Aquatic plant

Nymphaea alba, a species of water lily

Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or aquatic macrophytes. These plants require special adaptations for living submerged in water, or at the water's surface. Aquatic plants can only grow in water or in soil that is permanently saturated with water. Aquatic vascular plants can be ferns or angiosperms (from a variety of families, including monocots and dicots). Seaweeds are not vascular plants; rather they are multicellular marine algae, and therefore are not typically included among aquatic plants. As opposed to plant types such as mesophytes and xerophytes, hydrophytes do not have a problem retaining water, due to the abundance of water in their environment. This means that aquatic plants have less need to regulate transpiration, which would require more energy and be of little benefit to the plant.

Freshwater plants

Characteristics

Characteristics of aquatic plants:

• A thin cuticle. Thick cuticles reduce water loss; thus most hydrophytes have no need for thick cuticles.
• Stomata that are open most of the time, because water is abundant and there is no need for it to be retained in the plant. This means that guard cells on the stomata are generally inactive.
• An increased number of stomata, which can be on either side of the leaves.
• A less rigid structure: water pressure supports them.
• Flat leaves on surface plants for flotation.
• Air sacs for flotation.
• Smaller roots: water can travel directly into leaves through osmosis; thus large root systems are not required for water uptake.
• Feathery roots: no need to support the plant.
• Specialized roots able to take in oxygen.

For example, some species of buttercup (genus Ranunculus) float slightly submerged in water; only the flowers extend above the water. Their leaves and roots are long and thin and almost hair-like; this helps spread the mass of the plant over a wide area, making it more buoyant. Long roots and thin leaves also provide a greater surface area for uptake of mineral solutes and oxygen.

Wide flat leaves in water lilies (family Nymphaeaceae) help distribute weight over a large area, thus helping them float near surface.

Many fish keepers keep aquatic plants in their tanks to control phytoplankton and moss by removing metabolites.

Many species of aquatic plant are invasive species. Aquatic plants make particularly good weeds because they reproduce vegetatively from fragments.

Adaptations

Water lilies, with leaves floating on the water surface

• Floating plants: In an outdoor body of water, these receive more sunlight than submerged plants do. They also rarely have to compete with one another for sunlight
• Submerged plants: The leaves of submerged plants receive lower levels of sunlight because light energy diminishes while passing through a water column.

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All floating plants

• Either have air spaces trapped in their roots, or else air spaces in their bodies (aerenchyma) to help them to float, thus receiving adequate sunshine
• Have hair on their leaves that traps air
• Structural adaptations
• Have hollow stems to float on water.

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Duckweed, water cabbage

• Chloroplast found on the top surface of the leaves
• Upper Surface has a thick, waxy cuticle to repel water and to help keep the stomata open and clear
• Structural adaptation
• Small and light

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Water lily

• Structural material to reach higher points and receive more sunlight
• Structural adaptation

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Floating heart, water lily, lotus, yellow pond lily, water-shield

• Their leaves tend to be broader without major lobing, to remain flat on water surface, to enlarge their surface area, and to make use of as much sunlight as possible. Their chloroplasts are found on the tops of their leaves.
• Structural/ behavioral adaptations

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Most partially-submerged ("emersed") plants

• Air spaces within their tissues to keep them buoyant so that their leaves can reach the top of the body of water, in order to receive an adequate amount of sunlight
• Structural adaptation

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Dissected: Parrot's Feather, Hornwort
Thread-like: ditch-grass, quillwort

• Highly dissected/ divided leaves or thread-like ones, allows for a bigger surface area (surface to volume ratio)
• Structural adaptation

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Hydrilla

• Elongates rapidly to reach water surface and branches out at water surface; more light can be obtained at water surface
• Structural/ behavioral adaptation
• Xylem tubes are absent

Saltwater plants

Several aquatic plants live or are able to survive in brackish, saline, and salt water. Some are also grown commercially at or near shore. These include Salicornia, Aster tripolium, and Crambe maritima.

Human nutrition

Many aquatic plants are used by humans as a food source. Note that especially in (South-east) Asia edible but uncooked hydrophytes are implicated in the transmission of fasciolopsiasis. See also Fasciola hepatica.

• Wild rice (Zizania)
• Water caltrop (Trapa natans)
• Chinese water chestnut (Eleocharis dulcis)
• Indian Lotus (Nelumbo nucifera)
• Water spinach (Ipomoea aquatica)
• Watercress (Rorippa nasturtium-aquaticum)
• Water mimosa (Neptunia natans)
• Taro (Colocasia esculenta)
• Rice (Oryza) is originally not an aquatic plant.
• Bulrush, reedmace, or cattail (Typha)
• Water-pepper (Polygonum hydropiper)
• Wasabi (Wasabia japonica)
• Kjosco
• Totora (Scirpus californicus)

Animal nutrition

Some examples of aquatic plants

• Water hyacinth (Eichhornia)
• Duckweed: Lemna, Spirodela and Wolffia
• Trichanthera gigantea

Some examples of aquatic plants

• Most algae, and all seaweed and kelp
• Riella, the only genus of liverwort to grow as a submerged aquatic.
• Utricularia (from the Latin, utriculus, a little bag or bottle) is a genus of slender aquatic plants, the leaves of which contain floating air bladders. They are called bladderworts.
• Water lettuce

See also

• Aqua Planta
• Aquascaping
• Aquatic animal
• Aquatic Botany
• Bog
• Commercial production of aquatic plants
• Helophyte
• List of freshwater aquarium plant species
• Marsh
• Paddy field
• Salt marsh
• Sea grass
• Swamp gas
• Xerophyte

Source

• Cook, C.D.K. (ed). 1974. Water Plants of the World. Dr W Junk Publishers, The Hague. ISBN 90-6193-024-3

External links

• Aquatic Plant Finder
• PlantGeek.net