Ferns are abundant in all damp situations in New Zealand forests, forming the undergrowth beneath a dense canopy of evergreen trees. They are found growing also on trunks and branches of trees, on banks of streams, and in the open, even on dry hillsides. There are over 150 species found in this country, representatives of 12 families, and of these species 54 are not found elsewhere; they are endemic. It is not the number of species in New Zealand but their great variety which makes them so interesting, ranging from filmy ferns, only 1 in. high, to large tree-ferns, which often form part of the canopy of the forest.
Ferns may well be regarded as fascinating amphibians of the plant world, for there are two distinct stages in the life cycle of each plant, one of which is dependent on water. The fern plant with which we are familiar usually grows on land; it represents the asexual generation – the sporophyte – and bears spores on mature fronds. These spores are borne in cases, the sporangia, which are usually collected in groups or sori, on the under surface of the leaf. Each sorus usually has a protective covering, the indusium. The sori differ considerably in form and position and are useful as a means of identification. They may be in a cluster, in marginal lines, or the whole of a fertile frond may be entirely covered with spore cases. There is often an intricate mechanism for the release of the spores, each of which is capable of producing a new plant, but of a different form. This is extremely small, a thread-like or heart-shaped structure growing close to the ground, but is green and self supporting. This is the prothallus, and because it bears the gametes, or sex organs, is called the gametophyte. On it are produced male organs, antheridia, from which tiny free-swimming sperms are set free and depend on films of water for finding their way to the egg cells, still within the archegonium, embedded in the prothallus. When a sperm has fused with an egg cell the fertilised egg produces a new plant, unlike itself, the large, conspicuous sporophyte. Thus we see an alternation of generations, two types of plants; the sporophyte bearing asexual spores which give rise directly to the gametophyte on which sex organs are produced. The latter is seldom noticed; it is the sporophyte generation which we regard as the fern plant. Some ferns have also efficient means of vegetative reproduction as the underground stems of bracken, Pteridium esculentum, and the “sporelings” or “bulbils” on the surface of fronds of the hen-and-chicken ferns, Asplenium bulbiferium.
Among simple forms are two species of the adder's tongue, Ophioglossum, and the parsley fern, Botrychium australe, with finely divided leaves, and the allied mountain species, B. lunaria. In the north there is the magnificent king fern, Marratia salicinia, with fronds up to 12 ft long and queer, fused sporangia. Of the royal fern family, Osmundaceae, we have the fine Todea barbara of the far north, with its tall, stiff tufts of fronds, and its beautiful relative, the Prince of Wales feathers, Leptopteris superba, found in damp woods.
Vastly different are the small Schizaea spp., not at all fern-like in appearance, one of which, the fan fern, S. dichotoma, is found in kauri forests. Of the same family is that intriguing climber, the mange mange, Lygodium articulatum, which festoons forest trees, climbing by the midrib of the leaf. It is sometimes said to have the longest leaf in the world.
Five species of Gleicheniaceae are found here and they show more advanced forms. These are sun-loving ferns with an unusual method of growth. The frond divides into two branches; later each of these may divide again. The northern Gleichenia fiabellata and the widespread umbrella fern, G. cunninghamii, are both very handsome. G. dicarpa, common in swampy places, and G. microphylla are both heath-like plants. The tropical Dicranopteris linearis is found near hot springs of the thermal regions.
(The name Dicanopteris may now be used for Gleichenia, but the latter is the name by which the rather unusual genus is popularly known, and is used by Allan.)
A remarkable and very beautiful plant is Loxoma cunninghamii, with distinctive elegant triangular fronds up to 4 ft long. The little sori on the frond margin have their sporangia on tiny projecting columns. This is found only in the northern half of the North Island.
There are 28 species of filmy ferns of the family Hymenophyllaceae found in New Zealand. The fronds are thin and delicate and the sporangia are conspicuous; they are borne on receptacles which sometimes project from the margins of the leaves. Filmy ferns are found throughout the country; the largest forms and most luxuriant grow in the damp forests. They vary from the large Hymenophyllum dilatatum, which may reach 2 ft in height, to the tiny H. minimum, less than 1 in. high. Under suitable conditions Mecodium dilatatum may also grow to a large size, and other minute forms are Sphaerociarium lyalli and Craspedophyllum armstrongii. The kidney fern, Cardiomanes reniforme, with undivided leaves fringed with prominent sori, is common throughout the country. Some members of this family are matforming; others are tufted, as the lovely Mecodium pulcherrimum, the stiff little Selencodesmium elongatum with protruding receptacles, and Macroglena stricta.
