July in the hills with Barbara Mitcalfe and Chris Horne
Blechnum filiforme, pānako, thread fern, climbing hard fern
If you're tramping in forest and notice a fern climbing high on tree trunks, it's almost certainly pānako, Blechnum filiforme, the only blechnum species which is high-climbing. It is found in coastal and lowland forests in the North Island and the northern coast of the South Island. This NZ endemic fern is unique in having three types of fronds: juvenile; sterile adult and fertile adult.
On the ground, you will see some small, deep-green, juvenile fronds creeping over banks and rocks before beginning to climb. These little fronds are narrowly elliptic, usually no wider than 5 cm and only up to 25 cm long, with 15–20 pairs of coarsely-toothed segments either side, each only 5-25 x 2–8 mm. (See image no. 1).
2. Sterile adult
As pānako's thin, dark, scaly rhizome elongates itself and begins to climb vertically, clinging closely to the tree trunk, it sprouts dense trusses of adult, sterile fronds as it goes. These bright-green fronds get much bigger as they mature, often reaching c. 60 x 15 cm, and almost completely covering the tree trunk. They have up to 30 pairs of segments arranged pinnately on the rachis, (i.e., in pairs along the stem), each segment narrowly elliptic, toothed, stalked, up to 9 x 5 cm, and tapering to a fine point, rather like Asplenium polyodon. (See image, In The Hills February 2016).
3. Fertile adult
You may recall that the sterile fronds of all blechnum species are different from the fertile fronds. When pānako's growing tip has reached a height of c. 2 m up the tree trunk, it starts to produce its third type of frond. These are about the same size as the sterile ones, i.e., c. 60 x 15 cm, but otherwise they are completely different - delicate and fertile. Many fine, flexuous, thread-like strands sprout from each side of the rachis. (See image no. 2). They are so flimsy that even a light breeze causes them to quiver. Hence the names, “filiforme” and “thread fern”.
Despite their apparent fragility, these fertile fronds contain the spores, which ripen and reproduce as usual, via prothalli, etc., just as we have described for other ferns.
Pānako is highly decorative, adding its own distinctiveness and amenity to the forest ambience. Along with all other green plants, it contributes to the supply of oxygen. We do not know of any rongoā uses.
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|Blechnum filiforme||Pānako||Thread fern; Climbing hard fern||2016-07|
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