Tuatara: Volume 28, Issue 2, February 1986
The Vines, Epiphytes and Parasites of new Zealand Forests1
The Vines, Epiphytes and Parasites of new Zealand Forests1
Keywords: Climbing plant, epiphyte, forest, liane, New Zealand, parasite, saprophyte.
The specialised forest growth forms are defined.
The vines are divided into subcanopy herbaceous species (ferns) climbing by roots and woody canopy lianes climbing by roots, twining stems, twining leaf petioles, tendrils, hooks or scrambling stems.
For epiphytes the primary categories are shade epiphytes growing low on trunks and sun epiphytes in tree crowns. The latter are subdivided according to their forms or locations — mat, nest, pendent, small shrub, large shrub, tree or “strangler”, on tree ferns, on leaves (epiphyllae).
Parasites attached to roots or branches are reviewed. Our few saprophytes are described and their life style compared with that of parasites.
Woody and herbaceous vines and vascular epiphytes or “perching plants” are abundant and distinctive features of tropical rain forests. Surprisingly, in view of our temperate latitudes, a comparable range of vines and epiphytes is equally conspicuous in the New Zealand conifer broadleaf forest2 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, 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 those normally restricted to tree crowns may descend to lower levels in well-lit situations. Also, in the normal course of events, trees are blown or fall over and then a full range of high epiphytes and vines, albeit somewhat damaged, can be examined.page 44
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 “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 that germinate and establish on the trunk and branch surfaces of trees. Vines by contrast establish on the ground, then grow up the trees, and, although some parasites are similar to epiphytes, in that their seeds germinate on trunks and branches, they differ markedly in having special root-like organs (haustoria) that penetrate the living tissues of their host and draw water and nutrients from them.
(a) 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 with increasing height above the ground. The best known example of this is Blechnum filiforme a common plant in lowland forest as far south as the northern South Island. (Fig. 1). Blechnum filiforme is often abundant on the forest floor where it spreads by slender stems. In this situation the leaves are only about 10 cm long and once-pinnate with small oblong to almost round leaflets. Where stems grow up tree trunks, as they frequently do, the leaves produced are progressively larger, until several metres above the ground they attain a maximum length of almost 35 cm and have long, narrow, pointed leaflets up to 10 cm long. It is among these largest leaves that the fertile, spore-bearing fronds, with their almost thread-like segments, 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 metres above the ground.
Arthropteris tenella 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 5-10cm long, once-pinnate and are often rather peculiar in appearance — the few pairs of lateral leaflets are small and almost circular, the terminal leaflet is much larger and longer, narrowing to a point. Fully adult leaves are 30 or more centimetres long with many pairs of narrow, wavy-margined leaflets up to 8cm long.
The light green, thin-leaved Phymatosorus scandens also shows a trend from juvenile to adult leaves with increasing height, but in this 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. This species often occurs with Blechnum filiforme in lowland forests, sometimes on the same tree, but has a wider range 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 doesn't often attain the heights of Blechnum filiforme.
Legend for Fig. 1 should read:
Upper right: Leaf from near ground on a tree trunk. Left: Leaf 3 metres above the ground.
Below right: Fertile leaf.
Fig 1. Blechnum filiforme. Upper left: Leaf from near the ground on a tree trunk. Right: Leaf 3 metres above the ground. Below: Fertile leaf. Photo: M. D. King.
As the name of the species indicates it has a similar range of leaf forms to P. scandens. On a tree with a heavy growth of the fern the large, shiny, bright-green leaves are rather widely spaced and are deeply incised into narrow segments with an abundance of sporangia beneath aggregated into distinctive orange spots or sori. Young plants establishing 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 thick, leaves and stout stem it is similar to P. diversifolius, but the stems 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 the 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 sori. There is a modest increase in size of leaves with increasing height.
Particularly in high rainfall areas filmy ferns may be common as climbers. In some cases the fronds are very small and delicate and grow intermingled with mosses, but some species — Hymenophyllum dilatatum, H. scabrum, H. sanguinolentum — have relatively large leaves which, Holloway notes, increase in size with increasing height above the ground. Holloway suggests that the increased leaf areas in this case 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. The leaves are undivided and, as both common and botanical names indicate, kidney-shaped. Usually this fern 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 the 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)
(b) Canopy climbers
Vines whose foliage eventually spreads into the canopy of the forest are usually woody and are often referred to as lianes. 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.
Most prominent here are the climbing ratas, currently included in the genus Metrosideros. They are able to grow up quite large trunks and are perhaps most abundant on conifers and northern rata. The climbing stems are usually quite slender and the leaves, forming a close mosaic on the tree trunk, 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 at lower levels where light is adequate, 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. 2). Metrosideros fulgens and M. perforata form the largest stems, sometimes up to 15 or more cm 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. The former is commonest in kauri forests, has the largest leaves of the group and small, white flowers. The latter is much more colourful with masses of larger, 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 south west South Island and the last 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 encountered. M. colensoi reaches the northern South Island, but is more localised in its occurrence favouring forests on fertile soils such as those on 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 wide-ranging 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 the length of its flowering season — the first flowers may appear in late summer and flowering continues through the winter into early spring.
It has been said that New Zealand is the only place where climbing species of Metrosideros occur, but in fact there are climbers related to ours in New Guinea and the Philippines.
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 out-lying New Zealand species would be of reduced form and perhaps rare, but in fact it compares with the largest and most robust tropical species and is abundant in lowland, especially swampy forests as far south as the south west of the South Island. Tree trunks are often completely obscured by the foliage of kiekie, which can extend into the highest crowns 30 or more metres 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, 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
Fig 2. The cable-like stems of Metrosideros perforata on a rimu (Dacrydium cupressinum). A young plant of the climber can be discerned on the left side of the rimu trunk. Photo: M. D. King.
