In The Hills In The Hills 2015-10

Asplenium flaccidum < Species index > Asplenium polyodon

This article was first published in the Tararua Tramper Volume 87, no 9, October 2015

October in the hills with Barbara Mitcalfe and Chris Horne

Having recently introduced you to some NZ conifers, we are now leaving that topic. Early last year we described five NZ tree ferns and this month we start on some NZ ground-fern species.

How do ferns differ from flowering plants?

There is a fundamental difference between ferns and flowering plants. A fern has neither flowers nor true leaves. Instead, it has fronds, which have a dual function – the upper surface of a frond converts visible light into energy, but if you turn it over, you will see that the underside has sori, containing spores, which are reproductive organs.

By contrast, flowering plants have true leaves, the sole function of which is to convert visible light into energy, and they have separate, specialised structures for reproduction, namely flowers.

Fern rhizomes

All ferns have a rhizome, which is defined botanically as a type of stem. Some fern rhizomes creep along the soil surface, e.g., kidney fern. Some ferns have a climbing rhizome, e.g., mokimoki, climbing hound's tongue. Some ferns have a tall, solid rhizome like a trunk, e.g., all tree ferns. Some fern species, e.g., our fern-of-the-month, shining spleenwort, has an erect, above-ground rhizome from which the fronds emerge above and roots develop below. Young fern fronds emerge tightly coiled in a koru shape, (of recent flag fame), an elegant growth form almost never seen in other plant groups.

Asplenium oblongifolium Photo: Jeremy Rolfe

The Asplenium genus

The Asplenium genus is one of NZ's largest fern genera, with more than 20 species or sub-species. Derived from Greek, the name means 'no spleen', referring to an early belief that spleenworts provided a remedy for ailments of the spleen.

Asplenium oblongifolium, Huruhuru whenua, Shining spleenwort

This handsome endemic fern is common in a wide variety of sites and conditions, in coastal to lower montane areas in the North Island, and in coastal areas in the South Island as far south as Banks Peninsula and Greymouth. Look for it on rugged, coastal cliffs, open scrub, or deep in shady forest. Usually terrestrial, it is sometimes epiphytic. Its rhizome is densely covered in dark brown scales. In exposed, well-lit sites, the fronds are usually pale green. In shady forest the mature fronds are a glossy, dark green (see image) up to 1000 mm x 350 mm. Its 16-40 alternate segments are pinnately arranged and look just like leaflets. They are 40 – 250 mm x 10 - 40 mm, with slightly serrated margins and a fairly firm texture. Look at their undersides to see neatly parallel rows of sori, each up to 20 mm long, in a herringbone pattern, from which ripe spores are distributed by the wind. You may find it useful to remember that most species of Asplenium have a herring-bone pattern of sorts.

The species name oblongifolium refers to the generally parallel-sided frond segments that taper to points at their tips. Lastly, shining spleenwort's glossy fronds make it easy to identify. The Māori name huruhuru whenua is a metaphor for the body-hair of the land.

Uses

To some Māori, huruhuru whenua was sacred. Tōhunga / priests used it in some spiritual rituals. Māori would placate Tāne, god of the forest, by placing fronds of huruhuru whenua over the stumps of trees they had felled to make waka / canoes. They ate the koru/young shoots as a green vegetable, which William Colenso, an early missionary, described as succulent.

Cultivation

Huruhuru whenua is very easy to grow. Another pleasing feature of it is that it often self-sows in gardens and on road-side banks, its spores having been carried there by the wind. Look for it in lightly-shaded, damp sites in your garden – you may find that it has already arrived.

See also

Category

Botany 2015

In The Hills 2015-09 < Index chronological > In The Hills 2015-11