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.

Figure 33 (opposite) An entanglement of supplejack (Ripogonum scandens).
Photo: M. D. King.

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.

There is a very marked difference in size and shape between juvenile and adult leaves in this species (Fig. 34). The seedlings establish them-

Figure 34 The vine Parsonsia heterophylla. Juvenile foliage: right. Adult foliage and leaves: left. Photo: J. E. Casey.

page 58selves in sometimes quite shady places on the forest floor and the first few leaves produced are small and almost circular. These are followed by leaves tending towards the second type of juvenile leaf, which is long and narrow with smooth or wavy margins. Intermediates may be narrow at the base and round at the tip, or narrow at the base and tip and round in the middle, and, to make matters even more complicated, lateral branches on the seedlings usually repeat the same sequence. The result is a bewildering and apparently random arrangement of leaf forms. Some of the seedlings are completely green, others are largely brown and some leaves of the latter are unusually attractive with a mosaic of green, dark brown and pale brown patches.³⁹ The adult leaves, which are formed when the stems reach full light, are much larger and broader and generally uniform in shape, although there are often modest differences in shape between different vines.

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).

Figure 35 Stem of a young matai (Prumnopitys taxifalia) distorted by a twining vine (possibly Parsonsia heterophylla) which subsequently died.
Photo: J. W. Dawson.

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.