Fig 3. An entanglement of supplejack (Ripogonum scandens) Photo: M. D. King.
Undoubtedly, supplejack (Ripogonum scandens), which ranges throughout the country, is the most familiar twiner in New Zealand forests 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. 3). 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 bear pairs of long, narrow, often twisted scales in the 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.
Supplejack mostly climbs fairly slender supports, but can also twine around quite large trunks, the record being a 1.5 m diameter kohe-kohe. When a climbing stem reaches the forest canopy, lateral climbing stems arise from its upper parts and eventually these 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 reaches the crowns of taller trees deeper in the forest by spreading from lower to higher levels in the forest canopy.
In this species there is a very marked difference in size and shape between juvenile and adult leaves. The seedlings establish 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 base and tip and rotund 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.3 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.
Seedlings, rotating 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 up to 25 cm in diameter.page 51
Parsonsia capsularis has small flowers of a different form to those of P. heterophylla, but the adult leaves of some variants 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 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 red (P. capsularis only). The fruits are pod-like, hang downwards and split open to release numerous seeds, each with a dense tuft of hairs for wind dispersal.
It has been suggested that the distinctive juvenile forms of our Parsonsias are peculiar to New Zealand, but in fact the phenomenon is also found in species in eastern Australia and New Caledonia. The genus ranges from tropical Asia to the Pacific.
Two of the New Zealand species of Muehlenbeckia are common twining lianes throughout New Zealand in lowland to montane forests. Both are deciduous, M. australis is the larger species and its seedlings are often abundant on the forest floor in both shady and well-lit places, but mature plants are most commonly found at forest margins or in regenerating forest. Young stems bend to the ground if they don't find support, branch, and 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.
By climbing up smaller trees Muehlenbeckia australis may extend into the crowns of tall trees 30 metres or more above the ground. A distinctive feature of this vine is the formation of firm cane-like “searcher shoots” during the autumn from any part of the stem sysfem. 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 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. Particularly in second growth forest there sometimes seems to be more of the draping foliage of the Muehlenbeckia 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, or oval and sometimes fiddle-shaped.
Muehlenbeckia complexa is similar in its growth habit to M. australis, but is smaller in all respects and grows on shrubs and 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.
Muehlenbeckia complexa is endemic and M. australis grows on Norfolk Island. The genus also occurs in Australia and southern South America.
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.
Lygodium articulatum (Mangemange) belongs to a largely tropical genus of ferns unique for their ability to climb by twining, although in this case it is not the stems that twine, but the axes of compound leaves that 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 is common there 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, near the ground in well-lit places or on the forest roof. Compound page 52 leaflets arise 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 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 which in subsequent leaves become broader and deeply lobed and gradually trend to the adult form where lighting is adequate. Similar juvenile leaves have been reported for Clematis species in eastern Australia. Seedlings rotate in 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 downwards 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 a petiole in contact with the support enlarges and becomes strengthened. Clearly the leaves cannot attach to large supports, so where a large stem, up to 10 cm in diameter, of Clematis paniculata ascends to a tree crown 10 metres 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, 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 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 — that 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 that climbs by tendrils. This is the native passion vine — Passiflora tetrandra, which ranges through the North Island and 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 cultivated species and less elaborate in their form, but the fruit compensates for this, being bright orange, 2-3 cm in diameter and it is greatly sought after by birds.page 53
The tendrils arise in leaf axils and are considered to be modified inflorescences. They are at first erect then bend downwards and 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 widespread genus in temperate regions and the montane tropics, which includes the familiar blackberry and raspberry. 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 coriaceous leaflets and the undersides of the petioles and leaflet midribs, as well as the stems at times, are beset with backwardly curving hooks or prickles, which effectively prevent the stems from slipping back from any position attained. This tenacity earned for the New Zealand plants the name of “bush lawyer” in colonial times, a perhaps unwarranted slur on the legal profession of the day. In fact the “lawyers” are the only plants in New Zealand forests that are prickly, which contrasts with the rain forests of Queensland and south east Asia where many spiny climbers are unpleasantly in evidence. Probably the original lack of browsing mammals in New Zealand is the 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 ascents in a similar way, but the presence of hooks enables 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.
Young plants, the first leaves of which are simple, may have quite stout stems 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 and 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. On woody stems looped on the forest floor and those extending to the forest roof “searcher shoots” are frequently produced, those arising near the ground being able to stand without support for one to several metres. Thus the searcher shoots are 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 and narrow, sharply toothed leaflets. The adult stems may be up to 17 cm in diameter and the foliage can reach to 15 or more metres above the ground.
Rubus schmidelioides has stems up to 10 cm in diameter. Its leaflets are similar in shape to those of R. cissoides but generally smaller with blunt teeth and a dense covering of whitish hairs beneath.
Rubus australis is most common in swamp forest and is sometimes referred to as “swamp lawyer”. The leaflets are short and fairly broad and sometimes almost circular. In this species there is a distinct juvenile form, which spreads and roots widely over the forest floor and bears leaves with small, membranous, more or less round leaflets with reddish coloured veins. At the adult stage this species can reach for 10 metres or more into tree crowns with stems several centimetres in diameter.
Rubus squarrosus is perhaps the most remarkable, as in open situations and on shrubs the leaflet blades are not developed and the leaves consist of rather elongated page 54 petioles and the almost threadlike midribs of the leaflets, all beset with yellow prickles. 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.
(c) Low Climbers of Forest Margins and Shrublands
Some low climbers of more open habitats — Parsonsia capsularis, Muehlenbeckia complexa, Clematis (several species) — have already been considered in association with their higher climbing relatives. Other small but specialised non-endemic vines of northern coasts are: Ipomaea palmata and Calystegia tuguriorum (twining stems — Convolvulus family); Sicyos angulata (tendrils—cucumber family).
