Forest Vines to Snow Tussocks: The Story of New Zealand Plants
Vines whose foliage eventually spreads into the canopy of the forest are usually woody and are often referred to as lianes.36 At the adult stage they are light-demanding and generally produce flowers, or spores, only in well-lit situations. Young plants on the forest floor are more shade-tolerant, but nevertheless establish most abundantly in the better lit earlier stages in forest development or in canopy gaps in mature forest. Unlike the sub-canopy climbers, the lianes climb by a variety of means — attaching roots, twining stems, hooks and tendrils.
The most prominent root climbers are the climbing ratas,37 currently included in the genus Metrosideros. They are able to grow up quite large trunks and are perhaps most abundant on the emergent conifers and the northern rata. Their climbing stems are usually quite slender and the leaves, which form a close mosaic on the tree trunk (Fig. 30), are generally smaller, thinner and more rounded than those of the adult stage. When the stems reach full light high in the tree crown, or adequate light in the lower levels, they form a bushy growth of branches which extend away from the support and eventually bear flowers. At this stage the stems extending up from the ground enlarge considerably and swing away from the host trunk as woody cables (Fig. 31). Metrosideros fulgens and M. perforata form the largest stems, sometimes up to 15 cm or more in diameter, but the others may attain 7-8 cm. Often no leaves are visible near the ground, but the stems can be identified to some extent from the bark — M. perforata has red-brown stringy bark, M. fulgens also red-brown bark separating in thickish strips and the other species have pale whitish bark separating in thin flakes.
Metrosideros albiflora and M. carminea are restricted to the northern North Island. M. albiflora is most common in kauri forests. It has the largest leaves of the group and small, white flowers. M. carminea is much rnore colourful, with masses of large, crimson flowers, and it is now popular as a garden plant. M. perforata, M. fulgens and M. diffusa frequently occur together as far as the northern South Island and M. diffusa continues alone to Stewart Island. M. diffusa often forms slender stems near the ground which spread widely in the humus of the forest floor and climb any trunks they encounter. M. colensoi also reaches the northern South Island, but is more localised in its occurrence, favouring forests on fertile soils such as those of river terraces. The strongly weeping habit of its foliage is a distinctive feature. M. fulgens has large flowers ranging in colour from orange to dark red, while the other species have small white to pinkish flowers. Most of the climbing ratas flower from early to mid-summer, but M. carminea flowers in early spring and M. fulgens is remarkable both for the timing and length of its flowering season — the first flowers may appear in late summer and flowering continues through the winter into early spring.
Figure 31 (left) The cable-like stems of a mature Metrosideros perforata on a rimu (Dacrydium cupressinum). Kaitoke, near Wellington, southern North Island. Photo: M. D. King.
Figure 30 (above) Young stage of white climbing rata (Metrosideros perforata) forming a leaf mosaic on a tree trunk.
Photo: B. V. Sneddon.
The only other root climbing liane in New Zealand is the kiekie (Freycinetia baueriana var. banksii). It belongs to a distinctly tropical family, the Pandanaceae, which is represented by many species of Freycinetia and Pandanus in tropical rain forests. One might expect that the outlying New Zealand species would be of reduced form and perhaps rare. In fact it compares with the largest and most robust tropical species and page 55is abundant in lowland, especially swampy forests as far as the south west of the South Island. Tree trunks are often completely obscured by the foliage of kiekie (Fig. 32), which can extend into the highest crowns 30 m or more above the ground. The leaves are dark green, narrow and a metre or more long with finely toothed cutting edges. The male and female inflorescences found on separate plants are cone-like and surrounded by leaf-like white or purplish bracts, which are sweet and edible. The stems are a few centimetres in diameter and distinctively ringed with leaf scars. They give rise to slender, attaching roots, which branch freely towards their ends and attach themselves firmly to the trunk. Other roots are stouter and grow down the trunk to the ground, often building up into quite thick and rather untidy masses.
Twining Stem Climbers
Twining lianes have climbing stems which wind around their supports in a clockwise or anticlockwise direction, depending on the species, until they reach the full light of the forest canopy. Unlike root climbers, many twiners are not able to climb large tree trunks — their turning circle is too small for that — so they either have to climb young slender trees and grow with them into the canopy or climb small or young subcanopy trees and transfer from their crowns to those of taller trees. Many twiners also climb stems of their own species which have already gained the forest roof.
