In The Hills In The Hills 2016-05

Blechnum chambersii < Species index > Blechnum discolor

This article was first published in the Tararua Tramper Volume 88, no 4, May 2016

May in the hills with Barbara Mitcalfe and Chris Horne

Blechnum colensoi, peretao, Colenso's hard fern

Sterile peretao fronds with one fertile frond Photo: Jeremy Rolfe

Many trampers are likely to be familiar with this handsome, endemic ground fern of wet gullies, often beside deeply shaded waterfalls where it is recognised by its large, glossy, deep-green, pendulous fronds hanging down steep banks.

Fronds

Like most Blechnum species, Blechnum colensoi's fertile fronds are very different from its sterile fronds. If you look at the image on this page, you will notice a very skinny, sinuous frond sprawling to the left, rather like a big green fish skeleton! This is the fertile frond, covered all over with green sori containing unripe spores, too tiny to be visible in this image.

When the spores ripen and fall to the ground, they will germinate and undergo the several stages of development into adult ferns, (e.g., prothallus; sexual differentiation; reproduction), which we described in the December 2015 Tramper.

Peretao's glossy, sterile fronds vary from 20 cm to one metre long and from 12-20 cm wide. Each frond usually has c. 10 pairs of broad, elliptic segments, each up to 20 x 4 cm, with a very firm, leathery texture and smooth margins which taper to a fine point at the tip. As you will notice in the image, an unusual feature of these segments is that they do not taper to join on to the frond's midrib, but are attached 'squarely' on to it by the whole width of their broad bases. This type of attachment is referred to as 'decurrent'.

Distribution

Peretao is common in wet, lowland to montane forests from Hokianga Harbour southwards, and also in the South, Stewart, Chatham and Auckland islands.

Uses

Peretao is a significant member of a specialised community of plants and animals which require high amounts of shade and ambient moisture to survive and thrive, e.g. mosses, liverworts, ferns and many other species. Its long, broad fronds provide shade and a splash-back surface which re-distributes falling water.

Its handsome, luxuriant appearance adds greatly to the beauty of waterfall sites with which it is so often associated, enhancing their appeal to trampers and tourists alike, especially when they can include this distinctive fern in their photographs. Some people even call it ‘waterfall fern’.

See also

Category

Botany 2016

In The Hills 2016-04 < Index chronological > In The Hills 2016-06