Until 5 million years ago New Zealand had no snow-covered mountains. Most alpine plants and animals are thought to have evolved from lowland species as the mountains rose.
Mountain plants must withstand harsh freezing and thawing, drought, fierce ice-laden gales, and high levels of ultraviolet radiation. Many cling to exposed rock faces, steep slopes, shingle slides and screes and wrest nutrients from very poor soil and rocks.
Red, silver and snow tussocks predominate in the New Zealand alpine zone, with patches of stunted, wind-shorn shrubs, sprawling heath-like plants, grass trees and dense thickets of leatherwood.
Because alpine rocks, soil and water contain little nitrogen, two kinds of mountain plants get their nitrates by eating insects. These are the sundews, which catch insects on their sticky leaves, and the bladderwort, whose roots capture insects under water.
Alpine meadows, bogs, swamps and tarns are home to a great variety of attractive mountain flowers including gentians, eyebright, edelweiss, giant buttercups, and daisies. Many shrubs have brightly coloured berries to attract the birds and lizards that disperse their seeds.
Some plants resist the fierce drying winds by growing hairy, thick, woolly or fleshy leaves. Others hold on to their old leaves to insulate the plant against the wind and help retain water. The most curious of these is the huge, cushion-shaped vegetable sheep (Raoulia eximia). Other alpine plants form mats, or become succulents and grow long taproots to survive on ever-sliding screes or shingle slips.
New Zealand rivers and lakes once supported a wide range of native waterweeds, most of which have been supplanted by foreign species such as Canadian pond weed, oxygen weed and watercress. However, bogs, swamps and the banks of rivers and lakes are often still clothed with native species such as sedges, rushes, raupō, flax, cabbage trees, toetoe, and sphagnum moss.
Raupō (bulrush) is one of New Zealand’s few deciduous plants.
To withstand parching, salt-laden winds many coastal trees such as pōhutukawa, karaka, ngaio, nīkau palms and kohekohe, have developed thick or glossy leaves. Other species, such as the native ice plants and glasswort, hold water within their leaves and can tolerate higher salt levels than many other plants.
Tough grasses such as pīngao (Desmoschoenus spiralis) and spinifex (Spinifex sericeus) used to bind New Zealand sand dunes, but they have been largely taken over by foreign marram grass (Ammophila arenaria). Mangroves (Avicennia marina) thrive in the sluggish tidal mudflats north of Tauranga.