Kingdom: Plantae
Division: Pteridophyta
Class: Pteridopsida
Order: Athyriales
Family: Blechnaceae
Genus: Blechnum (hard ferns)
Species: B. chambersii
Binomial name: Blechnum chambersii
Synonyms: Austroblechnum lanceolatum, Blechnum lanceolatum, Spicanta lanceolate,  Stegania lanceolate, Struthiopteris lanceolate, Lomaria doodioides, Lomaria lanceolate, Blechnum aggregatum, Blechnum doodioides, 
Common names: Lance Water-fern, nini, rereti

Blechnum chambersii (Austroblechnum lanceolatum) is a compact small slow growing ground fern usually found in deeply shaded banks especially along streams. It is a common fern found in damp areas of all New Zealand forests. It is also found in Australia and Fiji. It has a stout and erect rhizome that sometimes develops into a trunk. It has deep green lance-shaped fronds (15 to 50 cm long and 4-6 cm wide) that are coarsely dissected and can have up to 15 to 40 alternate pinnae. It has sterile and fertile fronds which are usually shorter.
Blechnum chambersii is very similar to Blechnum membranaceum and the two species will hybridise.

Early Maori use the young fronds in hangi cooking as a form of greens. 

Blechnum chambersii Nini-001.JPG

Blechnum chambersii Rereti.JPG Blechnum chambersii Lance Water-fern-5.JPG

Underside of frond
Blechnum chambersii Lance Water-fern-9.JPG

This is the end of the spore-bearing frond. The narrow leaflets on this frond will develop spores in clusters of sporangia which are called sori along the underneath side of the leaves. The edge of the leaves rolls inwards to protect the developing sori.Blechnum chambersii Lance Water-fern-11.JPG

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0