Story: Shrubs and small trees of the forest
Page 4 – Species with juvenile and adult forms
From juvenile to adult
Some of the related subtropical trees and shrubs found in New Zealand forests have strikingly different juvenile and adult forms. This is called heteroblasty. As adult trees, they all have rounded crowns with simple or compound finger-like leaves, male and female flowers on separate trees, and flat clusters of dark berries. Most have less common close relatives with which they often form hybrids. Horticultural varieties are popular garden plants.
Horoeka – lancewood
Common throughout New Zealand, lancewood (Pseudopanax crassifolius) often forms patches in regenerating forest. Its easily recognised juvenile forms have tall, straight, unbranched stems up to 13 metres high. Long and narrow leathery mottled leaves hang from these stems like toothed umbrella ribs. This form persists for 15 to 20 years, until the growing tip begins to branch and the new leaves become shorter and less pendulous, forming a shaggy tuft. Eventually the tree develops simple oblong leaves and the rounded crown typical of this group. Adult lancewoods flower in late summer, and their purple berries ripen through the autumn.
P. ferox is a much less common type of lancewood, restricted to lowland forests in the two main islands. It has heavily toothed narrow juvenile leaves that are even more striking than those of P. crassifolius. The related shrubby P. linearis is found only on the western side of the Southern Alps.
Outsmarting the moa
Plants that change leaf and branch shape are common in New Zealand, though not elsewhere, as are those with a tangled (divaricating) form. It has been suggested that this was an adaptation to browsing by giant, flightless moa – dense, tangled plants would be difficult to eat. Once they have grown above the moa’s reach, they become larger-leaved adults. Another theory claims that such forms might have protected growing tips from wind, drought, and frost in ice ages. Alternatively, changing their form means that the plants can receive maximum light at different levels in the forest.
Haumakōroa (Raukaua simplex, formerly Pseudopanax simplex) is common from Thames southwards, in lowland to subalpine forests. Its shiny, deeply cut, three-lobed juvenile leaves change in adult trees to mostly simple leaves.
A close shrubby relative, R. anomalus, has the smallest leaves of this group, which also change from three-lobed in young plants to mostly simple in adults. But this species retains a divaricating growth form throughout its life.
Whauwhaupaku – five-finger
Five-finger (Pseudopanax arboreus) and the lookalike tree orihou (P. colensoi) do not have obvious juvenile forms.
Five-finger, one of the most common forest trees, is found in the lowland forests and scrub of both main islands, though it is rare in the western South Island. It has the round head characteristic of the group, compound leaves (with three to eight leaflets or fingers), and sweetly scented flowers that are produced in winter. Its flattened purple-black berries ripen during summer.
Orihou grows throughout New Zealand, from sea level to the subalpine shrub zone. It is smaller than five-finger, and its compound leaves, which have fewer fingers (three to five), are almost without stalks.
Patē – sevenfinger
Forming a shrub or small tree up to eight metres high, patē (Schefflera digitata) is the most tropical-looking of this group. It has large compound leaves, with as many as ten fingers, and large clusters of flowers. Patē is found only on moist sites, and along shady roadsides and stream banks. It produces long clusters of yellow-green flowers in late summer and early autumn, followed by bunches of black berries a few months later.
Different juvenile forms of patē are found only in the northern North Island, where young plants can have irregularly lobed leaves similar to those of haumakōroa.