Abstract

We examined the geographic origins and taxonomic placements of New Zealand and Australian Plantago (Plantaginaceae) by using molecular phylogenetic data. Plantago comprises over 200 species distributed worldwide. Analyses of three markers from the nuclear (ITS), chloroplast (ndhF–rpl32) and mitochondrial (coxI) genomes showed that the New Zealand species form three distinct, well supported clades that are not each others' closest relatives, and were each derived relative to the sampled Australian species. Therefore, at least three long-distance directional dispersal events into New Zealand can be inferred for Plantago, likely from Australian ancestors. This result differs from the biogeographic pattern often reported for New Zealand plant genera of a single dispersal event followed by rapid radiation, and may be attributed to ready biotic dispersal of mucilaginous seeds and habitat similarities of the Australasian species. Molecular dating placed the arrival time and diversification of the New Zealand species between 2.291 and 0.5 million years ago, which coincides with the geological dates for the uplift of mountain ranges in New Zealand. The mitochondrial DNA substitution rate of the Australasian clade relative to the rest of the genus is discussed, as well as implications of the non-monophyly of sections Oliganthos, Mesembrynia and Plantago within subgenus Plantago.