What type of plant grows entirely beneath the water surface?

Submergent plants are specifically adapted to grow entirely beneath the water surface. These plants are fully submerged in aquatic environments, such as ponds and lakes, and they play a crucial role in the ecosystem by providing habitat for aquatic organisms, improving water quality, and stabilizing sediment.

Unlike floating plants, which remain on the water's surface, and emergent plants that grow partially above water while their roots are submerged, submergent plants are fully underwater. Ferns, while they do exist in aquatic environments, are not exclusively aquatic and typically grow in moist soil rather than being entirely submerged. Thus, submergent plants accurately represent those consistent with the stated conditions of growing entirely below the water's surface.