Alpine shrubs

Above the actual or inferred treeline come shrubs that can be considered truly alpine, although many descend to lower altitudes in open habitats. Immediately above treeline on moderate slopes with a reasonably well developed soil such shrubs generally intermingle with large tussock grasses and other herbs in what has been termed tussock-shrubland. As altitude increases, the shrubs decrease and the herbs increase. On steeper slopes, such as spurs and ridges, with shallow, stony soils, species of shrubs mostly different from those of the tussock-shrubland may form a more continuous cover, but there is usually a herb component. On these rocky sites certain shrubs may extend to quite high altitudes, becoming shorter and more scattered as they do so.

It is in this higher shrubland zone that New Zealand's largest genus Hebe attains its greatest prominence. Of the approximately 60 commoner species of alpine shrubs 24 or 40 per cent are hebes, many of them exhibiting the symmetry of form and attractiveness of foliage — grey-green, yellow-green and shades of yellow and orange — that have made the genus so well known horticulturally in many parts of the world. The alpine hebes can be divided into two approximately equal groups contrasting strongly in growth habit. In the first group the leaves, although short and fairly broad, are spreading and often very precisely arranged in four vertical rows. The shapes of such shrubs may be so symmetrical and their surfaces so dense, that they appear to have been trimmed to shape. Appropriately, one of them has been named Hebe topiaria. The relationship of the hebes in this group with the willow-leaved species (koromikos) of the lowlands is quite evident, but with the second group of so-called 'whipcord' hebes this is not so; they resemble instead the quite unrelated scale-leaved conifers (Fig. 93). It is no surprise to learn that one of them is named Hebe cupressoides. Both growth forms are represented in tussock-shrubland and on stony ridges.

Similar in general appearance to the hebes with spreading four-ranked leaves are a number of species of Pimelea or New Zealand 'daphnes'. The flowers with their pairs of stamens are also quite Hebe-like, but as a general rule the two genera can be distinguished by the presence (Pimelea) or absence (Hebe) of leaf and flower hairs. Pimelea leaves often feel quite silky to touch. Pimeleas occur both in grassland and on rocks.

Most of the alpine dracophyllums have needle leaves. Taller species in tussock-shrubland have a switch-like habit with narrow branching angles, others in similar habitats or on rocky ridges are more or less prostrate. During the colder period of the year especially, the dracophyllums add colour to the alpine scene when their leaves develop bright reddish brown hues.

A few gaultherias belonging to the Ericaceae or heath family also occur in alpine communities. Gaultheria crassa is a shrub up to 1 m high growing in a variety of sites. The clusters of small white flowers are bell-like and not unlike those of the dracophyllums. The leaves, however, are short, broad and quite thick. Gaultheria depressa var. novae-zelandiae is a prostrate shrub in open places remarkable for its relatively large white, pink or red, berry-like fruits often referred to as 'snow berries'. The page 169

Figure 93 (left) Hebe tetragona. A 'whipcord' Hebe.
Photo: M. D. King.

Figure 94 (right) Gaultheria depressa. The upper fruit has had part of the fleshy calyx removed to reveal the seed capsule.
Photo: M. D. King.

fleshy parts of the fruits are actually the persistent and enlarged sepals of the flowers (Fig. 94). Pernettya macrostigma, which belongs to a genus closely related to Gaultheria, is a scrambling, interlaced shrub of poorly drained areas in tussock grassland. It has an even more remarkable fruit than that of Gaultheria depressa, as both the persistent sepals and the seed capsule within them are fleshy. Natural hybrids between Pernettya macrostigma and a Gaultheria have bright red fruits in which the plump sepals form a crown-like cup around the capsule.

All except one of the relatively few shrubby alpine coprosmas have very small leaves and slender twigs. Three of these are prostrate and scrambling, C. cheesemanii and C. crenulata in damp places in tussock grassland and C. depressa on rocky sites. Coprosma pseudocuneata with its attractive, strongly recurved, yellowish green leaves has an erect habit and extends to quite high altitudes in sheltered rocky sites. The one large-leaved Coprosma, C. serrulata, grows in shaded tussock shrubland page 170 and also on shaded rocky bluffs. Its leaves are thick and leathery with prominent veins.

The Compositae or daisy family is represented by a few species belonging to three genera.

Brachyglottis (Senecio) bidwillii is widespread in tussock shrubland and on rocky bluffs. Its leaves are rounded and very thick with a thick, feltlike mass of hairs on their undersides. Two other species are more localised, B. adamsii in adjacent parts of the North and South Islands, and B. revolutus in the south-west of the South Island.

The genus Helichrysum, which includes the flowers known as 'everlastings', has several shrubby alpine species in the drier eastern mountains of the South Island where they grow on rocky outcrops and ridges. They all have a similar distinctive appearance with scale-like, but somewhat swollen, strongly convex leaves closely pressed to the stems. The rounded backs of the leaves may be very shiny and each leaf is surrounded by a dense mass of white hairs. The most robust and striking species is Helichrysum coralloides with cylindrical stems up to 1 cm in diameter.

Cassinia vauvilliersii may be common in tussock-shrubland throughout New Zealand as well as in open vegetation at lower altitudes. It is an erect shrub, often with a distinct yellowish colouration from the hairs on the undersides of the small leaves.

Melicytus (Hymenanthera) alpinus of the violet family is a small shrub with short, stiff, interlacing twigs which are almost spiny at the tips. The species occurs throughout the South Island and is most frequent on rocky ridges and outcrops.

Myrsine nummularia is a small-leaved, prostrate, thin-stemmed shrub found throughout the New Zealand mountains where it favours rock outcrops and open places in tussock grassland. Its most striking feature is the bright violet-blue colouration of the berries.

Three dwarf conifers may be frequent throughout tussock shrubland. Snow totara (Podocarpus nivalis) forms low bushes in this community, but is also common at scree margins and on moraines at lower elevations. The pigmy pine (Lepidothamnus laxifolius), sometimes called the smallest conifer in the world, forms even lower mat-like patches in poorly drained sites and the mountain celery pine (Phyllocladus aspleniifolius var. alpinus) is still erect in habit though shorter than it is in the subalpine shrublands.