Aquatic plant

Aquatic plants, often called hydrophytes, are specialized vascular and non-vascular plants. They have adapted to live in aquatic environments, including both freshwater and saltwater. These plants are essential components of ecosystems like lakes, rivers, and wetlands. They provide vital cover for fish, amphibians, and aquatic insects. They also create a substrate for benthic invertebrates to live on. Through photosynthesis, they produce oxygen for the water. They also serve as food for various herbivorous wildlife.

To survive in water, these plants use unique biological mechanisms. A common adaptation is the presence of aerenchyma. These are lightweight internal packing cells that act like air pockets. This helps plants stay buoyant or float at the surface. Some plants also have finely dissected leaves. This shape helps reduce drag in moving river water. It also increases the surface area for exchanging minerals and gases. Some species, like Ranunculus aquatilis, even use two different leaf forms. They have dissected leaves underwater and entire leaves on the surface.

Floating-leaved plants have specific ways of breathing. Their leaves often have stomata, which are tiny pores, only on the top surface. This allows them to take in atmospheric carbon dioxide. Because they live in water, they do not risk dehydration through these pores. In fact, their stomata often remain in a permanently open state. Some aquatic angiosperms can also use bicarbonate from the water for carbon fixation. This is a trait not found in terrestrial plants. This allows them to thrive even in environments with low carbon levels.

Scientists classify these plants based on their morphology, or physical form. Large plants visible to the naked eye are called aquatic macrophytes. These are divided into several distinct growth types. Emergent plants grow in water but pierce the surface to reach the air. This allows them to be pollinated by wind or insects. Submerged macrophytes grow entirely underwater. Some are rooted to the bottom, while others are unrooted and free-floating. Floating-leaved plants have roots in the substrate but leaves on the surface. Finally, free-floating plants like water lettuce drift on the surface without being attached to the bottom.

Smaller aquatic plants are known as microphytes. These are microscopic and cannot be seen with the naked eye. They include phytoplankton, which are microscopic algae that drift with currents. They also include periphyton, which grow on the surfaces of rooted plants. Benthic algae live on submerged surfaces like mud or stones. Some are single-celled, such as diatoms, while others are multi-celled, like Spirogyra. These tiny organisms play a massive role in the aquatic food web.

History shows that aquatic plants have a deep evolutionary past. Aquatic vascular plants have originated on many different occasions. There are at least 50 independent origins within the angiosperms. This means different plant families evolved to live in water separately. One of the oldest known fossils is Archaefructus. This fossil is approximately 125 million years old. Evidence suggests that some of the earliest angiosperms were actually aquatic. While they are diverse, aquatic plants make up less than 2% of all angiosperm species.

Nature provides extreme examples of these adaptations. The Bolivian waterlily holds a Guinness World Record. It has the largest undivided leaf in the world. In contrast, the rootless duckweed is among the smallest. Some plants even change their position in the water column. The water soldier rests on the bottom as a rosette. In late spring, it slowly floats to the surface to flower. During this journey, it produces roots and daughter plants via rhizomes. Once flowering ends, the plant descends and its roots atrophy. This complex life cycle shows the incredible versatility of life in water.