Plant terrestrialization (i.e. the transition to a terrestrial environment) is a significant evolutionary event that has been intensively studied. While certain plant lineages, particularly in angiosperms, have re-adapted to freshwater habitats after colonizing terrene, however, the molecular mechanism of the terrestrial-freshwater (T-F) transition remains limited. Here, the basal monocot Araceae was selected as the study object to explore the T-F transition adaptation mechanism by comparative genomic analysis. Our findings revealed that the substitution rates significantly increased in the lineage of freshwater Araceae, which may promote their adaptation to the freshwater habitat. Additionally, 20 gene sets across all four freshwater species displayed signs of positive selection contributing to tissue development and defense responses in freshwater plants. Comparative synteny analysis showed that genes specific to submerged plants were enriched in cellular respiration and photosynthesis. In contrast, floating plants were involved in regulating gene expression, suggesting that gene and genome duplications may provide the original material for plants to adapt to the freshwater environment. Our study provides valuable insights into the genomic aspects of the transition from terrestrial to aquatic environments in Araceae, laying the groundwork for future research in the angiosperm.