Where and why have all the flowers gone? Depletion and turnover in the NewZealand Cenozoic angiosperm flora in relation to palaeogeography and climate

The modern New Zealand angiosperm flora has many notable characteristics, s uch as a predominance of evergreen, perennial life forms, few nitrogen-fixi ng species, despecialised floral features and asymmetric genus-species rela tions. The origin of these features has been attributed to antiquity of the flora, isolation and/or environmental history. Using evidence from palynol ogy and macrofossils, we investigate the characteristics of the mid-late Ce nozoic angiosperm flora and the impact of environmental changes in land are a and configuration, physiography and climate on the depletion and composit ion of the New Zealand flora. Climatic cooling, increasing isolation and te ctonism have each acted as important environmental filters, contributing to regional extinctions and decreasing floral diversity, and inducing major t urnover in the floristic composition of New Zealand. During the Miocene and Pliocene at least 15 families and a minimum of 36 genera were lost from th e New Zealand flora. These included a range of life forms and physiognomica lly important taxa such as Acacia, Bombax, Casuarina, Eucalyptus, Ilex, man y Proteaceae and several palms. The extinction and decline in richness of s ubtropical families was caused by the onset of cooling conditions in the La te Miocene-Pliocene, and exacerbated by the absence of significant land are as to act as refugia at lower latitudes. Many of these genera/families pers ist today on islands to the north (e.g. New Caledonia), reflecting mid-Ceno zoic land conduits, and in Australia. The close floristic links with New Ca ledonia were probably maintained by intermittent island stepping-stones whi ch facilitated interchange of subtropical taxa until the Late Miocene. The Pleistocene extinction of some genera, tolerant of warm-temperate environme nts (e.g. Acacia, Eucalyptus) may be a reflection of the fact that persiste nt mesic conditions favoured widespread dominance of dense rainforest durin g interglacials. The loss of these groups, containing diverse life forms an d floral structures, suggests that many of the present characteristics of t he New Zealand flora reflect strong selective pressures, mainly driven by c limate change, in the Late Miocene, Pliocene and Pleistocene, rather than e vents of greater geological antiquity.