The remaining species are mostly unspecialised “scramblers” as defined in the last section in the discussion of hook climbers. They grow through shrubs and small trees at forest margins or in shrub communities in drier eastern localities. The species in this group are: Fuchsia perscandens; Brachyglottis (Senecio) sciadophilus and Helichrysum dimorphum of the Compositae or daisy family; Scandia geniculata of the Umbelliferae or carrot family, perhaps the only climbing member of this family; Carmichaelia kirkii, one of the leafless brooms; and an undescribed species of Coprosma.
One of our species of Lycopodium, the attractive trailing L. volubile, can also be a scrambling climber over shrubs. This species ranges to the tropical Pacific and south east Asia and in the latter region is recorded as sometimes extending into tree crowns.
(d) Vines growing as Shrubs in open situations
A number of the vines in the absence of support can grow as shrubs in open situations. This is particularly the case with the small, unspecialised scrambling species, as well as the small twiners Muehlenbeckia complexa and Parsonsia capsularis, which are able to make an easy transition from well-lit forest margin and shrubby habitats to completely open sites. As shrubs these species often have a ball-like form with a profusion of slender, entangled stems.
Some of the taller, more specialised forest vines may also grow as shrubs. Rubus squarrosus is particularly striking in this role as it is entirely leafless and presents a forbidding mass of slender stems and petioles beset with yellow prickles.
Several of the climbing ratas (Metrosideros) too, can be encountered as shrubs, M. perforata in particular having a dense, billowy form, which gives no hint of any ability to climb.
Such dual roles are not peculiar to New Zealand vines, but have also been observed in a number of tropical lianes.
Sharing a need for much brighter light than is available on the floor of a closed forest the majority of species of epiphytes, vines and parasites grow high in tree crowns. In this situation epiphytes alone face special problems. Vines are able to obtain soil water and mineral nutrients via their stems; parasites can tap the supplies drawn up by their host trees; but epiphytes either have no connection with the ground throughout their lives or send roots down to it only after a period of some years. Soil does not form easily on trunks and branches and as they are sunnier, windier and better drained than the ground, they suffer both more frequent and more severe droughts. In response to these stressful conditions many epiphytes have evolved modifications enabling them to store water and to reduce its loss by evaporation. Water can be stored internally in special cells, whose presence confers fleshiness on the organs concerned, or externally in cavities formed by appropriately shaped and arranged leaves. Some epiphytes can get by with a minimum of mineral nutrients and need little or no soil, others build up considerable quantities of dark humus largely from the decay of their own old leaves and roots with a varying contribution of bark flakes and leaves from surrounding trees. Many other epiphytes unable to form soil themselves take advantage of those that can.page 55
Now that we have defined the epiphyte category how rigorously do we interpret the definition in deciding whether or not a particular species should be included? Certainly not so rigorously that we exclude those species which, although normally epiphytic, are sometimes to be found on sunny, rock outcrops that provide conditions similar to those of tree tops. In fact, it might well be that there are no epiphytes, even those of tropical forests, which are unable to grow on the ground in suitable circumstances.
Going to the other extreme, should we include species that are normally terrestrial, but can occasionally grow on trees? In this case the answer is “no” as apart from reservations about stretching the definition so far, the number of species involved would be inconveniently large. In certain circumstances almost any plant is able to grow as an epiphyte. For example, in forests of high rainfall regions, particularly where frequent mists maintain high atmospheric humidity, seeds germinate just as readily on moist, moss and lichen covered trunks and branches as on the ground. A notable example of chance epiphytism in these circumstances in New Zealand, is an occasional silver beech (Nothofagus menziesii) growing on a tree of the same species. Even in forests of average rainfall and atmospheric humidity the branch systems of large long lived trees, such as the kauri, are available as habitats for so many centuries that quite unlikely species can sometimes be found as epiphytes on them. The intrepid Harrison-Smith found a 3 metre kauri growing on a kauri, as well as a few to several examples of other conifers—rimu, totara, kahikatea—and also several angiosperm trees. In most cases the occasional epiphytic plants of otherwise terrestrial trees and shrubs are small and do not grow on to reproductive maturity.
Lichens, often followed by mosses, are generally the first epiphytes on trees in both temperate and tropical regions. In New Zealand small filmy ferns are often associated with the mosses. The thin layer of soil that these small epiphytes form is important for the establishment of most of the vascular epiphytes, which are the concern of this section.
(a) Shade Epiphytes
These do not require a very high level of light and as epiphytes they mostly grow low on tree trunks where they escape the shading of the larger plants of the forest floor.
Five small species of fern and two flowering plants occupy this station in New Zealand although they are also to be found on rocks. Of the ferns three are species of Grammitis characterised by tufts of narrow simple leaves arising from short stems. G. pseudociliata differs from G. billardieri and G. magellanica ssp. nothofageti in having an abundance of reddish hairs on its leaves. G. pseudociliata is concentrated in the North Island, G. billardieri and G. magellanica extend throughout the country and the last also occurs in southeast Australia.
Ctenopteris heterophylla occurs throughout the country as well as in the subantarctic islands and south east Australia. Its habit is similar to that of the Grammitis species, but the leaves are somewhat larger and once-pinnate with the leaflets toothed.
Anarthropteris lanceolata is found in the North Island and near the northern shores of the South Island, as an epiphyte or on rocks. It is also said to occur in Vanuatu. The leaves are very similar in shape to those of Grammitis but longer. The stems are short and produce masses of slender furry roots some of which can give rise to new tufts of leaves.
These four epiphytic ferns are related to the climbing Phymatosorus species and have similar prominent, rounded, brown to orange sori.
The two flowering low epiphytes are both species of Peperomia, a large genus of small succulent plants in tropical and subtropical regions. As epiphytes they grow mostly near the coast in the northern half of the North Island.
