New Zealand's pteridophyte flora—Plants of ancient lineage but recent arrival?

Abstract

A hypothesis is presented that most pteridophytes arrived in New Zealand relatively recently, by long-distance dispersal. The flora comprises 194 native species, of which 89 (46%) are endemic and 105 (54%) are widespread. Of the latter, 90% are shared with temperate Australasia, 53% with tropical regions, 14% with temperate southern Africa and 13% with the circum-Antarctic islands and South America. New Zealand has undergone such dramatic changes in location, land area, and topography since initial separation from Gondwana 85 Ma that it seems improbable that the 95 species shared with temperate Australasia could have remained conspecific throughout that time. Modern fossil and molecular evidence strongly suggest that many families of ferns had not even evolved prior to separation, and palynological evidence from New Zealand indicates that 78% of pteridophyte genera first appeared there only after separation from Gondwana. Present-day distributions in New Zealand suggest that ferns have greater dispersal potential than flowering plants, and that pteridophyte distributions are more heavily influenced by temperature, rainfall, and geothermal activity than by geological history. Most endemic pteridophyte species have a predominantly southern distribution pattern and are characteristic of cool, lowland to montane forest. Pteridophytes in the northern part of New Zealand show a lower level of endemism than elsewhere and tend to be widespread species that have arrived from temperate Australasian and tropical regions. There is also evidence that at least some pteridophytes have migrated from New Zealand to Australia. It is suggested that the hypothesis of long-distance dispersal of pteridophytes across the Tasman Sea could be tested by molecular techniques.