Undoubtedly supplejack (Ripogonum scandens), which ranges throughout the country, is the most familiar twiner in New Zealand forests,38 particularly on alluvial and swampy sites. It belongs to the lily family, taken in a wide sense, and its almost black, jointed, bamboo-like climbing stems often form entanglements that greatly impede progress (Fig. 33). Fortunately, unlike several of its relatives in Australia, supplejack does not have prickles. Aggregations of woody, tuber-like rhizomes below ground give rise to the climbing stems which are dark-brown to black, 1-2 cm in diameter and which bear pairs of long narrow, often twisted scales in place of leaves. The stem tips are reminiscent of Asparagus and are soft and easily broken. They can elongate at an average rate of 5 cm per day in summer and while growing upwards the upper part of the shoot revolves slowly in an anticlockwise direction. If it does not encounter a support it bends down to the ground and grows up again from the tip.page 56 page 57
Supplejack mostly climbs fairly slender supports, but can also twine around quite large trunks, the record being a kohekohe of 1.5 m diameter.38 When a climbing stem reaches the forest canopy, lateral climbing stems arise from its upper parts and eventually bear relatively slender, leafy stems of limited growth, which are unable to twine. The leaves are broad and distinctively veined with two strong lateral veins more or less parallel to the midrib. The leafy stems bear small flowers followed by bright red berries. When lateral climbing stems are formed near the ground they are often swollen-and tuber-like at the base and produce roots which may descend more than a metre to the ground. Supplejack is restricted to New Zealand, but other species of Ripogonum are found in eastern Australia and New Guinea.
The two species of Parsonsia, sometimes known as native jasmine, are found in lowland forest and shrubland throughout the country, Parsonsia heterophylla is the larger of the two, with stems up to 10 cm in diameter which attain heights up to 20 m above the ground. It is commonest near forest margins, but can reach the crowns of taller trees deeper in the forest by spreading from lower to higher levels in the forest canopy.
Figure 34 The vine Parsonsia heterophylla. Juvenile foliage: right. Adult foliage and leaves: left. Photo: J. E. Casey.
The seedlings, which rotate in an anticlockwise direction at their tips as they grow upwards, reach about 45 cm in height without support and somewhat higher if two or more seedlings twine about each other. If no support is encountered then the stems bend down to the ground and grow along it until they find something to climb. The supporting stems are usually slender, although Parsonsia heterophylla has been observed climbing tree trunks of up to 25 cm in diameter.
Parsonsia capsularis has small flowers, different in form from those of P. heterophylla, but the adult leaves of some varieties of the two species are very similar. P. capsularis also has long, narrow, reddish-brown juvenile leaves, and in some cases these are retained at the adult flowering stage. This is a smaller plant than its more common relative and grows in shrub communities and, less often, at forest margins. The small, fragrant flowers of these two species are borne in clusters and are white, yellow or, in the case of P. capsularis only, red. The fruits are pod-like, hang downwards and split open to release numerous seeds, each with a dense tuft of hairs for wind dispersal.
The distinctive juvenile forms of our parsonsias are not peculiar to New Zealand. The phenomenon is also found in species in eastern Australia and New Caledonia. The genus ranges from tropical Asia to the Pacific.
Two species of Muehlenbeckia are twining lianes common throughout New Zealand in lowland to montane forests. M. australis is the larger species and its seedlings are often abundant on the forest floor in both page 59shady and well-lit places, but mature plants are most commonly found at forest margins or in regenerating forest. The young stems bend to the ground if they don't find support, branch, and then spread on the forest floor. Unlike most other twiners the erect stems rotate in either direction and in some cases change direction when they begin to climb. The supports are always slender and often become very deformed as they expand within the coils of the vine. Sometimes they die, and this may be caused by the vine, but at other times it is the latter that dies, leaving as evidence on the supporting stem a pronounced helical groove (Fig. 35).
By climbing up smaller trees Muehlenbeckia australis may extend into the crowns of tall trees 30 m or more above the ground. A distinctive feature of M. australis is its formation of firm cane-like 'searcher shoots' during the autumn from any part of the stem system. Where these arise on stems coiled on the forest floor they grow erect for several metres, beginning to rotate only after the first metre. Where they develop on stems in the tree crowns they extend more or less horizontally, often from one tree crown to another, and in this way the vines become extremely widespread through the forest canopy. In fact, there sometimes seems to be more of the draping foliage of the Muehlenbeckia, particularly in second growth forest, than of the trees themselves. The adult leaves are several centimetres long; broad, thin and pale green, sometimes with a drawn-out tip. Juvenile leaves are much smaller; round, oval or sometimes, fiddle-shaped.
