Aquatic plant - WikiHQ

thumb|The flower of [[Nymphaea alba, a species of water lily]]

thumb|Bud of [[Nelumbo nucifera, an aquatic plant]]

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, and water hyacinth.

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.

Evolution

Aquatic plants have adapted to live in either freshwater or saltwater. Aquatic vascular plants have originated on multiple occasions in different plant families; they can be ferns or angiosperms (including both monocots and dicots). The only angiosperms capable of growing completely submerged in seawater are the seagrasses. Examples are found in genera such as Thalassia and Zostera. An aquatic origin of angiosperms is supported by the evidence that several of the earliest known fossil angiosperms were aquatic. Aquatic plants are phylogenetically well dispersed across the angiosperms, with at least 50 independent origins, although they comprise less than 2% of the angiosperm species. Archaefructus represents one of the oldest, most complete angiosperm fossils which is around 125 million years old. These plants require special adaptations for living submerged in water or floating at the surface. When removed from the water, such plants are typically limp and lose turgor rapidly.

Those living in rivers do, however, need sufficient structural xylem to avoid being damaged by fast flowing water and they also need strong mechanisms of attachment to avoid being uprooted by river flow.

Many fully submerged plants have finely dissected leaves, probably to reduce drag in rivers and to provide a much increased surface area for interchange of minerals and gasses.

Some still-water plants can alter their position in the water column at different seasons. One notable example is water soldier, which rests as a rootless rosette on the bottom of the water body but slowly floats to the surface in late spring so that its inflorescence can emerge into the air. While it is ascending through the water column it produces roots and vegetative daughter plants by means of rhizomes. When flowering is complete, the plant descends through the water column and the roots atrophy.

In floating aquatic angiosperms, the leaves have evolved to only have stomata on the top surface to make use of atmospheric carbon dioxide. Gas exchange primarily occurs through the top surface of the leaf due to the position of the stomata, and the stomata are in a permanently open state. Due to their aquatic surroundings, the plants are not at risk of losing water through the stomata and therefore face no risk of dehydration. Angiosperms that use - can keep levels satisfactory, even in basic environments with low carbon levels. depending on whether they are large enough to be seen with the naked eye or are microscopic, respectively.

Emergent
Submerged
Rooted: rooted to the substrate
Unrooted: free-floating in the water column
Floating-leaved
Free-floating

Emergent

An emergent plant is one which grows in water but pierces the surface so that it is partially exposed to air. Collectively, such plants are emergent vegetation.
This habit may have developed because the leaves can photosynthesize more efficiently in air and competition from submerged plants but often, the main aerial feature is the flower and the related reproductive process. The emergent habit permits pollination by wind or by flying insects.
There are many species of emergent plants, among them, the reed (Phragmites), Cyperus papyrus, Typha species, flowering rush and wild rice species. Some species, such as purple loosestrife, may grow in water as emergent plants but they are capable of flourishing in fens or simply in damp ground.

Submergent

Submerged macrophytes completely grow under water with roots attached to the substrate (rooted submerged) (e.g. Myriophyllum spicatum) or without any root system (unrooted submerged) (e.g. Ceratophyllum demersum). They can also grow up to the water's surface. Helophytes are plants that grow partly submerged in marshes and regrow from buds below the water surface. Fringing stands of tall vegetation by water basins and rivers may include helophytes. Examples include stands of Equisetum fluviatile, Glyceria maxima, Hippuris vulgaris, Sagittaria, Carex, Schoenoplectus, Sparganium, Acorus, yellow flag (Iris pseudacorus), Typha and Phragmites australis. Instead, seaweeds have holdfasts that only serve as anchors and have no absorptive functions.

Floating-leaved

Floating-leaved macrophytes have root systems attached to the substrate or bottom of the body of water and with leaves that float on the water surface. Common floating leaved macrophytes are water lilies (family Nymphaeaceae), pondweeds (family Potamogetonaceae).

Free-floating

floating freely on the water's surface.
Free-floating macrophytes are found suspended on water surface with their root not attached to the substrate, sediment, or bottom of the water body. They may be easily blown by air and some may provide breeding ground for mosquitoes. Examples include Lemna spp or Pistia spp. the latter commonly called water lettuce, water cabbage or Nile cabbage.
Periphyton - a microphyte that lives and grows on the surface of rooted aquatic plants.
Benthic algae - relatively immobile algae that inhabit the submerged substrate surface of freshwater on mud, stones, or other relatively stable material. Algae may be single celled such as diatoms or Desmids, or multi-celled such as Spirogyra or Cladophora. A few such as some of the diatoms have limited abilities to move over their substrate.