P. tetraphylla ranges from the East Cape district through to the Bay of Plenty. It has leaves in whorls of four as its name indicates. The same species is also found in Australia and Polynesia. P. urvilleana, with leaves borne singly, is found throughout page 56 the North Island and near the northern shores of the South Island, but is less common in the southern part of its range and there grows mostly on rocks. It is also in Norfolk and Lord Howe Islands.
(b) Sun Epiphytes
These are more numerous and diverse than the shade epiphytes and can be grouped into several growth forms.
These form mats or patches mostly on inclined to horizontal branches, and comprise three orchids and one fern which range throughout the country. These mat epiphytes may establish directly on bare bark, particularly if it is rough and fissured, but may also avail themselves of moss cushions. The one fern is Pyrrosia serpens belonging to a genus of epiphytes centred in tropical Asia. Our species is also found in Australia and the islands of Polynesia. Pyrrosia often establishes directly on bare bark and has slender, freely branching stems which form a complete network over sunny branches. The leaves are simple and smooth-margined, varying from almost round to long and narrow. They have a fleshy texture and a dense felt of buff coloured hairs beneath, which presumably restrict loss of water. Pyrrosia also grows on the trunks of trees in the open and on rocks. It can be quite abundant on introduced trees as well, particularly Cupressus macrocarpa.
The epiphytic orchids belong or are closely related to large tropical genera and can be regarded as outliers reduced in both leaf and flower size. They all have specialised roots, which as well as serving for attachment, also efficiently absorb and store water in a special outer layer of dead cells known as the velamen.
Drymoanthus adversus, often attached to quite smooth bark, is unlike the other species in that it has a short stem, which does not grow along the bark surface. The roots arising at the base of the tuft of leaves are particularly conspicuous as they spread out “like the rays of a spider's web” for a considerable distance, often encountering the roots of other plants of the same species. Drymoanthus includes our species, another in east Australia and a third in New Caledonia, but there is some doubt whether it should be separated from the Asian and Australian genus Sarcochilus. Our two species of Bulophyllum, although small, form quite dense patches with their branching stems. In common with their many tropical relatives, each of their stem segments swells at the end into a water-storing “pseudobulb” with a single leaf arising from the top. The stalk bearing the small flower or flowers arises from below the pseudobulb. Bulbophyllum pygmaeum is the smaller species with leaves about a centimetre long but it forms larger patches than those of B. tuberculatum. The leaves of B. tuberculatum are several times longer, but this species is less frequently seen and is not known further south than the north coast of the South Island.
Much more evident to the casual observer are the massive nest epiphytes perched high in tree crowns (Fig. 4). In New Zealand there are three long and narrow-leaved species belonging to two closely related genera of the lily family — Collospermum hastatum, C. microspermum and Astelia solandri. Two other species of Collospermum are found outside New Zealand, one in each of Fiji and Samoa, and both are epiphytes. In the much larger and more widespread mostly southern hemisphere Astelia, however, only a few species are consistently epiphytic. The others in New Zealand are found in a variety of habitats—coastal cliffs, swamps, forest floors, alpine tussock grassland and a few reduced turf-forming species in alpine bogs.
Fig 4. Nests of Collospermum hastatum with fronds of Asplenium polyodon hanging below them. Photo: M. D. King.
Astelia solandri is more shade tolerant than the Collospermums and so is often found below them in the lower branches and on the upper trunks of trees. The silvery green leaves are in three ranks and are one or two metres long, but only 2-3 cm wide. Their bases are tightly folded forming a narrow ridge at the back. Astelia solandri is found in lowland forests throughout the North Island, near the northern coast and down the western side of the South Island at about 44 degrees S.
Collospermum hastatum accompanies Astelia solandri through the North Island and to about 42 degrees 30′ in the South Island. It has fan-like arrangements of black-based leaves (Fig. 4) which are somewhat shorter and much broader than those of Astelia solandri. The leaf bases are strongly rounded and enclose spaces or “tanks” which become filled with water when it rains. Often sufficient water is contained by the tanks to provide a shower bath for the unwary when a fallen collospermum nest is lifted and tilted. A species of mosquito has been described whose larvae always develop in the water stored by Collospermum hastatum but this is a very modest fauna compared with the many insects and even frogs inhabiting the “tanks” of the tropical American epiphytes of the Bromeliaceae (pineapple family). The water stored by C. hastatum is partly absorbed by roots that grow into the tanks, but the suggestion that it is also absorbed through the embedded multicellular bases of overlapping scales has not been confirmed. In some tropical bromeliads all of the stored water is absorbed through the bases of similar scales.
Collospermum microspermum is equally specialised but its leaves are as narrow as those of Astelia solandri and dark-brown rather than black at the base. Unlike C. hastatum its leaves have a fringe of marginal hairs. C. microspermum is restricted to the North Island and replaces C. hastatum in forests above about 300m.
The collospermums are the only known tank epiphytes outside the family Bromeliaceae, but as they very efficiently form soil, they are also nest epiphytes.
Four New Zealand-wide pteridophyte species often grow as epiphytes with their roots or rhizomes embedded in the soil of epiphyte nests. Though they occur elsewhere as well it is in such sites that their growth is most vigorous and their pendulous stems or leaves attain their maximum length. Of the four, Lycopodium varium is the most impressive, its slender stems sometimes forming huge masses up to 1½ metres long below collospermum nests. The stems branch repeatedly by equal forkings or dichotomies, so that a dense, but well balanced mass is formed. It is almost constantly in motion as even the lightest breeze can set the tassels swaying. In their upper parts the stems are clothed with small spreading leaves, which grade into small, close set scales enclosing the sporangia towards the branch tips. Lycopodium varium is restricted to New Zealand, but there are related species in tropical forests.
Fig 5. Griselinia lucida epiphytic on a kahikatea (Dacrycarpus dacrydioides). The foliage of the Griselinia is below the Collospermum nest and its main descending root is to the left of the kahikatea trunk. Photo: M. D. King.