Tree ferns are a conspicuous feature of the New Zealand vegetation; there are two genera: Dicksonia and Cyathea. Of Dicksonia there are three endemic species: (1) the widespread D. squarrosa, the silvery tree fern, which can produce stolons and thus colonise vegetatively; (2) D. fibrosa, with a mass of fibrous roots which sometimes form a trunk 2 ft in diameter; and (3) the woolly tree fern, D. lanata, which creeps on the ground. The genus Cyathea contains the largest and most beautiful tree ferns; there are eight species found here, four of them being common: (1) Cyathea medullaris, the black tree fern, or mamaku, with hexagonally marked black trunk, and black stemmed fronds up to 20 ft long; (2) Cyathea smithii is recognised by the light-brown stalks of dead fronds which persist and stand out round the stem like a ballet skirt; (3) the silver king, C. dealbata, easily recognised by the white-backed fronds; (4) the mountain tree fern, C. colensoi, which is semi-prostrate and lacks an indusium. There are two fine species found in Kermadec Islands. The genus Cyathea is distinguished from the genus Dicksonia by the presence of scales on the fronds; the latter has bristly hairs, moreover, the sori of Cyathea are round and away from the margin of the leaf, but in Dicksonia the sori are marginal with a two-valved indusium. The young fronds of Cyathea medullaris are beautiful as they first appear, tightly coiled, covered with large, shiny brown scales, and then as they gradually uncoil, still with these brown scales.
In open country, by roadsides and streams, and covering hillsides, a great variety of ferns is found. The ubiquitous bracken, Pteridium esculentum, the farmer's misery, grows to 6 ft in height and spreads rapidly by means of rhizomes. These are starchy and were used by the Maoris both as food and as medicine. The lace fern, Paesia scaberula, is less troublesome but may over-run considerable areas; it is light green, sticky, with finely cut fronds. Histiopteris incisa is a large wayside fern. Particularly in the south it grows with the tall Hypolepsis tenuifolia and the smaller H. rugosula. On roadsides, as well as in forests, is found the large tufted Cyclosurus penniger. In swamps in the North Island are Thelypteris palustris and three species of Cyclosurus. C. gongylodes is common near thermal springs. These latter are commonly known as species of Dryopteris. Cystopteris is a genus of small ferns with pale membranous fronds found throughout the country in dry open places, in clefts of rock, and in mountain districts. Three species of Lindsaea of the family Pteridaceae are L. viridis, a beautiful little fern with narrow, pale green fronds, found on the banks of streams; more widespread, especially in the North Island, is L. trichomanoides, with golden brown stems, found in dry places; and L. linearis, with small, narrow fronds, found amongst the manuka and light scrub in many localities. There are two species of Pellaea, of which P. rotundifolia is usually regarded as a drought-resisting fern and is very common, but P. falcata, of similar dry habitats, is comparatively rare.
Two large genera worthy of note are Blechnum and Asplenium. There are about 15 species of the genus Blechnum in New Zealand, mostly ferns with simple leaflets (pinnae). The Cape Blechnum, B. capense, is a feature of the landscape almost everywhere, on roadside cuttings and banks of streams. The young fronds are of reddish colour, and mature fronds may grow to nearly 10 ft. B. discolor has stiff, green fronds, whitish below, and it spreads freely by stolons. The same habit of vegetative reproduction is seen in the “miniature tree fern”, B. fraseri, with a small crown of leaves several feet above the ground. B. filiforme has a juvenile form with small, rounded leaves, but the mature form is a climber with long, pointed, sterile fronds, up to 30 in. long, and very narrow fertile fronds. B. membranaceum, B. lanceolatum, and the large B. norfolkianum are closely related forms. Two seaside species, B. durum and B. banksii, are common, especially in the south. Throughout the genus the fertile fronds are very narrow, purely spore bearing, and differ greatly from the sterile fronds which provide the food for the plant.
Closely related to Blechnum is Doodia, two species of which are common. In the north D. media covers whole hillsides with its autumn coloured fronds. D. candata is smaller, not so common, and found only in the North Island.
