Aquatic plants also referred to as hydrophytes [1] are vascular plants and non-vascular plants [2] 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. [3] Familiar examples of aquatic plants include waterlily, lotus, duckweeds, mosquito fern, floating heart, water milfoils, mare's tail, water lettuce, water hyacinth, and algae. [4]
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. [5] [6] [7] Aquatic plants only thrive in water or in soil that is frequently saturated, and are therefore a common component of swamps and marshlands. [8]
Aquatic plants have adapted to live in either freshwater or saltwater. Aquatic vascular plants have originated on multiple occasions in different plant families; [5] [9] they can be ferns or angiosperms (including both monocots and dicots). The only angiosperms capable of growing completely submerged in seawater are the seagrasses. [10] 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. [11] Archaefructus represents one of the oldest, most complete angiosperm fossils which is around 125 million years old. [12] These plants require special adaptations for living submerged in water or floating at the surface. [12]
Fully submerged aquatic plants have little need for stiff or woody tissue as they are able to maintain their position in the water using buoyancy typically from gas filled lacunaa or turgid Aerenchyma cells. [13] When removed from the water, such plants are typically limp and lose turgor rapidly. [14]
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. [13] Some species of plants such as Ranunculus aquatilis have two different leaf forms with finely dissected leaves that are fully submerged and entire leaves on the surface of the water.
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. [15] 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. [15] For carbon fixation, some aquatic angiosperms are able to uptake CO2 from bicarbonate in the water, a trait that does not exist in terrestrial plants. [16] Angiosperms that use HCO
3- can keep CO2 levels satisfactory, even in basic environments with low carbon levels. [16] The many possible classifications of aquatic plants are based upon morphology. [5]
Aquatic plants are either aquatic macrophytes or aquatic microphytes. [17] Aquatic macrophytes are hydrophytes that are large enough to be seen with the naked eye. [18] Aquatic microphytes are hydrophytes that cannot be seen with the naked eye; they are microscopic. [17]
Based on growth form, macrophytes can be characterized as: [19]
Microphytes can be characterized as: [19] [29]
The many possible classifications of aquatic plants are based upon morphology. [5] One example has six groups as follows: [32]
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. [33] This is considered a form of phenotypic plasticity as the plant, once submerged, experiences changes in morphology better suited to their new aquatic environment. [33] However, while some terrestrial plants may be able to adapt in the short-term to an aquatic habitat, it may not be possible to reproduce underwater, especially if the plant usually relies on terrestrial pollinators.
Due to their environment, aquatic plants experience buoyancy which counteracts their weight. [34] Because of this, their cell covering are far more flexible and soft, due to a lack of pressure that terrestrial plants experience. [34] Green algae are also known to have extremely thin cell walls due to their aquatic surroundings, and research has shown that green algae is the closest ancestor to living terrestrial and aquatic plants. [35] 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. [36] [37] 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.
Submerged aquatic plants have more restricted access to carbon as carbon dioxide compared to terrestrial plants. They may also experience reduced light levels. [16] In aquatic plants diffuse boundary layers (DBLs) around submerged leaves and photosynthetic stems vary based on the leaves' thickness, shape and density and are the main factor responsible for the greatly reduced rate of gaseous transport across the leaf/water boundary and therefore greatly inhibit transport of carbon dioxide. [16] To overcome this limitation, many aquatic plants have evolved to metabolise bicarbonate ions as a source of carbon. [16]
Environmental variables affect the instantaneous photosynthetic rates of aquatic plants and the photosynthetic enzymes pigments. [38] 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. [38]
Although most aquatic angiosperms can reproduce by flowering and setting seeds, many have also evolved to have extensive asexual reproduction by means of rhizomes, turions, and fragments in general. [6]
One of the largest aquatic plants in the world is the Bolivian waterlily, which holds the Guinness World Record of having the largest undivided leaf at 3.2 m (10 ft 6 in) diameter; the smallest is the rootless duckweed, which is only 1 mm (0.039 in) across. Many small animals use aquatic plants such as duckweeds and lily pads for spawning or as protective shelters against predators both from above and below the water surface.
