Mosquito fern in the context of "Aquatic plants"

Aquatic plants, also referred to as hydrophytes, are vascular plants and non-vascular plants that have adapted to live in aquatic environments (saltwater or freshwater). In lakes, rivers and wetlands, aquatic vegetations provide cover for aquatic animals such as fish, amphibians and aquatic insects, create substrate for benthic invertebrates, produce oxygen via photosynthesis, and serve as food for some herbivorous wildlife. Familiar examples of aquatic plants include waterlily, lotus, duckweeds, mosquito fern, floating heart, water milfoils, mare's tail, water lettuce, water hyacinth, and algae.

Aquatic plants require special adaptations for prolonged inundation in water, and for floating at the water surface. The most common adaptation is the presence of lightweight internal packing cells, aerenchyma, but floating leaves and finely dissected leaves are also common. Aquatic plants only thrive in water or in soil that is frequently saturated, and are therefore a common component of swamps and marshlands.

Neuston, also called pleuston, are organisms that live at the surface of a body of water, such as an ocean, estuary, lake, river, wetland or pond. Neuston can live on top of the water surface or submersed just below the water surface. In addition, microorganisms can exist in the surface microlayer that forms between the top- and the under-side of the water surface. Neuston has been defined as "organisms living at the air/water interface of freshwater, estuarine, and marine habitats or referring to the biota on or directly below the water's surface layer."

Neustons can be informally separated into two groups: the phytoneuston, which are autotrophs floating at the water surface including cyanobacteria, filamentous algae and free-floating aquatic plant (e.g. mosquito fern, duckweed and water lettuce); and the zooneuston, which are floating heterotrophs such as protists (e.g. ciliates) and metazoans (aquatic animals).The word "neuston" comes from Greek neustos, meaning "swimming", and the noun suffix -on (as in "plankton"). This term first appears in the biological literature in 1917. The alternative term pleuston comes from the Greek plein, meaning "to sail or float". The first known use of this word was in 1909, before the first known use of neuston. In the past various authors have attempted distinctions between neuston and pleuston, but these distinctions have not been widely adopted. As of 2021, the two terms are usually used somewhat interchangeably, and neuston is used more often than pleuston.