Plant adaptation to submergence can include the formation of prominent aerenchyma to facilitate gas exchange. Bartoli et al. investigate the ontogenesis of cortical aerenchyma in the stem of the aquatic macrophyte Egeria densa and find that formation of air spaces follows a well-orchestrated developmental program, consisting of a combination of an early schizogenous differentiation mechanism and a late lysigenous process that involves programmed cell death (PCD). The PCD remodels the architecture of the gas spaces previously formed schizogenously, and also results in a reduction of oxygen-consuming cells and in recycling of material derived from the lysigenic dismantling of the cells. The stems of E. densa thus enhance their metabolic efficiency and achieve optimal adaptation to submerged habitats.