Forest Vines to Snow Tussocks: The Story of New Zealand Plants
The Hawaiian Islands lie in the tropical north Pacific. The islands in the group are mostly larger than Tahiti and the largest and southernmost, Hawaiʻi itself, has dome-like volcanoes, some still active, rising to over 4000 m. This is high enough to provide alpine conditions.
Hawaiʻi shares with New Zealand and Tahiti such genera as Metrosidews, Astelia and Coprosma, but has more species of them than Tahiti. It lacks Weinmannia, a genus important in some Tahitian and New Zealand forests. Species and varieties of Metrosideros dominate in most Hawaiian forests, particularly on the island of Hawaiʻi where some forms colonise lava flows and may form trees up to 30 m in height. In time other less light-demanding and shorter species enter the forests. They belong to such genera as Sapindus, Ilex, Osmanthus (some unite the Hawaiian species of this genus with Nestegis of New Zealand), Pittosporum, Myrsine and page 232Elaeocarpus. Tree ferns of the genus Cibotium may be common and sometimes bear a species of Cheirodendron (a genus related to Pseudopanax) as an epiphyte. There are also a few larger-leaved species of Coprosma, a long leaved Freycinetia and several species of Astelia both terrestrial and epiphytic. The Lobelia family has undergone remarkable development in Hawaiʻi with several genera and many species of shrubs and small trees, some of which are found in moist forests.
Apart from Metrosideros the only other large tree species is Acacia koa. This may be a component of Metrosideros forests or may dominate more open woodlands.
Above tree limit on the high volcanoes of Hawaiʻi and Maui there is low shrubby vegetation on well drained sites reminiscent of the mountain shrubland of the volcanic Mt. Ruapehu of New Zealand. Close inspection however reveals very few species including a Sophora, a small-leaved Styphelia, a Vaccinium with bright red, shiny berries, a few small-leaved Coprosmas, and a few ferns.
At higher levels still is a volcanic desert with few alpine species — a few grasses, small ferns, a few herbs in such genera as Fragaria and Geranium, and small shrubs such as the trailing small-leaved Coprosma ernodioides. The most remarkable alpine is the silversword (Argyroxiphium sandwicense) of the daisy family which is found only on Mt. Haleakela on Maui. It is somewhat like the Celmisias in New Zealand with sword-like leaves, but much larger, with the silvery-white leaves almost spherically arranged. The tall reddish flower heads are not unlike those of some of the Pleurophyllums of the New Zealand subantarctic.
Subalpine and alpine bogs have a much closer cover of plants. In less wet places there are dwarf shrubs of Metrosideros and other genera, but the wettest parts are essentially cushion bogs with cushions of Oreobolus, some grasses and species of Astelia. Scattered rosette herbs include Droseras (sundews) and species of Plantago, Geranium and Brachycome.