eczema. The leaves were also used to treat pains. A liquid made from boiled leaves and young twigs was said to help with stomachaches.

It is also known that Urtica ferox was a food source for Māori. The inner stems were sometimes eaten after the leaves and outer bark were removed. The thin layer of inner bark was also eaten raw and was said to taste sweet. It is also recorded that stems were cooked after the leaves were taken off.

Images for kids

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  Urtica ferox leaves and spines

See also

In Spanish: Ongaonga para niños