New Zealand Journal of Botany abstracts

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Progress in understanding the natural history of New Zealand plants

DAVID G. LLOYD

Botany Department, University of Canterbury
Private Bag, Christchurch, New Zealand

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 biol- ogy. New Zealand plants, in general, have flowers that lack bright colours, are of small size, and have simple unspecialised structures. Dish and (espe- cially 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 adap- tations 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 polli- nators. The occurrence of conspicuous floral dis- plays 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 long- distance 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 differ- ential success of various groups on islands also constitutes species selection, caused by differential rates of persistence (versus extinction) and specia- tion. Plants with flowers that lack strong zygomor- phy appear to have speciated more extensively in New Zealand than plants with zygomorphic flow- ers. It is possible to estimate the relative impor- tance of individual selection and species selection in determining the distinctive features of island biotas. Species selection offers an explanation of the out- standing feature of the geography of extant New Zealand plants, the absence or low frequency of dominant Australian plant groups, such as Euca- lyptus (formerly present) and the Proteaceae, despite the occurrence of many species and genera in com- mon between Australia and New Zealand.

Keywords Rower structure; pollination mechanisms; dioecism; flower colour; divaricating habit; New Zealand biogeography; island biogeog- raphy; species selection; immigration selection

Received 27 February 1985; accepted 16 April 1985
New Zealand Journal of Botany, 1985, Vol. 23: 707-722
0028-825X/85/2304-0707$2.50/0 © Crown copyright 1985

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