Some aquatic plants, such as Nymphaea, have floating leaves while their root systems are anchored to the bottom of the lake or river and the shoot remains just above the substrate. The shoot apical meristem produces leaves with elongated petioles that allow the leaf blade to float on the surface of the water. The petiole contains aerenchyma, a spongy tissue with large air spaces found between the cells, that helps the leaf float. As water level rises and falls, the flexible petiole allows the blade to remain at the water's surface. The leaves are often peltate in shape. When leaves become crowded together some shading of neighboring leaves may occur. Victoria regina, the royal water lily, has huge peltate leaves with upturned leaf margins that prevent the leaves from overlapping.

      Completely submerged aquatic plants can only grow in water bodies that are shallow enough to permit light to penetrate to them. Many have rosette shoots and highly dissected leaf blades. Aponogeton fenestrale leaf blades have vascular tissue surrounded by a single layer of chlorenchyma. The spaces between the vasculature result from apoptosis (programmed cell death). The spaces allow highly turbulent water to pass through the leaf blade without shredding it.

      Free-floating aquatic plants are not rooted in a substrate but exist entirely on the water's surface. Some species have root-like structures that facilitate nutrient absorption and others have reduced root systems that act as a keel to keep the plant upright. Eichornia crassipes, the water hyacinth, has leaves with aerenchyma filled bulbous petioles that keep them afloat. Pistia has leaves covered with hairs that "trap" air bubbles to ensure the plant stays above water. Many free-floating aquatic species are extremely small. Wolffia and Spirodela are examples of these small aquatic plants that tend to form colonies on the water's surface.

      Free-floating ferns exhibit the same kinds of structural adaptations to an aquatic environment as the angiosperms mentioned above. Azolla filiculoides has a single root that acts like a keel. The leaves of Azolla are inhabited by a nitrogen-fixing bluegreen alga. These water ferns are grown on rice paddies and provide a source of nitrogen to the rice plants when the ferns die. Salvinia is a free-floating fern with three leaves per node: two trichome-covered leaves remain above water and one submerged highly dissected leave that looks like a root but bears sporangia.