Arid Australia as a source of plant diversity: the origin and climatic evolution of Ptilotus (Amaranthaceae)

Abstract

In the present study, we tested the chronological and geographic origins of the mostly arid Australian Ptilotus (Amaranthaceae) and its close relatives (i.e. the ‘aervoids’) by reconstructing a dated phylogeny with near-comprehensive sampling for Ptilotus and estimating ancestral geographic ranges. We investigated climatic niche evolution within Ptilotus and identified likely climatic origins and subsequent niche shifts by reconstructing ancestral states of climatic variables on the phylogeny, which was visualised using a phyloecospace approach. Geospatial analyses were employed to identify probable diversification hotspots within Australia. We inferred that the aervoids originated in Oligocene Africa–Asia and that Ptilotus arrived in northern Australia by dispersal in the Early Miocene. Subsequent diversification of Ptilotus was rapid, giving rise to all major clades in the western Eremaean by the time of an aridification pulse in the Middle Miocene. Climatic niche shifts from the arid Eremaean into monsoonal northern and temperate southern Australia are apparent for multiple independent species groups. Our analyses support the hypothesis that a pre-adaptation to aridity and early arrival in an aridifying Australia were integral to the success of Ptilotus, and that the Eremaean has been a source of biodiversity in the genus and for independent radiations into neighbouring climatic zones.