Aquatic Plants
Plants that grow in water are called hydrophytes or aquatic plants. There are three types of aquatic plants - underwater plants, fixed plants and floating plants.
Underwater plants
Some plants remain completely beneath the surface of water. They are also called submerged plants. They have adapted to breathe under water.
Hydrilla and tape grass (Vallisneria) are underwater plants. Their roots fix them to the bottom of the pond. They have thin, flexible stems and finely dissected leaves that offer little resistance to water currents. Hydrilla has tiny leaves, while tape grass has narrow, ribbon-like leaves which bend in the flowing water.
They breathe through small air spaces present in their stem. The leaves of underwater plants do not have stomata. These plants are adapted to absorb carbon dioxide and oxygen from the water.
Fixed plants
These plants have roots that are fixed to the mud at the bottom of the ponds. They have adapted so that they can float, get enough air and sunlight to make food and prevent damage by flowing water. Lotus and water lily are some examples of fixed aquatic plants.
● Fixed aquatic plants have long and hollow stems with large air spaces. This helps the plants to stay afloat. Their soft and flexible stems bend with the flow of water. This prevents them from getting damaged by strong water currents.
● Their flat and broad leaves help these plants to get sufficient air and sunlight.
● The waxy coating on their leaves prevents them from rotting.
● Unlike most green plants, fixed aquatic plants have stomata present on the upper surface of the leaves. Such adaptive feature helps these plants to perform gaseous exchange from their surroundings.
Floating plants
These plants float freely in water. These plants can float with the flow of water as they do not have roots.
Water hyacinth and water lettuce (Pistia) are some examples of floating plants.
Floating plants have spongy bodies that are filled with air. This makes them light and helps them to float on water. Duckweed (Wolffia) is another example of a floating plant. Their floating leaves have chlorophyll only on the top of the surface.
