In The Hills In The Hills 2016-08

Blechnum filiforme < Species index > Blechnum novae-zelandiae

This article was first published in the Tararua Tramper Volume 88, no 3, April 2016

August in the hills with Chris Horne and Barbara Mitcalfe

Blechnum fluviatile, kiwakiwa, ray water fern

Look for kiwakiwa when you are tramping - it is a distinctive ground fern, common throughout New Zealand, in lowland to montane forests, usually in damp, shaded areas, often beside waterways. Like all members of the Blechnum genus, its sterile fronds and fertile fronds are very different from each other. ‘Blechnum’ was the Greek name of a particular fern, and ‘fluviatile’, derived from Latin, means associated with rivers.

Form

Kiwakiwa: upright, fertile fronds and spreading, infertile fronds Photo: JEREMY ROLFE

Kiwakiwa‘s mature sterile fronds arise from the centre of a dense, flat, rosette of juvenile fronds. When mature, they are 15-75 cm long x 2-6 cm wide, with 20-60 pairs of crowded, rounded, dark-green segments, all about 10-30 x 8-12 mm. The stalks and rachises (the part of the frond bearing the segments) are covered in dark-brown scales. The fertile fronds are upright, arise from the centre of the plant, and are similar in length, or slightly longer, than the sterile fronds.

Reproduction

The sori, which contain the spores, develop on one side of each fertile frond. At first the sori are green, but as they ripen, they turn brown and release their spores, which can be carried a considerable distance by the wind. When a sorus (singular of sori) lands, it forms a prothallus, and if the conditions are right, i.e., moist and shaded, it will develop into a young kiwakiwa. (See our article on the complete fern life-cycle in the December 2015 article).

Uses

A rāhui is a sign, or a symbol, to warn people that something in the immediate vicinity, e.g. a crop of ripening kūmara, should not be approached, except by certain authorised people. To warn of the presence of a rāhui, a tohunga would choose a site in the vicinity for a post to be placed, then attach to it a few fronds of e.g. kiwakiwa, or some other item, and recite incantations over it, to imbue it with magical powers of protection.

Because of kiwakiwa’s particularly bitter flavour, Māori women sometimes used it as a rongoā, rubbing its crushed fronds on their breasts to wean children who were reluctant to give up the breast.

See also

Category

Botany 2016

In The Hills 2016-07 < Index chronological > In The Hills 2016-09