Additional morphological classifications

The many possible classifications of aquatic plants are based upon morphology.

Amphiphytes: plants that are adapted to live either submerged or on land
Elodeids: stem plants that complete their entire lifecycle submerged, or with only their flowers above the waterline
Isoetids: rosette plants that complete their entire lifecycle submerged
Helophytes: plants rooted in the bottom, but with leaves above the waterline
Nymphaeids: plants rooted in the bottom, but with leaves floating on the water surface
Neuston: vascular plants that float freely in the water

Aquatic adaptations

Terrestrial plants in aquatic environments

Terrestrial plants may undergo physiological changes when submerged due to flooding. When submerged, new leaf growth has been found to have thinner leaves and thinner cell walls than the leaves on the plant that grew while above water, along with oxygen levels being higher in the portion of the plant grown underwater versus the sections that grew in their terrestrial environment. This is considered a form of phenotypic plasticity as the plant, once submerged, experiences changes in morphology better suited to their new aquatic environment. Because of this, their cell covering are far more flexible and soft, due to a lack of pressure that terrestrial plants experience. Terrestrial plants have rigid cell walls meant for withstanding harsh weather, as well as keeping the plant upright as the plant resists gravity. Gravitropism, along with phototropism and hydrotropism, are traits believed to have evolved during the transition from an aquatic to terrestrial habitat. Terrestrial plants no longer had unlimited access to water and had to evolve to search for nutrients in their new surroundings as well as develop cells with new sensory functions, such as statocytes.

Photosynthesis

Submerged aquatic plants have more restricted access to carbon as carbon dioxide compared to terrestrial plants. They may also experience reduced light levels. In water, light intensity rapidly decreases with depth. Respiration is also higher in the dark per the unit volume of the medium they live in. They compete with phytoplanktons for excess nutrients such as nitrogen and phosphorus, thus reducing the prevalence of eutrophication and harmful algal blooms, and have a significant effect on riparian soil chemistry as their leaves, stems and roots slow down the water flow, capture sediments and trap pollutants. Excess sediment will settle into the stream bed due to the reduced flow rates, and some aquatic plants also have symbiotic microbes capable of nitrogen fixation and breaking down the pollutants trapped and/or absorbed by the roots. and management of aquatic vegetation has become an increasingly interested field as means to reduce agricultural pollution of water bodies.

Functions of macrophytes in aquatic systems

Macrophytes perform many ecosystem functions in aquatic ecosystems and provide services to human society. One of the important functions performed by macrophyte is uptake of dissolved nutrients including nitrogen and phosphorus. Besides direct nutrient uptake, macrophytes indirectly influence nutrient cycling; especially N cycling through influencing the denitrifying bacterial functional groups that are inhabiting on roots and shoots of macrophytes. Macrophytes promote the sedimentation of suspended solids by reducing the current velocities, impede erosion by stabilising soil surfaces. Macrophytes also provide spatial heterogeneity in otherwise unstructured water column. Habitat complexity provided by macrophytes tends to increase diversity and density of both fish and invertebrates.The additional site-specific macrophytes' value provides wildlife habitat and makes treatment systems of wastewater aesthetically satisfactory.thumb|right|upright=1.25|World aquaculture production of food fish and aquatic plants, 1990–2016

Uses and importance to humans

Food crops

Some aquatic plants are used by humans as a food source. Examples include wild rice (Zizania), water caltrop (Trapa natans), Chinese water chestnut (Eleocharis dulcis), Indian lotus (Nelumbo nucifera), water spinach (Ipomoea aquatica), prickly waterlily (Euryale ferox), and watercress (Rorippa nasturtium-aquaticum).

Bioassessment

A decline in a macrophyte community may indicate water quality problems and changes in the ecological status of the water body. Such problems may be the result of excessive turbidity, herbicides, or salination. Conversely, overly high nutrient levels may create an overabundance of macrophytes, which may in turn interfere with lake processing.

Hot water extracts of the stem and root of Ludwigia adscendens, as well as those of the fruit, leaf and stem of Monochoria hastata were found to have lipoxygenase inhibitory activity. Hot water extract prepared from the leaf of Ludwigia adscendens exhibits alpha-glucosidase inhibitory activity more potent than that of acarbose.

