Global distribution of a land plant by means of oceanic dispersal

The geographic range of species is one of the key indicators of their evolutionary success. Unlike animals, most plants are immobile and expand their range primarily through long-distance dispersal (LDD) of seeds. Seeds can be dispersed over very long distances, especially by ocean currents. However, little is understood about the role of ocean currents in LDD and the contribution of land barriers to genetic differentiation on a global scale. To investigate the outermost limits of LDD by ocean currents in land plants, we studied Canavalia rosea (Sw.) DC. (Fabaceae), which is distributed throughout littoral areas of the tropics and subtropics around the world. Our results using DNA sequences from six chloroplast regions and two low-copy nuclear loci from 436 individuals in 37 populations revealed that ocean currents played a crucial role in the species range expansion and maintaining its global distribution despite the constraints by continental barriers. These suggest that the global distribution of C. rosea is the result of recent transoceanic dispersal within and between the Atlantic and Indo-Pacific oceans, while the Isthmus of Panama has prevented gene flow across the American continents. These results highlight the power of oceanic seed dispersal in shaping plant biogeography.