1. Hundreds of Proteaceae species in Australia and South Africa typically grow on phosphorus (P)-impoverished soils, exhibiting a carboxylate-releasing P-mobilising strategy. In the Southwest Australian Biodiversity Hotspot, two Xylomelum (Proteaceae) species are widely distributed, but restricted within that distribution.

2. We grew X. occidentale in hydroponics at 1 μM P. Leaves, seeds, rhizosheath and bulk soil were collected in natural habitats.

3. Xylomelum occidentale did not produce functional cluster roots and occupied soils that are somewhat less P-impoverished than those in typical Proteaceae habitats in the region. Based on measurements of foliar manganese concentrations (a proxy for rhizosphere carboxylate concentrations) and P fractions in bulk and rhizosheath soil, we conclude that X. occidentale accesses organic P, without releasing carboxylates. Solution ³¹P-NMR revealed which organic P forms X. occidentale accessed.

4. Xylomelum occidentale uses a strategy that differs fundamentally from that typical in Proteaceae, accessing soil organic P without carboxylates. We surmise that this novel strategy is likely expressed also in co-occurring non-Proteaceae that lack a carboxylate-exuding strategy, and plants in similar habitats. These co-occurring species are unlikely to benefit from mycorrhizal associations, because plant-available soil P concentrations are too low.

5. Synthesis. Our findings show the first field evidence of effectively utilising soil organic P by X. occidentale without carboxylate exudation and explain their relatively restricted distribution in an old P-impoverished landscape, contributing to a better understanding of how diverse P-acquisition strategies coexist in a megadiverse ecosystem.

Soil chemical data. Soils were field-collected from natural habitats of Xylomelum occidentale. Soil data in this file include: pH, EC, total phosphorus (P), organic P, inorganic P. resin P, total carbon, soil organic matter, and soil organic carbon. This soil_chemical_data.csv file was created using Microsoft Excel 2013.

Leaf chemistry data: elemental concentrations. Leaves were field-collected from natural habitats of Xylomelum species. This leaf_chemistry_data.csv file was created using Microsoft Excel 2013.