Plant adaptation to O2-deficient waterlogged soils and flood-prone environments involves a suit of morphological, anatomical, and metabolic traits, as outlined in following sections. Plants need to cope with tissue anoxia, or avoid this adverse condition via a well-developed system of inter-connected gas-filled channels (aerenchyma) for internal O2 transport to supply submerged parts. Even species with large volumes of aerenchyma can experience anoxia in parts of their body, if only transiently. For these anoxic cells and tissues to survive, acclimative metabolic responses are essential. Furthermore, in addition to O2 deficits, plants must also cope with increased free radicals and reduced uptake of nutrients as additional components of flooding stress.