Muehlenbeckia complexa is similar in its growth habit to M. australis, but it is smaller in all respects and grows on shrubs or small trees at forest margins or in shrub associations. The leaves are only about 1 cm long, more or less circular and a little thicker than those of M. australis. The New Zealand species of the genus are largely endemic although M. australis occurs on Norfolk Island. The genus also occurs in southern South America and Australia.
Tecomanthe speciosa is undoubtedly New Zealand's rarest vine in nature, only one plant having been discovered, on the Three Kings Islands. It has robust twining stems which, in cultivation, extend high into supporting trees. The leaves are pinnately compound with quite large leathery leaflets and the tubular flowers, although large, are of an inconspicuous cream colour. Most of the other species of Tecomanthe are found in New Guinea.
Mangemange (Lygodium articulatum) belongs to a largely tropical genus of ferns unique because of their ability to climb by twining; although in this case it is not the stems which twine but the axes of compound leaves, which have indefinite growth and sometimes extend from the ground to the tops of high trees. The New Zealand species is restricted to the north of the North Island, but there it is common, particularly in kauri forests. The true stems spread over the forest floor. The axes of the leaves arising from these are slender and wiry and often twine about each other as well as their supports to form springy masses on the ground, in well-lit places or on the forest roof. Compound leaflets page 61arise from the twining axes and, in well-lit situations, these may be fertile with narrow segments, each with two close-set rows of sporangia.
Twining Leaf Petiole Climbers
It might be wondered why the fern Lygodium, with its twining leaves, is not included here. Leaf climbers are defined as plants whose stems are supported as they grow upwards by the sensitive petioles (stalks) of their otherwise unmodified leaves, which wind round any slender supports with which they make contact. In Lygodium the true stems remain on the ground, but the primary axis of the leaf is like a twining stem in its indefinite growth and indefinite ability to twine. Indeed it takes a botanist to appreciate that with Lygodium we are dealing with twining leaves rather than twining stems, so it seems more realistic to treat it as a twiner rather than a leaf climber.
New Zealand representatives in this category are all species of Clematis, a genus which is widespread in temperate regions and also found in the montane tropics. The best known and largest New Zealand species is Clematis paniculata, which is found in lowland forests throughout, particularly marginally, and is greatly appreciated in the spring when its sprays of large, pure-white flowers stand out against the dark foliage of the forest. The adult leaves are divided into three leaflets, which are broad, dark-green, and smooth-margined. Leaves on young plants on the forest floor are very different. The first leaves are long, narrow, membranous in texture and undivided. These are succeeded by compound leaves with three narrow leaflets. In subsequent leaves, the leaflets become deeply lobed, broader, and, where light is adequate, gradually trend to the adult form. Similar juvenile leaves have been reported for Clematis species in eastern Australia. Seedlings rotate in an anticlockwise direction and are able to twine around slender supports. Similar twining ability, at least when young, has been recorded for some other leaf climbers outside New Zealand; nevertheless the primary mechanism for climbing is the clasping leaf petiole.
When a leaf is formed at a stem apex it is first erect, then gradually bends downward until it projects at right angles to the stem. The petioles of the leaf as a whole, and of the leaflets, are well developed at this stage and if any of them touch a suitable support they are stimulated, by a process not yet understood, to wind round it. The portion of the petiole in contact with the support enlarges and becomes page 62strengthened. Clearly the leaves cannot attach to large supports, so where a large stem of Clematis paniculata up to 10 cm in diameter ascends to a tree crown 10 m or more above the ground, it must have attained that position via smaller trees and shrubs.
The four or five other climbing New Zealand species of Clematis are smaller than C. paniculata. They are incompletely known and in some cases not yet clearly defined. Several grow at forest margins, including C. forsteri and C. foetida, and some also grow in shrubland.
Tendrils are similar to the petioles of leaf climbers in that they are sensitive to touch and respond by twining round a support. They differ in that they are derived from plant organs — branches, inflorescences, leaves or leaflets — which have completely lost their original function and are used solely for climbing. Further, once a tendril has attached to a support, it coils into two opposed helices in its free part, which increases its elasticity and also draws the stem closer to the support.
