We have recently obtained chromosome-level genome assemblies from representative species of three independently evolved seagrass lineages: Posidonia oceanica, Cymodocea nodosa, Thalassia testudinum, and Zostera marina. Comparative analysis of selected gene families suggests that the transition from submerged-freshwater to submerged-marine environments mainly involved fine-tuning of multiple processes (such as osmoregulation, salinity, light capture, carbon acquisition and temperature) that all had to happen in parallel, probably explaining why adaptation to a marine lifestyle has been exceedingly rare. Major gene losses related to stomata, volatiles, defence and lignification are probably a consequence of the return to the sea rather than the cause of it. All seagrass species also share an ancient whole-genome triplication, while additional whole-genome duplications were uncovered for C. nodosa, Z. marina and P. acutifolius. Polyploidy, or whole-genome duplication (WGD), serves as both a significant evolutionary force and a potential evolutionary dead end, particularly among angiosperms. Despite the prevalence of polyploid organisms, instances of ancient polyploidy are surprisingly rare, presenting a paradox that remains poorly understood. We recently also constructed a comprehensive genomic dataset of 470 angiosperm species and dated 132 ancient WGD events that are non-randomly distributed, revealing a clustering around pivotal periods of environmental upheaval and extinction. Notably, our findings highlight a strong correlation between waves of paleopolyploidization and significant events such as the Middle Miocene Disruption, the Eocene-Oligocene Transition (EOT), the Paleocene-Eocene Thermal Maximum (PETM), the Cretaceous-Paleogene (K-Pg) extinction, and different oceanic anoxic events (OAEs). We propose that polyploid organisms have an increased chance of survival during times of great environmental turmoil, a conclusion with important implications in the context of contemporary climate change and rapid global warming.