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Forest Vines to Snow Tussocks: The Story of New Zealand Plants


page 45

Woody and herbaceous vines, vascular epiphytes or 'perching plants', and vascular parasites and saprophytes are abundant and distinctive features of tropical rain forests.21 The stems of the vines climb their supports by a variety of means, including twining of the stems, tendrils, hooks and attaching roots. The epiphytes range from herbaceous plants to large trees. Among the former are nest epiphytes, with their large leaf rosettes, and an abundance of orchids, and among the latter are the 'strangling' epiphytes, including many species of fig (Ficus). The parasites attack stems or roots and may be without chlorophyll and completely parasitic or with chlorophyll and so able to manufacture some of their food requirements. Saprophytes are devoid of chlorophyll and are thought to derive their energy requirements from decaying organic material, particularly leaf litter, on the forest floor.

Surprisingly, in view of our temperate latitudes, a comparable range of vines and epiphytes are equally conspicuous in the New Zealand conifer broadleaf forest, but these have received little attention in books on New Zealand forest plants for the general reader. This partial neglect is perhaps understandable, as it is not easy to get close to the foliage, flowers and fruits of many of these plants, particularly where they occur high in the branches of tall trees. Binoculars help, but few botanists are as intrepid as J. L. Harrison-Smith,32 who spent many hours 'wandering about' among the branches of giant kauris recording epiphytes. In his own words: 'In order to catalogue the plants the trees were climbed. Ordinary gum collectors' climbing gear (spiked boots and climbing hooks) were used. Descent was accomplished with a "bo 'sun's chair" suspended from a rope. It was then possible to examine the trunk and any isolated branches on the way down.' Fortunately it is possible to reach most vines and epiphytes without taking such risks. Some species grow low on the trunks of trees and so are readily accessible, but even page 46those normally restricted to tree crowns may descend to lower levels in well-lit situations and, in the normal course of events, trees are blown or fall over (Fig. 26) and then a full range of high epiphytes and vines, albeit somewhat damaged, can be examined.

Not infrequently the categories of vines, epiphytes and parasites are confused, so that if it is stated that a plant 'grows epiphytically on trees', further enquiry is often necessary to determine the precise mode of growth of the species in question. It is true that the word 'epiphyte', meaning 'a plant that grows on other plants', fits all three categories, but as in other respects their life styles are quite distinct, this term should be restricted to plants which germinate and establish themselves on the trunk and branch surfaces of trees. Vines, by contrast, establish themselves on the ground, then grow up the trees. Some parasites are similar to epiphytes in that their seeds germinate on trunks and branches, but they differ markedly in having special root-like organs that penetrate the living tissues of their host and draw water and nutrients from them.