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Pondweed is the term used to describe a number of freshwater aquatic plants and green algae from the Potamogeton genus. These types of plants occur throughout the world, the Elodea variety being found in North America and the Aponogeton variety occurring in Asia, Australia and Africa; examples of these plants include the American, the Illinois, the Sago, the Southern naiad, the Curly-leafed and the Variable-leaf pondweed. These are perennial, fast-spreading plants, and, although used for decorative purposes in gardens and aquariums, they have become problematic as an invasive weed in some areas.
The Potamogeton plants arise from rhizome or tuber roots, and send out long, highly branched stems and quantities of floating and submerged leaves; some of the plant varieties do not have floating leaves. In shape, the floating leaves, depending on the plant type, may be oval, round, oblong, heart-shaped, curly, spiny or with serrated edges. The floating leaves are generally thick or leathery in texture and are broader than the submerged leaves. The submerged leaves, which are found in all pondweed varieties, are blade-or filament-like, and are usually thin and translucent. The floating and submerged leaves of different varieties may vary in color from yellowish to pale green to dark green to deep purple.
The plant's flowers appear above the water surface, produced either singly or in dense spikes. Some of the common floral colors are yellow, white, pink, red and purple. The flowers can range in size from large to tiny. The fruit may be round or flat, and may be produced in spikes of nutlets. New plants arise from seeds or from the spreading rhizomes.
The underwater roots, stems and leaves of the pondweed help keep it well-oxygenated. They also provide a haven for many microorganisms and invertebrates. These creatures, together with the plant tubers, floating leaves, flowers, and fruit, serve as an important food source for a number of higher animals. When the plants die, they are decomposed by the water bacteria and fungi and returned to the food cycle to be consumed by the microorganisms.
As these types of plants are very hardy, they can thrive even in cold, icy conditions and can quickly edge out other aquatic plants. It can be quite difficult to cull pondweed once it has become entrenched, especially if it has spread over a large water area. Some of the methods used to get rid of these plants include mechanical removal, dredging, using herbicides, using aquatic dye and adding pondweed-eating grass carp.