Abstract
Seagrasses feature a breathtaking range of adaptations for their successful return to the sea. Comparative genomics identified major re-arrangements related to light harvesting, hypoxic metabolism and salt tolerance across several seagrass lineages. Population-genomic approaches in the most widespread seagrass Zostera marina (eelgrass) uncovered multiple trans-Pacific dispersals from a species origin in the West Pacific, a recent entry into the Atlantic and a historical demography driven by glacial bottlenecks. Seagrass clones can diversify phenotypically through within-clone genetic and epigenetic evolution that may contribute to clonal adaptation and so explain their long persistence.