Tmesipteris, a genus restricted to the south west Pacific, is sometimes referred to as a “living fossil” as it is considered to be one of the most primitive genera of land plants. One of the highlights for botanical visitors to New Zealand is to see a living plant of this genus.
Tmesipteris elongata subspecies robusta has been observed growing from Collospermum clumps at a number of localities through the North Island, but not yet in the South Island. Its stems, with their small, simple leaves, are unusually long for a Tmesipteris and dichotomize freely. Other species of Tmesipteris rarely branch. The smaller Tmesipteris tannesis may also hang from tree trunks or branches.
Three orchid species can also be included as pendent epiphytes. The two Earinas belong to a small genus with other species in New Caledonia and Polynesia, but is considered to be closely related to the large genus Epidendrum of tropical America. Both species have spreading stems and can sometimes extend for several metres along branches. The stems bearing the leaves droop downwards and can be 30 or more centimetres long. The leaves are in two rows and more or less in one plane; those of E. mucronata are narrow, thin and quite grasslike while those of E. autumnalis are broader and thicker in keeping with the more robust nature of the plant as a whole. Both species form terminal sprays of small flowers, E. amucronata in the spring and E. autumnalis in the autumn. The flower clusters of the former hang down and are yellowish orange, those of the latter turn upwards and are waxy white with a strong spicy perfume.
Our sole species of the large tropical genus Dendrobium — D. cunninghamii — is the largest of our epiphytic orchids, its freely branching stems and narrow leaves forming feathery drooping masses. The stems are polished, often bright yellow and very bamboo-like in appearance. The white, reddish centred flowers are scattered and while modest by tropical standards, are at 2 to 2½ centimetres diameter, the largest among our epiphytic orchids.
Small shrub epiphytes
The two species of Pittosporum and one species each of Senecio and Coprosma in this category are usually not more than a metre high when growing as epiphytes, but may attain small-tree size on the ground. All are endemic to New Zealand.
Pittosporum cornifolium is found throughout the North Island and although it is quite a common plant, many people are unaware of its existence perched as it is inconspicuously in tree crowns. The stems of this plant are spindly and they often hang down below the branches. The leaves are thin but firm with prominent veins and the flowers are small and yellowish red. The round, woody seed capsules are a surprise. When they open they reveal a bright red lining and shiny black seed embedded in a sticky bright yellow fluid.
Pittosporum kirkii has a more restricted range, not being found further south than the central North Island. It has a more erect growth habit with thicker stems and longer, thicker almost fleshy leaves with obscure veins. The flowers are bright yellow and the capsules are unusually large, up to 4 cm long, and are flattened and pod-like. Kirk, after whom the species is named, states that the “valves contract in a curious manner when the capsule bursts”. The capsule is apparently not so colourful as that of P. cornifolium but is described as having an orange lining.
Senecio kirkii is found in lowland forests throughout the North Island but has not been recorded from the South Island. Its growth form has been described as “candelabralike”. The leaves are soft and somewhat fleshy and the flowers, up to 5 cm diameter, are pure white and crowded into dense heads.
The thick and shiny-leaved karamu (Coprosma lucida) is best known as a ground plant in shrubby early forest regrowth on drier sites, but is also reasonably common as an epiphyte in asteliad nests. The species is found throughout the coountry but presumably is common as an epiphyte only within the range of nest epiphytes.
Large shrub epiphytes
As well as being larger than those of the preceding category, these also eventually send a root to the ground and so overcome the water supply and soil nutrient problem.
Puka (Griselinia lucida) is the most notable in this category, its large, dark-green shining leaves usually contrasting so strongly with the foliage of the supporting tree that it stands out even to the casual observer (Fig. 5).
Puka is distributed in lowland forests throughout the North and South Islands, but is more common in the north. Its seedlings generally establish in asteliad nests situated at branch forks and its roots ramify through the humic soil. After a few years a strong root begins to grow down the trunk of the supporting tree towards the ground. This root and its branches are closely appressed to the bark of the trunk, frequently growing into crevices and behind bark flakes. The root tips are white and smooth, but from a short distance behind them, the root surfaces are densely clothed with short root hairs. These apparently persist until cork formation commences, as they are undiminished up to a metre from the growing points. Where the roots are in contact with the trunk, they are anchored by the root hairs and the union is sometimes so complete that when the roots are pulled away they either remove portions of bark or leave strips of their own tissue behind.
When the root tips reach the ground generally one main vertical root enlarges greatly until it attains a diameter of ten or more centimetres. This main root usually has a few major branches near the ground and the whole system has a very distinctive appearance resulting from the more or less continuous and pronounced longitudinal grooves and ridges of the bark. In its upper parts the main root gives rise to slender horizontal, girdling roots, which often encircle the trunk or the supporting tree many times and so ensure that the puka will not be dislodged even by the strongest gale.
Two other species, Griselinia littoralis and Pseudopanax colensoi, although mostly terrestrial, can grow as epiphytes in the moist montane or higher latitude forests that they favour. When growing as epiphytes they are generally beyond the altitudinal or latitudinal range of asteliad nests and so establish in the moss and lichen cushions of branch forks. Like the puka they eventually send a root or roots to the ground.
Griselinia littoralis (broadleaf) is the only other species of its genus in New Zealand. Its leaves are smaller than those of puka, yellowish green, and symmetrical or only slightly asymmetrical at the base. In puka the leaf base is very asymmetrical as the two parts of the leaf divided by the midrib are of quite different lengths. Broadleaf has been observed as an epiphyte on a variety of trees. Its descending roots are often more massive than those of puka, but they are not grooved. The species ranges throughout New Zealand including Stewart Island. Beyond New Zealand Griselinia is only found in Chile, where there are five species, at least some of which are epiphytes.