In New Zealand we have only one forest liane which climbs by tendrils. This is the native passion vine, Passiflora tetrandra, which ranges through the North Island and down to Banks Peninsula on the east of the South Island. The leaves are dark green and shiny and drawn out to a point at the tip. The flowers are much smaller and less colourful than those of the cultivated species and less elaborate in their form, but the fruit compensates for this by being bright orange and 2-3 cm in diameter; it is greatly sought after by birds.
The tendrils arise in leaf axils and are considered to be modified inflorescences. They are at first erect then bend downwards; if they encounter a slender support they wind round it. The part in contact gradually becomes thickened, until it is about twice the diameter of the free part of the tendril. The native passion vine is most common in the lower marginal parts of forests, but it spreads so effectively over the forest roof that it frequently reaches the tops of taller trees. The woody stems can be up to 12 cm in diameter and in their lower parts often form tortuous coils on the forest floor.
The New Zealand hook climbers are all species of Rubus, a genus which includes the familiar blackberry and raspberry and is widespread in page 63temperate regions and the montane tropics. In north temperate regions, the species of Rubus do not climb and are shrubs or scramblers in open habitats, but most of the New Zealand species and a number of Australian and tropical species are low to high climbing forest lianes. The adult leaves of most species are palmately compound with three or more leaflets. Backwardly curving hooks or prickles stud the underside of the petioles and leaflet midribs and sometimes the stem as well — a feature which effectively prevents the stems slipping back from any position attained. In colonial times, this tenacity earned for the New Zealand plant the name of 'bush lawyer', a perhaps unwarranted slur on the legal profession of the day. In fact the 'lawyers' are the only plants in New Zealand forests which are prickly. This is in contrast to the rain forests of Queensland and south-east Asia where many spiny climbers are unpleasantly in evidence. The original lack of browsing mammals in New Zealand is the probable explanation for this, and the same would apply for the lack of spiny plants in New Caledonian forests.
The bush lawyers are sometimes included in the 'scrambler' category of vines. Scramblers are small, unspecialised climbers whose weak, drawn out stems grow up between the branches of shrubs and trail over them. The lawyers begin their ascent in a similar way, but their hooks enable them to reach great heights, equal to those attained by more specialised vines.- For this reason I think they warrant a special category. The liane species of New Zealand Rubus occur throughout the country, including Stewart Island, in lowland to montane forest.
The first leaves of the young plants are simple; their stems are quite stout and so are able to stand erect without support for 60 cm or more. If nothing is available to climb, the young plant bends to the ground, branches and spreads widely over the forest floor until some of the branches find supports and make their way into the forest canopy via shrubs and smaller trees. The woody stems, which can be looped on the forest floor as well as extending to the forest roof, frequently produce 'searcher shoots' (Fig. 36). The searcher shoots which are near to the ground can stand without support for one metre or more, and are thus very effective in expanding sites of Rubus foliage in the canopy and in establishing new sites.
The commonest species is Rubus cissoides which has long, narrow and sharply toothed leaflets. The adult stems may be up to 17 cm in diameter and the foliage can reach to 15 m or more above the ground.page 64
Rubus schmidelioides has stems up to 10 cm in diameter, and generally smaller, similarly shaped leaflets, but these leaflets are bluntly toothed and have a dense covering of whitish hairs beneath.
Rubus australis is most common in swamp forest and is sometimes referred to as 'swamp lawyer'. Its leaflets are short, fairly broad and sometimes almost circular. In this species there is a distinct juvenile form, which spreads and roots widely over the forest floor, bearing leaves with small, membranous, more or less round leaflets with reddish coloured veins. At the adult stage this species can reach for 10 m or more into tree crowns, with stems several centimetres in diameter.
Rubus squarrosus is perhaps the most remarkable of the genus, as, in open situations and on shrubs, the leaflet blades remain undeveloped and the leaves consist of rather elongated petioles and the almost threadlike midribs of the leaflets, all beset with yellow prickles (Fig. 37). Such leaves are very effective in clinging to any support. When the stems reach into tree crowns there is a trend towards normal leaves with well formed narrow leaflets. This species is similar in eventual height and stem size to R. australis.