There are about 15 species of spleenworts, genus Asplenium. Some of these have simple leaflets, as A. lucidum, the beautiful widespread shining spleenwort, and the shore spleenwort, A. obtusatum. Among species with more divided fronds is the hen and chickens, A. bulbiferum, which bears tiny young plants on the surface of the frond. The somewhat similar A. lamprophyllum contains oil of wintergreen. A. flaccidum is found in several forms; it may grow erect from the ground, but is best known as it hangs from the branches of trees with long, narrow, drooping fronds of a leathery texture.
There are in New Zealand five species of the shield fern, genus Polystichum, one of which has been reported only from Kapiti Island. The scaly shield fern, P. vestitum, forms a prominent feature of forest, especially in the south, where its dark-green leaves form a spreading crown up to 6 ft across. P. sylvaticum is smaller, while P. cystostegia, with rather pale-green fronds, is found in alpine regions. P. richardii is very dark green, harsh to the touch, and the large, rounded sori are covered by an indusium with a central black spot. This species is fairly common, and often found near the sea.
The genus Lastreopsis is represented by the widespread hairy fern of the forests and the velvet form, L. velutina, of dry places. L. glabella and L. microsona have similar finely cut fronds.
Six species of maidenhair ferns are found in New Zealand, the most common of which are Adiantum cunninghamii and the closely related A. fulvum. Growing in the sun is A. aethiopicum and A. hispidulum, with bristly hairs and autumn coloured young fronds. The large A. formosum is found in only a few places in the North Island, while A. diaphanum is a modest little form common in shady places.
There are but two species in New Zealand which grow only in water. One is the common Azolla, and the other the rarely found Pilularia. Neither of these is very fern-like. Azolla filiculoides, var. rubra, is found as a thick covering over large areas of ponds and slowly moving streams. Each plant is very small with overlapping leaves which enclose air and this enables the plant to keep above water. Pilularia novaezealandiae has tiny grass-like leaves; the spores are in small rounded structures resembling “pills”.
Climbing ferns are a feature of our forest, and there are also many perching ferns. Some of these have been mentioned already as mange mange, Lygodium articulatum, which climbs by its midribs, the perching Asplenium flaccidum, and others. The Polypodiaceae is a large family of ferns, mainly of climbing or creeping habit. The fronds are usually simple, firm or leathery in texture, with prominent sori and covered on the under surface by light-coloured hairs. Five genera are represented in New Zealand, the names of which have undergone various changes, as shown in brackets. The genus Pyrossia is represented by P. serpens (Cyclophorus serpens), with a large rhizome thickly covered with brown scales it climbs up trunks of trees or over rocks. This small fern is found everywhere, the very thick leathery entire leaves vary in shape, and have a thick felting of star-shaped hairs. There are three species of the genus Microsorum (Phymatodes or Polypodium), M. scandens, with long, much branched rhizomes, covered with dark-brown scales, and M. diversifolia, with irregularly lobed, bright-green fronds. Both are very abundant on trees and rocks. M. novae zealandiae is a larger fern with stout rhizomes and large leaves, deeply cut; it is confined to forests in the North Island. There are four species of the genus Grammatis (Polypodium) which are small perching ferns. Anarthropteris lanceolata (Polypodium) represents another genus; it has simple, bright green, rather fleshy leaves, and is common on tree trunks, especially in the north. Ctenopteris heterophylla (syn. Polypodium grammatidis and Grammatis heterophylla) is abundant throughout the country as an epiphyte.
Our ferns provide much of interest. A number hybridise vigorously; some have variant forms not fully understood, and probably with further research the number of our species will be increased. In the meantime many problems await the keen investigator. A rich field is open also to the horticulturist, since many of our species are easy to grow. From various points of view, then, New Zealand can count itself fortunate in its rich bounty of ferns.
Note: The names used in this article differ in some cases from those in Allan's Flora. As regards the Hymenophyllaceae, Mecodium, Sphaerocionium, Craspedophyllum, and Apteropteris are listed in Allan as subgenera of Hymenophyllum and Macroglena; and Selenodesmium and Cardiomanes as sub-genera of Trichomanes. Allan's names are listed in brackets in the following list of generic names: Leptopteris (Todea), Dicranopteris (Gleichenia), Cyclosorus (Thelypteris), Microsorium (Phymatodes), Lastreopsis hispida (Rumohra hispida).
by Marguerite Winifred Crookes, M.A., Botanist, Auckland.