Parataniwha

Botanical name: Elatostema rugosum
Synonyms: None
Common name(s): Parataniwha, Paratāniwhaniwha, New Zealand Begonia, Begonia Fern

About:
Parataniwha is a lush, spreading forest herb and New Zealand’s only native species of Elatostema. It forms large colonies of fleshy stems and broad, strongly wrinkled leaves in damp, deeply shaded places.

Although it belongs to the nettle family, it has no stinging hairs. Its colourful foliage may be green, bronze, purple or reddish, especially on young growth, and gives the plant a distinctly tropical appearance.

Natural habitat:
Occurs in damp, shaded places in lowland to montane forest. It is especially common beside streams, rivers, waterfalls and wet rock faces, and in gullies where humidity remains high throughout the year.

Plants often form extensive mats on moist banks, rocky stream margins and forest floors. Their stems may trail across the ground, root at the nodes and cascade over damp cliffs.

Growing environment:
Requires full shade or deep filtered light, consistently moist soil and protection from drying winds. It performs best in cool, humid conditions with rich organic soil and reliable summer moisture.

Parataniwha tolerates cool climates but is vulnerable to severe frost, especially when grown without overhead shelter. It does not tolerate prolonged drought or exposed sunny positions.

Endemic distribution:
Endemic to New Zealand and naturally confined to the North Island. It occurs from North Cape south to Kapiti Island and the Tararua Range.

It is most common in northern and central districts and becomes locally sparse in the lower North Island.

Height:
Usually 30–80 cm, occasionally reaching approximately 1–1.5 m

Width:
Spreads indefinitely by rooting stems, often forming colonies several metres across

Flowering:
Mainly spring to autumn, generally September–May

Fruiting:
Spring to autumn, often overlapping with flowering

Uses:
• Shaded native groundcover
• Streamside and gully planting
• Damp woodland gardens
• Fernery and subtropical-style planting
• Erosion reduction on moist banks
• Cultural and educational planting
• Habitat for small forest invertebrates

Appearance:
Growth habit:
A perennial herb with stout, succulent stems that are woody near the base. Stems initially spread along the ground, then rise upright or arch outward.

The plant roots where stems contact moist soil, allowing it to form broad, dense colonies.

Stems:
Stems are fleshy, juicy and sparsely branched. The lower portions may become woody with age, while the upper growth remains soft and flexible.

The tips often bend or arch toward the light.

Leaves:
Leaves are alternate and arranged largely in a single plane along the stem. They are approximately 8–25 cm long and 2.5–6 cm wide.

Each leaf is noticeably asymmetrical, with one side of the blade broader than the other. The blade is oblong, lance-shaped or obovate-oblong and has sharply toothed margins.

The surface is strongly wrinkled or puckered, reflecting the meaning of the name rugosum. Leaves may be green, dark green, bronze, purple or reddish, with young leaves often showing the strongest red coloration.

Leaves are nearly stalkless, with bases that partly clasp the stem. Dark veins are often conspicuous against the blade.

Flowers:
Flowers are extremely small and grouped into dense rounded clusters at the bases of the leaves. These clusters may reach approximately 1.5–2 cm across and are partly enclosed by papery bracts.

Male and female flowers may occur on separate plants, although mixed clusters are sometimes present. Male flowers are more numerous and borne on tiny stalks, while female flowers are mostly stalkless and have tufted stigmas.

The projecting stamens of the male flowers release pollen suddenly, contributing to the genus name Elatostema.

Fruit:
The fruit is a minute, papery achene, generally less than 1 mm long. It is smooth, pale brown and elliptic to egg-shaped, with a pointed tip.

Seeds:
Seeds are extremely small and dark coloured. The fruits are dispersed by explosive projection and by flowing water.

Ecology:
Parataniwha is strongly associated with cool, continuously moist forest environments and can indicate sites where soil moisture and humidity remain high.

Its dense foliage shades the ground, retains moisture and creates shelter for small invertebrates. Where leaves overhang streams, they may contribute to small aquatic and stream-edge microhabitats.

The plant supports several native insects, including moth larvae and scale insects. Slugs and snails may also feed on the soft foliage.

Its red and bronze juvenile leaves contain high levels of anthocyanins, pigments that may help protect young tissues from light stress and cellular damage.

Associated habitats:
Shaded stream margins, riverbanks, waterfall spray zones, wet gullies, damp cliffs, rocky forest floors and moist lowland to montane forest.

Associated species may include tree ferns, filmy ferns, mosses, liverworts, kiekie, supplejack, hangehange, kawakawa and other moisture-loving forest herbs.

How to grow:
Plant in full shade or deep filtered light in rich, moisture-retentive soil. Add composted leaf mould or fine organic material and apply mulch to keep the root zone cool.

Water regularly during dry weather and never allow the soil to dry out completely. A sheltered position beneath trees, beside a pond or in a damp fernery is ideal.

Protect from hard frost, hot afternoon sun and drying wind. In colder districts, grow beneath an established canopy or against a sheltered south- or east-facing wall.

Plants spread readily once established and may need occasional trimming to keep them within the desired area.

Propagation:
Propagation is easy by division or stem cuttings. Lift rooted sections of trailing stem and replant them directly into moist, shaded soil.

Cuttings can be taken from healthy fleshy stems and inserted into a humid propagation medium. Keep them shaded and continuously moist until rooted.

Seed may also be used, but the seed is minute and more difficult to handle. It should be surface-sown on moist medium and kept cool and humid.

Cultural use:
Parataniwha leaves were traditionally used by Māori when cooking kūmara in a hāngī, where they helped wrap the food and were said to contribute flavour.

The name parataniwha has been interpreted as referring to a place or home associated with taniwha, reflecting the plant’s connection with damp, shaded waterways and secluded forest gullies.

The botanical name Elatostema refers to the projecting or explosively moving stamens. The specific name rugosum means wrinkled and describes the deeply puckered leaf surface.

Garden value:
Parataniwha is one of New Zealand’s finest native foliage plants for deep shade. Its large textured leaves, rich bronze and purple tones and dense spreading habit provide a lush ground layer beneath trees and around waterways.

It is particularly valuable for ferneries, shaded courtyards, streamside gardens and moist native plantings where few other groundcovers perform as well.