Phylogenetic investigation and divergence dating of P oa ( P oaceae, tribe P oeae) in the A ustralasian region

The A ustralasian region contains a significant proportion of worldwide P oa diversity, but the evolutionary relationships of taxa from this region are incompletely understood. Most A ustralasian species have been placed in a monophyletic P oa subgenus, P oa supersection H omalopoa section B rizoides clade, but with limited resolution of relationships. In this study, phylogenetic relationships were reconstructed for A ustralasian P oa , using three plastid ( rbc L and mat K genes and the rpl32‐trn L intergenic spacer) and two nuclear [internal/external transcribed spacer ( ITS / ETS )] markers. Seventy‐five P oa spp. were represented (including 42 A ustralian, nine N ew G uinean, nine N ew Z ealand and three A ustralian/ N ew Z ealand species). Maximum parsimony, maximum likelihood and B ayesian inference criteria were applied for phylogenetic reconstruction. Divergence dates were estimated using B ayesian inference, with a relaxed clock applied and rates sampled from an uncorrelated log‐normal distribution. A ustralasian P oa spp. are placed in three lineages (section B rizoides , section P arodiochloa and the ‘ X clade’), each of which is closely related to non‐ A ustralasian taxa or clades. Section B rizoides subsection A ustralopoa is polyphyletic as currently circumscribed. In A ustralasia, P oa has diversified within the last 4.3 Mya, with divergence dating results broadly congruent with fossil data that record the appearance of vegetation with a prominent grassland understorey or shrubland/grassland mosaic vegetation dating from the mid‐Pliocene. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society , 2014, 175 , 523–552.