Heteroblasty, or the character of having two or more distinct kinds of shoots, especially where the juvenile differ from the adult, occurs in many New Zealand plants. It is in fact one of the features of the vegetation and is not confined to any particular genus or family but is widespread. No plant possesses it more markedly than lancewood. This small tree grows in lowland and montane forest and shrubland throughout the three islands. The juvenile form is a characteristic of shrubland on the edge of forest.
In its adult form it is a small, round-headed tree, sometimes reaching a height of 40 ft. The trunk, which seldom exceeds 1 ft in diameter, is quite naked below the crown. Leaves are about linear or linear-oblong, 3–8 in. long, and are usually distantly toothed. There is a long-persisting juvenile form with a slender, unbranched main stem which gives off long, linear, deflexed rigid leaves which have large, sharp teeth. These leaves can be up to 3 ft long. Male and female flowers are on separate plants. They are very small and are in compound umbels.
There are two somewhat closely related species. P. ferox, a rather rare and local tree occurring from about latitude 35° southwards, has the same juvenile form as that of lancewood, except that the teeth are larger and hooked. The adult leaves are scarcely toothed. P. lineare is a shrub of high altitude forest or scrub. Leaves of juvenile plants ascend and the margins are wavy rather than toothed.
by Alec Lindsay Poole, M.SC., B.FOR.SC., F.R.S.N.Z., Director-General of Forests, Wellington.