Pseudopanax colensoi (mountain five finger) also has a wide range, but is absent north of 36 degrees S and from Stewart Island. I have observed it growing as an epiphyte on Libocedrus bidwillii (kaikawaka) on Mt. Egmont and on Podocarpus dacrydioides (kahikatea) on the volcanic plateau near Mt. Ruapehu.
The descending roots of puka and mountain five finger seem too slender in relation to their height to stand alone when the supporting trees die, but this may be possible for the more massive roots of the broadleaf.
Tree or Strangling Epiphytes
Fig 6. Northern rata (Metrosideros robusta) with a “trunk” of coalesced roots. The broken top of the trunk of the original supporting tree is indicated by an arrow. Photo: M. D. King.
Fig 7. Five finger (Pseudopanax arboreus) as an epiphyte on a tree fern trunk (Cyathea dealbata) Two fronds of the tree fern can be seen to the right of its trunk at the top of the photo. Photo: M D. King.
With the development of such a massive root system, when the supporting tree eventually dies the northern rata is able to stand alone on its “pseudo-trunk” (Fig. 6). If the support was an emergent then the rata now replaces it in that role.
The northern rata and tropical epiphytic trees of similar habit, are often referred to as “stranglers”. This implies that these epiphytes kill the supporting trees by compressing their trunks with a complete or partial network of roots. Popular writers on New Zealand plants have taken enthusiastically to this idea describing the northern rata variously as a “predatory gangster”, “forest bandit” or “notorious strangler” which “crushes”, “smothers”, “stifles”, or “squeezes” the supporting tree in an “iron” “deadly” or “fatal embrace”.
Partly as a reaction to these verbal flights, some botanists in recent times have tended to take a contrary view. They point out that the light demanding northern rata generally establishes in the well-lit crowns of mature trees so that, by the time the former is large enough to stand alone, the supporting tree might well have died of old age. It does seem, however, that the northern rata must have some deleterious effect on the supporting tree by partial overshading, root competition, and perhaps in cases where the supporting trunk enlarges within a well developed rata root cage, by some restriction in the movement of water and dissolved nutrients.
Recently a distinctive new tree species of Metrosideros has been discovered. It is restricted to a few forest patches near North Cape and has a similar epiphytic habit to northern rata.
Southern rata (Metrosideros umbellata) is rare and localised in the North Island, but quite common in montane and higher latitude lowland forests in the west of the South Island. It is mostly terrestrial, but has been observed growing as a “strangling” epiphyte at several places.
Similar Metrosideros epiphytes are known in New Caledonia, Fiji and Hawaii.
Epiphytes on Tree Ferns
These are considered separately, as tree ferns provide a substrate rather different from the bark of ordinary trees. To begin with tree ferns do not branch, so only the trunk is available for colonisation. Secondly, the trunks are built up from persistent leaf bases, which provide a variety of surfaces according to the species, but none is quite like bark. Also the large crowns of leaves cast considerable shade so any epiphytes need to be shade tolerant at least when young.
The different species of tree fern vary in their suitability for epiphytes. In our largest and most handsome species, the mamaku (Cyathea medullaris) the leaf bases decay down to hard leafscars which collectively form an armour-like surface unsuitable for epiphytes. In the lower parts of the trunk masses of slender roots grow out adding considerably to the diameter of the trunk, but these too form a hard dry surface.
In the ponga or silver tree fern (Cyathea dealbata) the leaf bases decay more gradually and do not form well-defined scars. As a consequence soil forms readily in the interstices and a variety of epiphytes are able to establish. Wheki (Dicksonia squarrosa), D. fibrosa and Cyathea smithii have a similar trunk to that of the ponga, but in the last two epiphytes are discouraged in the upper part of the trunk by the persistence of the old leaves as a “skirt”. Thus epiphytes are most commonly found on the trunks of ponga and wheki.page 65
In moist situations lichens, mosses, liverworts and smaller and larger ferns may be abundant on tree fern trunks. Climbing ratas and other climbers may also be present as well as a range of seedlings of trees and shrubs which die before reaching maturity. Here we will consider only the consistent and specialised tree fern epiphytes. It is worth noting that the species concerned are mostly different from those occurring on ordinary trees.
(i) Herbaceous species
A Lycopodium is quite commonly encountered. It is smaller than Lycopodium varium on trees, and the leaves associated with the sporangia towards branch tips are often not reduced to scales. Some treat it as a distinct species, L. novaezelandiae, others regard it as a form of L. varium.
Asplenium flaccidum, common on trees, also inhabits tree fern trunks. Several species of Tmesipteris are largely restricted to such sites — T elongata subspecies elongata throughout and T. lanceolata and T. sigmatifolia in the northern North Island.
One shrub and one tree frequently, and several other species less commonly, play this role on tree ferns.
Five finger (Pseudopanax arboreus) is common as a terrestial plant in shrubby forest regrowth, but in more mature forest it can be surprisingly frequent as a tree fern epiphyte, mostly on the ponga, but also on wheki. The seedlings establish at the top of the trunk and being fairly light demanding, their leaves soon push between and above the fern fronds. The primary root begins to grow down to the ground, but soon gives off a branch root which grows horizontally around the trunk sometimes returning to and fusing with the vertical root. It is thus comparable with the girdling roots of the puka and northern rata. The vertical root eventually reaches the ground and sometimes branches to enclose the tree fern trunk in a network of roots in its lower part. In the meantime, the crown of the five finger has continued to branch and grow upward with the tree fern crown following behind it. (Fig. 7).
Less frequently Pseudopanax edgerleyi (raukawa) and Coprosma grandifolia adopt a similar life style.
