Aquatic plants, also known as hydrophytes or hydrophytic plants, give life to a garden water feature. They provide hiding places and food for fish, as well as aerate the water and help prevent algae from overwhelming a pond. Aquatic plants are found in fresh and salt water nearly worldwide.
Flat leaves that float on the surface or beneath the water are characteristic of hydrophytes. The plants are not rigid because the water supports them. There is no need for branches or sturdy stems. There also is no need to monitor the intake or retention of water because water surrounds the plant. Many plants have air sacs to assist in floatation. Feather-like roots take in oxygen, resulting in less of a root system than land plants because hydrophytes get water directly into the leaves.
Problem Invasive Plants
Many natural water systems have become choked with aquatic plants that have overtaken the native species. The plants can be introduced in a number of ways. Home gardeners buying exotics for their onsite natural pond may not realize that the exotic can escape through streams and creeks that feed their pond and become invasive.
Many states have laws against the importation of invasive plants into their area. For example, Arizona prohibits the shipping of water hyacinth within state boundaries. The plants multiply vigorously in warmer waters.
Uses in Nature
Aquatic plants such as anacharis, which has dark feathery leaves, red Hygrophila with red flat sword-shaped leaves and money wort with bright green round leaves all add oxygen to the water and absorb impurities, helping keep the water clean and clear.
Food for fish is provided by floating plants such as salvinia with light green small leaves and azolla with tiny scale-shaped leaves. Fish love duckweed but it is considered an invasive plant in many areas. The tiny circular leaves can quickly take over the surface of the pond, and because the leaves are so tiny they are difficult to remove completely.
Many broad-leaf floating plants add a decorative touch to a pond but also provide shade from hot summer sun and a hiding place for fish from predators. Floating plants include New Zealand water snowflakes with purple edging around the leaves and small white flowers held above the water by their stems, and water lettuce, which looks like a loose head of lettuce.
Plants with long trailing root systems are good hiding places for fish fry and provide filaments for fish eggs to be attached so they can hatch.
Edible by Humans
Historically, many aquatic plants are edible and digestible by humans. These include cattails, arrowheads, watercress and water lily roots. Water chestnuts are featured in Chinese cooking. Taro roots form the basis of the Hawaiian dish of poi, a staple in that culture. Lotus tubers are stir fried.
A study titled "Accumulation of Lead, Cadmium, Zinc, and Copper in the Edible Aquatic Plants Trapa bispinosa Roxb. and Nelumbo nucifera Gaertn" conducted by M. Kumar, S. Chikara, M.K. Chand and A. K.Bhatnagar from the Environmental Biology Laboratory, Department of Botany, University of Delhi (http://www.springerlink.com/content/qbr6960kbh27ewja/) reported that aquatic plants can absorb heavy metals and those metals, at a high enough level, can be toxic. The quality of the water should be taken into consideration before eating any wild aquatic plants.