Evolution of Australasian Plantago (Plantaginaceae)
Phylogenetic analyses using molecular data were used to investigate biogeographic and evolutionary patterns of Australasian Plantago. The Internal Transcribed Spacers (ITS) from nuclear DNA, ndhF-rpl32 from chloroplast DNA and cox1 from mitochondrial DNA were selected from a primer assay of 24 primer pairs for further phylogenetic analyses. Phylogenetic reconstruction and molecular dating of a dataset concatenated from these regions comprising 20 Australasian Plantago species rejected a hypothesis of Gondwanan vicariance for the Australasian group. The phylogeny revealed three independent dispersal events from Australia to New Zealand that match expected direction because of West Wind Drift and ocean currents. Following this study, a dataset with 150 new ITS sequences from Australasian Plantago, combined with 89 Plantago sequences from previous studies, revealed that the New Zealand species appear to have a recent origin from Australia, not long after the formation of suitable habitats formed by the uplift of the Southern Alps (about 5 mya), followed by radiation. The ITS phylogeny also suggests that a single migration event of alpine species to lowland habitats has occurred and that recurrent polyploidy appears to be an important speciation mechanism in the genus. Species boundaries between New Zealand Plantago were unclear using both morphological and molecular data, which was a result of low genetic divergences and plastic morphology. The taxonomy of several New Zealand Plantago species need revision based on the ITS phylogeny.