Vines
Subcanopy Climbers

Vines in this category are herbaceous and attach themselves to tree trunks by special roots arising from the stems. They ascend for varying distances up the trunks, but mostly do not enter the tree crowns. They are all able to reproduce in the reduced light of the forest interior.

In New Zealand all vines in this category are ferns and in some, as in the climbing members of the arum lily family in the tropics, there is a remarkable increase in size and complexity of the leaves as their height above the ground increases. The best known example of this is Blechnum filiforme (Fig. 27), a common plant in lowland forest as far south as the northern South Island. Blechnum filiforme is often abundant on the forest floor where it spreads by slender rhizomes.³³ In this situation the leaves are only about 10 cm long and once-pinnate, with leaflets which range in shape from small and oblong to almost round. Where the stems grow up tree trunks, as they frequently do, the leaves produced become progressively larger, until several metres above the ground they attain a maximum length of almost 35 cm and have long, page 47

Figure 26 Kahikatea (Dacrycarpus dacrydioides) with asteliad nest epiphytes. The tree originally had two trunks. The nearest one has fallen and its crown and epiphytes can be seen in the foreground. Te Marua near Wellington, southern North Island. Photo: M. D. King

page 48

Figure 27 (left) Leaves of the climbing fern Blechnum filiforme. Top right, a small leaf from the base of a tree trunk. Left, large leaf from 2 m above ground level. Lower right, fertile leaf.
Photo: M. D. King.

Figure 28 (right) Leaves of the climbing fern Arthropteris tenella. Top left, climbing stem with small juvenile leaves. Top right, large adult leaf. The other leaves are at intermediate stages.
Photo J. E. Casey.

narrow, pointed leaflets up to 10 cm long. It is among these largest leaves that the fertile, spore-bearing fronds, with their almost threadlike leaflets, are produced. The leaves of this species are dark-green and fairly thin. The climbing stems branch and the branches tend to stay close together and grow more or less vertically, sometimes reaching as high as 10 m above the ground.

Arthropteris tenella (Fig. 28) also has relatively thin, dark leaves and slender, vertically ascending stems, but these generally reach to only a few metres above the ground. This species also reaches the northern South Island, but is less common than Blechnum filiforme and is mostly encountered in coastal forests and some low altitude inland locations. The juvenile leaves are 5-10 cm long, once-pinnate and often rather peculiar in appearance — the few pairs of lateral leaflets are small and page 49

Figure 29 Phymatosorus scandens growing up a tree trunk. The simple leaves are juvenile and compound leaves adult.
Photo: J. E. Casey.

almost circular; the terminal leaflet is much larger and longer, narrowing to a point. Fully adult leaves are 30 cm or more long with many pairs of narrow, wavy-margined leaflets up to 8 cm long.

The light green, thin-leaved Phymatosorus scandens also shows a trend from juvenile to adult leaves with increasing height (Fig. 29), but in page 50this case the juveniles are about as long as the adults, up to 35 cm, but are narrow, undivided and usually sterile. There is often a fairly abrupt change to the adult leaves, which are much wider and are deeply incised into a number of narrow, lateral segments bearing sporangia.³⁴ This species often occurs with Blechnum filiforme in lowland forests, sometimes on the same tree, but it ranges further to the south of the South Island. It is able to climb vertical tree trunks with its slender stems spreading in various directions, but it does not often attain the heights of Blechnum filiforme.

The thick-leaved Phymatosorus diversifolius, with its stout, grey-green, black-flecked stems, is better known to most people. It ascends to higher altitudes than the species so far considered and also reaches the Auckland Islands to the south of New Zealand. It differs too in often preferring to climb inclined trunks and inclined or horizontal branches, so it is most common on trees such as mahoe, tree Fuchsia and kamahi, all of which have short trunks and many spreading branches. This fern may extend along all the branches and eventually into the crown of such trees. The stems branch freely and often rather untidily on their supports, sometimes curving completely around them. Where Phymatosorus diversifolius grows on the upper sides of more or less horizontal branches, quite a thick layer of humus builds up beneath its stems.

As the name of this species indicates, it has a range of leaf forms similar to P. scandens. On a tree with a heavy growth of the fern, the large, shiny, bright green leaves are rather widely spaced and deeply incised into narrow segments with an abundance of sporangia beneath, aggregated into distinctive orange spots or sori. Young plants establishing themselves in moss on trunk bases have narrow, undivided sterile leaves. Phymatosorus diversifolius also grows on the ground, most abundantly on rocky slopes. In rocky, exposed places the narrow, undivided leaves may persist, but in these circumstances they bear sporangia.

A third species of Phymatosorus—P. novae-zelandiae — is found in montane forests throughout the North Island, but is absent from the South Island. With its stout rhizomes it is similar to P. diversifolius, but the rhizomes are densely covered with straw-coloured scales and the leaves are generally larger with more numerous, narrower and longer lateral segments. It appears that there are no marked variations in leaf form in this species.

Rumohra adiantiformis ranges throughout New Zealand in lowland to montane forests and is most common as a climber on tree fern trunks. The much divided leaves have a leathery texture and bear conspicuous black sori. There is a modest increase in the size of leaves with increasing height.

Filmy ferns may be common as climbers in high rainfall areas. In some cases the fronds are very small and delicate and grow intermingled with mosses, but some species — Hymenophyllum dilatation, H. scabrum, H. sanguinolentum and several others — have relatively large leaves which, Holloway³⁵ notes, increase in size with increasing height above the ground. Holloway suggests that the increased leaf areas enable more effective absorption of water by the thin leaves in the drier tree trunk habitat. The kidney fern (Trichomanes reniforme) is perhaps our most unusual filmy fern. Its leaves are undivided and, as both common and botanical names indicate, kidney-shaped. This fern usually grows for only a short distance up tree trunks, but can climb much higher in moist situations. A strange case is the densely hairy Hymenophyllum malingii, which climbs on the dead trunks of trees, particularly mountain cedar (Libocedrus bidwillii). The climbing species of filmy fern range throughout the country.

Six of the climbing ferns considered here are restricted to New Zealand. The ranges of others are:

Phymatosorus diversifolius: Australia, Tasmania, tropical Polynesia.

P. scandens: Australia, Norfolk Island.

Arthropteris tenella: Australia, Norfolk Island, New Caledonia.

Rumohra adiantiformis: South temperate zone, tropical Polynesia, tropical America.