Evolution of the New Zealand vascular flora: Regional and provincial patterns of richness, radiation, and endemism

Abstract

Analysis of species richness, radiation, and endemism in 171 list‐regions and 19 botanical provinces of the New Zealand botanical region indicates that the Late Cenozoic radiation of the New Zealand vascular flora has produced divergent phylogenetic trends in regional and provincial floras. Floristic richness at all taxonomic levels is strongly determined by land area. After accounting for area, most exceptionally species‐rich list‐regions occur immediately east of the South Island main divide, on calcareous substrates in West Nelson, or on several central North Island ranges. Depauperate floras are predominantly in the south on Auckland and Campbell Islands, and four Central Otago and two Southland ranges or basins. Family and genus richness decrease with latitude, but it appears that there has been compensatory radiation from a few herbaceous families in southern island and upland floras, so that species richness shows no latitudinal trend. We present a measure of aggregate regional endemism that is comparable between list‐regions and provinces of different floristic richness. Offshore island groups are the most insular floras, with exceptionally high endemism across different taxonomic ranks; northern island floras have high degrees of family and genus endemism and high phylogenetic diversity, while the subantarctic island floras have high species endemism and high radiation. In contrast, mainland botanical provinces all show average levels of regional endemism after correcting for species richness. With the exception of gymnosperms, the most New Zealand‐endemic plant groups have the most narrow regional distributions. We discuss latitudinal patterns of endemism among plant groups in terms of dispersal and adaptation. Land protection measures will achieve different phylogenetic outcomes in different landscapes across the New Zealand botanical region.

Keywords:

• New Zealand
• species richness
• bioge‐ography
• endemism
• radiation