Progress in understanding the natural history of New Zealand plants

Abstract

In investigations of the reproductive biology of New Zealand plants, breeding systems have received much attention but there has been little work on pollination and still less on seed biology. New Zealand plants, in general, have flowers that lack bright colours, are of small size, and have simple unspecialised structures. Dish and (especially at higher altitudes) tube blossoms abound, whereas bell, brush, gullet, and flag blossoms are relatively uncommon. There is an unusually high frequency (c. 18 per cent) of genera with separate sexes. New Zealand has few specialised pollinators. The unspecialised flowers are interpreted as adaptations to fluctuating combinations of promiscuous pollinators. The high frequency of separate sexes is associated with unspecialised pollinators and fleshy bird-dispersed fruits. A number of larger genera show considerable evolution of flower structure accompanying respecialisation to different pollinators. The occurrence of conspicuous floral displays on certain outlying islands is a puzzling anomaly in view of the depauperate insect faunas on these islands.A simple methodology is presented for deciding whether the evolution of distinctive characters on isolated islands such as New Zealand has occurred on the islands or on the source areas before longdistance dispersal to the islands. The evolution of simple despecialised flowers in Melicytus and 18 out of 20 cases of divaricating habits are proposed as examples of the autochthonous evolution of New Zealand peculiarities. In contrast, c. 68 out of 80 cases of the aquisition of separate sexes in New Zealand plants are derived from immigration of dimorphic ancestors.Non-random dispersal to islands of plants with different characters is a form of species selection, described here as “immigration selection”, which is exemplified by the more frequent migration of bird-dispersed plants to New Zealand. The differential success of various groups on islands also constitutes species selection, caused by differential rales of persistence (versus extinction) and speciation. Plants with flowers that lack strong zygomorphy appear to have speciated more extensively in New Zealand than plants with zygomorphic flowers. It is possible to estimate the relative importance of individual selection and species selection in determining the distinctive features of island biotas.Species selection offers an explanation of the outstanding feature of the geography of extant New Zealand plants, the absence or low frequency of dominant Australian plant groups, such as Eucalyptus (formerly present) and the Proteaceae despite the occurrence of many species and genera in common between Australia and New Zealand. © 1985 Taylor & Francis Group, LLC.