Kamahi (Weinmannia racemosa), the main canopy dominant in many montane and higher latitude forests, also frequently begins its life as a tree fern epiphyte, particularly on wheki (Dicksonia squarrosa). In this case, the seedlings establish anywhere on the trunks but usually lower down than five finger. The kamahi sends a root to the ground, which branches several times, but it doesn't seem to form girdling roots. Instead it often sends a branch root vertically upwards within the tree fern trunk. The tree fern continues to grow for a time, but eventually breaks off above the junction with the kamahi leaving a stump. This stump can often still be discerned among the several spreading trunks of quite large kamahis. In the north of the North Island Weinmannia sylvicola and Ackama rosaefolia may also start their lives as low epiphytes on tree ferns.
Epiphytes growing on the ground
As had already been mentioned, epiphytes sometimes grow on the ground and in some circumstances may be important components of terrestrial communities. On Rangitoto Island for example, a volcanic cone only a few centuries old in Auckland harbour, the epiphytes northern rata (Metrosideros robusta)), puka (Griselinia lucida), Senecio kirkii, Astelia solandri) and Collespermum hastatum are common on dry sunny mounds of scoria. Pohutukawa (Metrosideros excelsa) is also present and it hybridizes freely with northern rata. Further to the south near Wellington there is a remarkable series of raised beaches and on rocky outcrops a number of normally epiphytic orchids are to be found — Earina autumnalis, E. mucronata, Dendrobium cunninghamii, and page 66 Bulbophyllum pygmaeum. Drymoanthus adversus was also recorded early this cenutry, but seems to have disappeared. The ferns Asplenium flaccidum and Pyrrosia serpens are also present.
Epiphytes growing on Leaves.
Epiphyllae as they are termed, are not so evident on the generally smaller leaves of the New Zealand rain forest as they are on the large leaves of the tropical rain forest. As in the tropics the plants concerned are filamentous algae, leafy liverworts and lichens.
One epiphyllous alga in New Zealand is commonly observed on the leaves of mahoe (Melicytus ramiflorus.) This is a species of Trentepohlia and it forms conspicuous reddish patches on old leaves of mahoe in autumm and winter.
Five epiphyllous species of liverwort each from a different genus, have been recorded in New Zealand. They are related to epiphyllae of the tropics and in New Zealand have been found mostly on fern leaves, but also on leaves of trees and shrubs including Pseudowintera(horopito).
Epiphyllous lichens were the subject of a detailed study by Allan at Kitchener Park, Feilding. They were found to be abundant on the leaves of the conifers totara (Podocarpus totara), matai P. spicatus and kahi katea (P. dacrydioides), on tawa (Beilschmiedia tawa), titoki (Alectryon excelsus), rama rama (Lophomyrtus bullata), the epiphytic orchid Earina mucronata and the liane Metrosideros colensoi.
The leaves of supplejack (Ripogonum scandens), the species of Coprosma, Pittosporum, Hoheria and puka (Griselinia lucida) were free of lichens.
Clearly much still remains to be learnt about leaf epiphytes in New Zealand.
Although all flowering plant parasites agree in having structures known as haustoria, which penetrate into the living tissues of the host, they differ quite widely in a number of other respects. Some are complete parasites as they lack chlorophyll and so are unable to utilise light energy to manufacture sugars. Others, having green leaves, make their own organic nutrients and derive from the host mostly water and inorganic nutrients.
Some parasites are attached to roots, others to trunks and branches.
Dactylanthus taylori is a complete parasite attached to the roots of a range of mostly small tree species in lowland to montane forest throughout the North Island. It is not readily observed as only the reddish-brown scaly inflorescences appear above the ground. The strange appearance of the flower heads apparently arising directly from the ground, led the Maoris to give the name Pua reinga (Flower of the Underworld) to this species.
Apparently the embryo root of a Dactylanthus seed penetrates the slender root of a suitable host, then gradually expands into a tuber-like structure which eventually surrounds the host root. The terminal portion of the latter then dies away. The “tuber” continues to enlarge and the end of the host root enlarges with it into a more or less disc-like form. Both can attain a diameter up to 30cm. The tuber has a flattened balllike shape and is covered with hard warty protuberances. Inflorescence buds originate between these, bearing male flowers on some plants, females on others. The flowers have a strong sweet perfume which is attractive to flies.
The junction between host and parasite is not flat, but formed into radiating grooves, v-shaped in section. It has been found that if the host/parasite mass is boiled the parasite can be removed exposing the expanded, fluted ends of the host roots. These “wooden roses”, as they are called, are prized as curios.
Dactylanthus is restricted to New Zealand but belongs to a largely tropical and subtropical family.page 67
Although Mida salicifolia is a root parasite on a wide range of trees including kauri, unlike Dactylanthus it does not advertise the fact. It is a small tree with narrow, green willow-like leaves in one variety and rather broader leaves in the other. It is found in lowland forests throughout the North Island, but becomes uncommon in the south of its range. The only other species of the genus is restricted to the Juan Fernandez Islands near Chile.
These all contain chlorophyll so are only partly dependent on their hosts for organic nutrients. All but one of the New Zealand parasites in this category belong to two largely tropical families — Viscaceae and Loranthaceae, collectively referred to as mistletoes. In the first the flowers are small and inconspicuous, in the second they are much larger and often brilliantly coloured.
Three small species of Korthalsella represent the Viscaceae. All have vestigial leaves and strongly jointed stems, which in K. lindsayi and K. clavata are strongly flattened and in K. salicornioides cylindrical. The latter is found throughout the country, the former two from the central North Island southwards and both parasitise a wide range of shrubs and small trees.
The New Zealand species in the family Loranthaceae are all green-leaved, freely branching shrubs up to one metre in diameter. Currently all these species are referred to a number of small genera, with one exception endemic to New Zealand, although formerly some were included in the tropical genera Elytranthe and Loranthus.
Tupeia antarctica is the only species of a genus restricted to New Zealand. Each plant is attached to a ball-like mass, which is a combination of the parasite haustorium and host tissues. Tupeia is found throughout the country and attacks a wide range of both native and introduced shrubs and small trees and occasionally other branch parasites.
