Historically rare plant species with disjunct population distributions and small population sizes might be expected to show significant genetic structure and low levels of genetic diversity because of the effects of inbreeding and genetic drift. Across the globe, terrestrial inselbergs are habitat for rich, often rare and endemic flora and are valuable systems for investigating evolutionary processes that shape patterns of genetic structure and levels of genetic diversity at the landscape scale. We assessed genetic structure and levels of genetic diversity across the range of the historically rare inselberg endemic Acacia woodmaniorum. Phylogeographic and genetic structure indicates that connectivity is not sufficient to produce a panmictic population across the limited geographic range of the species. However, historical levels of gene flow are sufficient to maintain a high degree of adaptive connectivity across the landscape. Genetic diversity indicates gene flow is sufficient to largely counteract any negative genetic effects of inbreeding and random genetic drift in even the most disjunct or smallest populations. Phylogeographic and genetic structure, a signal of isolation by distance and a lack of evidence of recent genetic bottlenecks suggest long-term stability of contemporary population distributions and population sizes. There is some evidence that genetic connectivity among disjunct outcrops may be facilitated by the occasional long distance dispersal of Acacia polyads carried by insect pollinators moved by prevailing winds. Keywords: gene flow; inselberg; isolation; landscape; phylogeographic structure INTRODUCTION For plant species, demographic and genetic connectivity is affected by seed and pollen dispersal vectors, by a number of life history traits including life form, longevity and the mating system, and by the size and spatial arrangement of populations. Rare plant species and those with specific habitat requirements often have geographically disjunct and small population sizes. For these species, the surrounding landscape typically comprises a matrix of unsuitable habitat that acts as an effective physical barrier to dispersal and the size and spatial arrangement of populations assumes an important role in the structuring and maintenance of genetic diversity. Limitations to connectivity result in a degree of demographic isolation and genetic isolation among populations (Slatkin, 1987), and produce the phylogeographic and genetic structuring observed in many habitat specific, rare, endemics (Yates et al., 2007;Byrne and Hopper, 2008;Butcher et al., 2009). Limited connectivity among disjunct populations can result in reduced levels of genetic diversity as a result of increased levels of inbreeding and via the negative impacts of genetic drift (Slatkin, 1987;Ellstrand, 1992), both of which are further enhanced in small populations. Structuring and maintenance of genetic diversity has a key role in the ultimate persistence of species as they evolve and adapt to changing conditions. As a result of ...