There are many plants that grow in or out of the water.
First group are those which will not grow in water, but are sold as aquarium plants by dealers. These will rot over a period of time. They can be decorative, but buyers should be told the truth.
Second group, true aquatic plants. These use the water for support, will flop into a heap out of water, will not grow out of water. Do not have "stiff" stems.
Third group are plants like Swords and Crypts. Most of these grow in areas where the water level changes drastically. They have one growth regime for emerged, a different for underwater. Often these plants have very different leaves when grown out of or underwater. They will grow in a tank without pause.
Fourth group, aqautic plants that live in the varying water level regime, but do not have emergent forms. They die down and rest during the dry period and sprout again when the rains return. Many of these plants grow at a phenominal rate when first planted, but do not survive underwater over a season, they require a drier, cooler "rest" period, examples are most Aponogeton species. Sadly, this group includes many of the most beautiful aquarium plants, but they are not popular because the buyer is not told how to care for them, hence they tend to drown.