Peraxilla colensoi and P. tetrapetala mostly parasitise. Nothofagus species in both islands. They have bright red flowers which form eye-catching patches of colour against the dark green beech foliage. The orange flowers of Alepis flavida mostly on beech trees are also very attractive. Trilepidea adamsii with reddish cream flowers is restricted to the northen Coromandel Peninsula and adjacent localities and was last recorded in the 1960's.
Ileostylus micranthus has small green flowers and yellow berries. It is widespread in New Zealand and Norfolk Island and has as hosts a range of shrubs, small trees and sometimes conifers both native and introduced.
The species of all these genera except Tupeia send out roots over the bark surface which form secondary haustoria at intervals. Ileostylus alone can form new leafy shoots from its roots.
The branch parasites have berries eaten by birds and the seeds are deposited on tree branches. The seeds are attached to bark by a sticky secretion.
Some branch parasites elsewhere have explosive fruits, which shoot the seeds for several metres. This has been observed in the New Zealand species of Korthalsella.
The remaining parasite in this category is Cassytha paniculata and it is quite different from the rest as it is a twining vine as well as a parasite. Its seeds germinate in the ground and the slender yellow green primary stem with rudimentary leaves rotates in anti-clockwise direction winding tightly around any stems it encounters. At frequent intervals haustoria penetrate the host. The stems of the Cassytha branch freely, but remain slender, festooning the shrub hosts with tangled stringlike masses. This species is restricted to the northern half of the Northland peninsula where it grows on shrubs and particularly manuka (Leptospermum scoparium). It is surprising to find that Cassytha belongs to the Lauraceae, a family otherwise of mostly tropical and subtropical trees including the species of Beilschmiedia and Litsea in New Zealand. Our species of Cassytha is also found in Australia and there are other species there and in Melanesia, tropical Asia and South Africa.
Vascular saprophytes are completely without chlorophyll and are often small, pale plants growing in leaf litter in very shady places in rain forests. It is thought that they gain their organic nutrients from decaying plant material. Their underground parts are penetrated by fungal threads and recent studies, some in New Zealand, have shown that in some cases the fungal threads are also attached to the roots of nearby trees. It is suggested that such saprophytes and probably others, may be secondary parasites drawing nutriment from tree roots via fungal threads.
The New Zealand saprophytes are all orchids, except for one belonging to the Burmanniaceae a family closely related to the Orchidaceae.
The one non-orchid is Thismia rodwayi. It has only been found in the northern half of the North Island and there mostly on the volcanic plateau. The pinkish scale-leaved stems, arising from a branching root system, each end in a relatively large delicate flower, which has been likened to a red lantern. Our species is also found in Tasmania and Victoria and there are other species in Australia, tropical Asia and America.
Corybas cryptanthus is the only saprophyte among the eight New Zealand species of the genus. It has been collected at scattered localities throughout the country. Only the flower appears above the leaf mold, the stem then elongating to carry the capsule to about 15 cm above the ground. The genus ranges from south-east Asia through Australia to New Zealand.
The 15 species of Gastrodia ranging from India and Japan to Australasia, are all saprophytes. The branching underground rhizomes are tuberous and filled with starch and those of our species were eaten by the Maoris. The stems are tall, up to one metre, and can be attractively if strangely coloured. They often appear as if polished, with flecks of white and brown giving a resemblance to wood grain.
C. cunninghamii, mostly in beech forest, and G. minor mostly under Leptospermum are found throughout. G. sesamoides has not been discovered further south than 42 degrees S in the South Island and is found in open forest and shrubland.
Yoania australis was only discovered in recent times, but is now known from several localities in Beilschmiedia tarairi forest on the Northland peninsula. The stems bearing the small flowers are a pale rose colour and up to 20 cm tall. The genus is entirely saprophytic and is known at several localities in Asia and north Africa.
In view of its wide range of specialised growth forms it is not difficult to conclude that New Zealand conifer broadleaf forest comes closer to tropical rain forest in this aspect than to any other type of vegetation despite New Zealand's temperate latitudes. In the light of certain fossil evidence the most likely explanation for this is that, before the Ice Age, forest of the general type now largely confined to tropical latitudes was also widespread in middle latitudes of both hemispheres. Plant fossils from the vicinity of London dating back to early Tertiary times (80 million years ago) belong to genera, including some of palms, now largely restricted to the tropics. Fossil floras with similar relationships have also been discovered in Oregon, U.S.A. The Ice Age, whose effects would have been more severe in the largely continental northern hemisphere, virtually eliminated such forests from middle northern latitudes while limited examples persisted in middle southern latitudes and in New Zealand best of all.
Remnants of such middle latitude rain forests, with fewer species than those of New Zealand and in particular fewer vines and epiphytes, can be found in parts of New South Wales and Victoria in Australia, along a portion of the south-east coast of South Africa and in Central Chile. The rain forests of these areas may have been more reduced than those of New Zealand by the development of arid continental climates and by their longer history of human and natural fires as well as by Ice Age coldness. New Zealand's narrow oceanic land mass would have ameliorated the two climatic factors and enabled the survival of our fascinating array of vines, epiphytes, parasites and saprophytes.
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1 This article is modified from a chapter in a forthcoming book — “Forest Vines to Snow Tussocks. The Story of New Zealand Plants.”
2 By contrast the larger vines and epiphytes are uncommon in or absent from beech (Nothofagus) forests. The mistletoe parasites, however, are more conspicuous in beech than in conifer broadleaf forest.
3 This is an interesting phenomenon also to be found in the equally variable leaves of juvenile pokaka (Elaeocarpus hookerianus), juvenile Pittosporum obcordatumand and seedling lancewood (Pseudopanax crassifolius).