Charles Darwin was unimpressed with the south coast of Western Australia when he visited in March 1836 calling it ‘dull and uninteresting’. If, however, he had visited during the spring wildflower season its likely he would have come to the opposite conclusion.
These days botanically-inclined tourists, such as myself, flock to southwestern Australia during wildflower season. The region is one of 35 global biodiversity hotspots recognized by Conservation International. Collectively these hotspots represent only 2.3% of the Earth’s surface but contain more than half of the living species.
The southwestern Australian hotspot is estimated to contain over 7000 plant species, with around half endemic (occurring nowhere else). For comparison New Zealand, another hotspot, has a mere 2500 native plant species. Western Australian botanists have certainly been busy recently with a third of the 7000 species being described since 1970.
So why is this particular region so diverse? Southwestern Australia is one of the oldest and geologically-stable landscapes on Earth with no mountain-building or glaciation occurring in the last 300 million years. This stability is thought to have selected for species that are able to persist locally, rather than disperse widely and colonise new areas.
Many species don’t have an obvious means of dispersing their seeds, e.g they lack fleshy fruits to entice birds and mammals to disperse seeds in their droppings. Instead, seeds tend to end up no more than a few metres from their maternal parent. Consequently many species have very restricted distributions and are now highly susceptible to human-induced disturbances, such as habitat loss and fragmentation, introduced weeds and root-rot disease (Phytophthora). In fact southwestern Australia now has more threatened species than most countries!
If you are visiting Western Australia but don’t have time to roam far then King’s Park and Botanic Gardens in Perth has over 3000 species of the state’s plants on display and is well worth a visit.