The flora of ultramafic soils in the Australia–Pacific Region: state of knowledge and research priorities

Abstract

In the Australia–Pacific Region ultramafic outcrops are both widespread and extensive, covering thousands of km2. Soils derived from ultramafic bedrock impose edaphic challenges and are widely known to host highly distinctive floras with high levels of endemism. In the Australia–Pacific Region, the ultramafics of the island of New Caledonia are famed for harbouring 2150 species of vascular plants of which 83% are endemic. Although the ultramafic outcrops in Western Australia are also extensive and harbour 1355 taxa, only 14 species are known to be endemic or have distributions centred on ultramafics. The ultramafic outcrops in New Zealand and Tasmania are small and relatively species-poor. The ultramafic outcrops in Queensland are much larger and host 553 species of which 18 (or possibly 21) species are endemic. Although New Caledonia has a high concentration of Ni hyperaccumulator species (65), only one species from Western Australia and two species from Queensland have so far been found. No Ni hyperaccumulator species are known from Tasmania and New Zealand. Habitat destruction due to forest clearing, uncontrolled fires and nickel mining in New Caledonia impacts on the plant species restricted to ultramafic soils there. In comparison with the nearby floras of New Guinea and South-east Asia, the flora of the Australia–Pacific Region is relatively well studied through the collection of a large number of herbarium specimens. However, there is a need for studies on the evolution of plant lineages on ultramafic soils especially regarding their distinctive morphological characteristics and in relation to hyperaccumulation.