Wastewater treatment

Macrophytes have an essential role in some forms of wastewater treatment, most commonly in small scale sewage treatment using constructed wetlands or in polishing lagoons for larger schemes. water movement, and salinity. and allelopathy are influencing the occurrence of macrophytes.

Invasive aquatic plants

The introduction of non-native aquatic plants has resulted in numerous examples across the world of such plants becoming invasive and frequently dominating the environments into which they have been introduced. Such species include water hyacinth which is invasive in many tropical and sub-tropical locations including much of the southern US, many Asian countries and Australia. New Zealand stonecrop is a highly invasive plant in temperate climates spreading from a marginal plant to encompassing the whole body of many ponds to the almost total exclusion of other plants and wildlifeOther notable invasive plant species include floating pennywort, curly leaved pondweed, Many of these invasive plants have been sold as oxygenating plants for aquaria or decorative plants for garden ponds and have then been disposed of into the environment.

Nutrient pollution and eutrophication

Excessive nutrient inputs, particularly nitrogen and phosphorus from agricultural runoff, sewage, and urban development, lead to eutrophication. This process results in algal blooms that reduce water clarity and oxygen levels, adversely affecting aquatic plants.In eutrophic conditions, submerged plant communities often decline, replaced by phytoplankton-dominated systems. This shift reduces habitat complexity and the availability of refuges for invertebrates and fish. Additionally, (micro)organisms decomposing algae consume oxygen, creating hypoxic "dead zones" where aquatic life cannot survive.

Climate-induced changes also affect water levels and flow regimes, impacting aquatic plant distribution and health. Droughts can reduce water availability, while intense storms can lead to increased runoff and sedimentation, both detrimental to aquatic vegetation.

Habitat degradation

Human activities such as urban development, agriculture, and dam construction lead to habitat degradation, posing significant threats to aquatic plants.

Urbanization increases impervious surfaces, leading to higher runoff volumes that carry pollutants and sediments into water bodies. This runoff can smother aquatic plants and alter water chemistry. Agricultural practices contribute to nutrient loading and pesticide contamination, further stressing aquatic vegetation.

Dam construction and water diversion projects alter natural flow regimes, affecting sediment transport and water temperature. These changes can disrupt the life cycles of aquatic plants and the species that depend on them.

Aquatic plants are integral to healthy aquatic ecosystems, but they face numerous threats from invasive species, nutrient pollution, climate change, and habitat degradation. Addressing these challenges requires integrated management approaches, including controlling invasive species, reducing nutrient inputs, mitigating climate change impacts, and protecting and restoring aquatic habitats.

Gallery

File:Nymphaea alba in Duisburg.jpg|Nymphaea - floating leaved

File:Water Lettuce (Pistia stratiotes).jpg|Pistia - free floating

File:Kleine Wasserlinse (Entengrütze).JPG|Lemna - free floating

File:Lotus flower (978659).jpg|Nelumbo - floating leaved

File:Azolla caroliniana kz04.jpg|Azolla - free floating

File:Salvinia natans (habitus) 2.jpg|Salvinia - free floating

File:Hydrocharis morsus-ranae kz11.jpg|Hydrocharis - free floating

File:Hydrocleys nymphoides 9675.jpg|Hydrocleys - floating leaved

File:Marsilea minuta 8915.jpg|Marsilea - floating leaved

File:Eichhornia crassipes 7839.jpg|Eichhornia - free floating

File:Juncus acutus 4.jpg|Juncus - emergent

File:Typha latifolia 02 bgiu.jpg|Typha - emergent

File:Myriophyllum aquaticum - side (aka).jpg|Myriophyllum - floating leaved

File:Hippuris vulgaris kz13.jpg|Hippuris - emergent and floating leaved

File:Stratiotes aloides LC0258.jpg|Stratiotes - floating leaved

File:Nymphoides ezannoi (aka).jpg|Nymphoides - free floating, submergent, and floating leaved

File:Eriocaulon, Paithalmala 6.jpg|Eriocaulon - emergent

File:Lobelia dortmanna kz06.jpg|Lobelia - emergent

</gallery>

References

External links

https://web.archive.org/web/20200410235322/https://aquaplant.tamu.edu/
Center For Aquatic And Invasive Plants
Aquatic Plant Monitoring in the State of Washington