A dozen new spinifex species for the Pilbara have been described since 2015. With at least 26 species (and more likely), more than a quarter of Australia’s known species, the Pilbara is a centre of spinifex diversity. With 10 endemic and 5 near-endemic species, the Pilbara is also a centre of spinifex endemism. Eight species are of conservation concern, listed by the Western Australian Government as priority 1 or priority 3 species.
Spinifexes are ‘foundational species’ – dominating about a fifth of the Australian continent, used by many reptiles, mammals and birds for food, nesting and refuge from predators, competitors and extreme temperatures, and ecologically influential for their flammability.
The spinifex ancestors probably arrived in Australia from 14 to 24 million years ago (from where is not yet known) and diversified as Australia became more arid. But with so much of Australia offering suitable spinifex habitat, why does the Pilbara stand out for diversity and endemism?
A recent study of one spinifex group (the Triodia basedowii complex) suggests it is likely to have been a combination of increased speciation due to the diversity of the Pilbara landscape and reduced extinction due to refugia in the Pilbara. This group of spinifexes (previously known just as 2 species) is richest in the Pilbara, with 5 of 7 likely species occurring there, and 4 restricted or almost restricted to the region. They occur on different geologies in the Pilbara, suggesting that habitat specialisation has driven diversification. But with so few species elsewhere, it is also likely that refugia in the Pilbara have allowed spinifex species to persist that went extinct elsewhere during peaks of aridity.