Localised abundance and semi-continuous distribution maintain connectivity and genetic diversity in Synostemon hamersleyensis, a rare ironstone-endemic in north-western Australia

Context Rare plant species in arid regions may be vulnerable to genetic erosion, potentially influenced by constrained dispersal mechanisms. Aims To assess spatial patterns and underlying drivers of genetic variation in Synostemon hamersleyensis, a narrow endemic species in the ironstone ranges of the Pilbara region, north-western Australia. Methods We used range-wide sampling across 27 sites and the generation of genome-wide single nucleotide polymorphism data to assess how patterns of genetic diversity and differentiation correlate with geographic, environmental and resistance factors. Key results Moderate levels of genetic diversity, alongside elevated inbreeding and weak genetic structure, suggest that near-neighbour mating is typical. Multivariate regression analyses identified resistance distance as the strongest predictor of genetic differentiation. Environmental distance had no significant effect, while geographic distance contributed modestly, indicating that spatial proximity plays a greater role than ecological variation in shaping genetic structure across the species’ narrow range. Connectivity was strongest in central areas, with smaller zones of exchange among peripheral sites. Conclusions Whilst restricted to a narrow range, high localised abundance and semi-continuous distribution facilitate stepping-stone gene flow to maintain and distribute genetic variation across the species’ range. Implications Conservation management should prioritise maintaining the integrity of the species’ habitat and distribution to preserve these natural dynamics and support long-term persistence under intensifying land-use pressures.