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|Māori names||raupō, koare, kārito, kōpūpūngāwha, kōpūngāwhā, ngāwhā. Numerous other names are used for various useful parts of the plant|
|Other common names||bullrush, raupō, cat’s-tail, cat’s-tail mace, broadleaf cumbungi|
|Scientific name||Typha orientalis|
The dry leaves are the traditional material used for covering poi, which are then filled with the fluffy down from the seed heads. The leaves are sometimes used to weave hats.
Traditionally, raupō stalks were used for thatching the walls and roofs of whare and storehouses, and the down was used to stuff bedding. The leaves were used for canoe sails and kites, while bundles of the stalks made temporary rafts. The starchy rhizomes were an important food, and the yellow pollen was gathered and baked into a sweet, light cake.
Raupō is a well-known and easily recognisable wetland plant. It grows up to 4 m tall, usually in large colonies, in shallow, fresh, or slightly brackish water. Erect, slightly fleshy, strap-shaped leaves up to 2 m long and about 2–3 cm wide are clustered on unbranched upright stems. Leaf bases have long sheaves, often 30 cm or more long, that encircle the stem.
Distinctive flower spikes borne near the top of stems provide a foolproof means of identification. Spikes are cylindrical clusters of tightly packed flowers encircling the stem, 2–5 cm in diameter and 10–30 cm long for female flowers, below and usually separated by a few centimetres from the much narrower and shorter cluster of male flowers. Copious quantities of mustard-yellow pollen are produced by the male spike in midsummer. The female spike develops tightly packed seeds with dense parachute hairs (pappus) facing outwards, to produce the distinctive velvety chocolate-brown seed head.
Distribution and ecology
Raupō inhabits shallow fertile waters, up to about 1.5 m deep, or water-logged soils in and around sheltered lakes, swamps, ponds or seepages, throughout most of the country, up to the lower montane altitudes. Raupō is absent from Stewart Island. It is also native to eastern Asia, from China and Japan southward to Australia. Although not threatened in New Zealand, its abundance has declined markedly due to the draining of about 80% of pre-European wetlands in the past 150 years.
Seedlings establish at the margins of waterways, or in mud during summer and autumn, and plants invade deeper water by growth of their rhizomes.
Water purification – a modern use
Rapid growth of raupō, stimulated by its fertile habitat and continual supply of moisture, results in annual biomass production that is among the highest of any habitat in the world. Rapid decomposition nearly balances this so that only about 6.5% ends up entering peat reserves in the wetland substrate. Dense productive stands enable raupō to be an effective purifier. Water flow is restricted allowing sediments to fall out of the water column, and the high demands of rapid growth absorb large quantities of nutrients and pollutants. Raupō roots also provide sites for microbes to attach to, which break down organic wastes and neutralise their toxicity. Along with other herbaceous aquatic species, raupō is being used in constructed wetlands, built specifically for water purification purposes. Stormwater, sewage, and effluent from mining sites and farm animals can be effectively treated this way. Where toxic residues build up, they can be dug out for further dryland treatment.
Raupō as a threat
Raupō tends to increase in abundance at the expense of other aquatic herbs in natural wetlands where there is high nutrient runoff from surrounding land. Plantings of raupō have the potential to become a weed problem but can be contained by trenches at least 2 m deep.
Natural and constructed raupō wetlands also provide valuable habitat for wildlife, including eels, water fowl, spawning whitebait (inanga) and other native fish, and including some uncommon or rare native birds such as fernbird, spotless and marsh crakes, and bittern.
Propagation is from seed and by division of mature root stock. Surface sow seed in a pot and stand in 3 cm of water. Pot up the young seedlings as soon as possible and, as the plants develop, increase the depth of water. Plant out in summer in a rich soil in boggy pond margins or shallow water to 15 cm deep. Divide mature rhizomes in spring, taking a young shoot with some root attached, and plant out into their permanent locations.