Aquatic plants are important primary producers and are the basis of food web for many aquatic fauna, especially wetland species. [39] 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 [40] 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. [41] [25] Historically, aquatic plants have been less studied than terrestrial plants, [42] and management of aquatic vegetation has become an increasingly interested field [43] as means to reduce agricultural pollution of water bodies. [44] [45]
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. [40] Macrophytes are widely used in constructed wetlands around the world to remove excess N and P from polluted water. [46] Beside 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. [47] Macrophytes promote the sedimentation of suspended solids by reducing the current velocities, [48] impede erosion by stabilising soil surfaces. [49] 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. [50]
The additional site-specific macrophytes' value provides wildlife habitat and makes treatment systems of wastewater aesthetically satisfactory. [51]
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 ).
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. [3] Macrophyte levels are easy to sample, do not require laboratory analysis, and are easily used for calculating simple abundance metrics. [3]
Phytochemical and pharmacological researches suggest that freshwater macrophytes, such as Centella asiatica , Nelumbo nucifera , Nasturtium officinale , Ipomoea aquatica and Ludwigia adscendens , are promising sources of anticancer and antioxidative natural products. [52]
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. [53]
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. [51]
The principal factor controlling the distribution of aquatic plants is the availability of water. However, other abiotic factors may also control their distribution including nutrient availability, availability of carbon dioxide and oxygen, water temperature, characteristics of the substrate, water transparency, [54] water movement, and salinity. [8] Some aquatic plants are able to thrive in brackish, saline, and salt water. [5] Also biotic factors like grazing, [8] competition for light, [54] colonization by fungi, [55] and allelopathy [56] are influencing the occurrence of macrophytes.
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. [57] 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 wildlife [58]
Other notable invasive plant species include floating pennywort, [59] Curly leaved pondweed, [58] the fern ally Water fern [58] and Parrot's feather. [60] 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. [58]
In 2012, a comprehensive overview of alien aquatic plants in 46 European countries found 96 alien aquatic species. The aliens were primarily native to North America, Asia, and South America. The most spread alien plant in Europe was Elodea canadensis (Found in 41 European countries) followed by Azolla filiculoides in 25 countries and Vallisneria spiralis in 22 countries. [57] The countries with the most recorded alien aquatic plant species were France and Italy with 30 species followed by Germany with 27 species, and Belgium and Hungary with 26 species. [57]
The European and Mediterranean Plant Protection Organization has published recommendations to European nations advocating the restriction or banning of the trade in invasive alien plants. [61]
The Alismatales (alismatids) are an order of flowering plants including about 4,500 species. Plants assigned to this order are mostly tropical or aquatic. Some grow in fresh water, some in marine habitats. Perhaps the most important food crop in the order is the taro plant, Colocasia esculenta.
Typha is a genus of about 30 species of monocotyledonous flowering plants in the family Typhaceae. These plants have a variety of common names, in British English as bulrush or reedmace, in American English as cattail, or punks, in Australia as cumbungi or bulrush, in Canada as bulrush or cattail, and in New Zealand as reed, cattail, bulrush or raupo. Other taxa of plants may be known as bulrush, including some sedges in Scirpus and related genera.
A wetland is a distinct semi-aquatic ecosystem whose groundcovers are flooded or saturated in water, either permanently, for years or decades, or only seasonally. Flooding results in oxygen-poor (anoxic) processes taking place, especially in the soils. Wetlands form a transitional zone between waterbodies and dry lands, and are different from other terrestrial or aquatic ecosystems due to their vegetation's roots having adapted to oxygen-poor waterlogged soils. They are considered among the most biologically diverse of all ecosystems, serving as habitats to a wide range of aquatic and semi-aquatic plants and animals, with often improved water quality due to plant removal of excess nutrients such as nitrates and phosphorus.
Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be classified by different factors, including temperature, light penetration, nutrients, and vegetation. There are three basic types of freshwater ecosystems: Lentic, lotic and wetlands. Freshwater ecosystems contain 41% of the world's known fish species.
Pistia is a genus of aquatic plants in the arum family, Araceae. It is the sole genus in the tribe Pistieae which reflects its systematic isolation within the family. The single species it comprises, Pistia stratiotes, is often called water cabbage, water lettuce, Nile cabbage, or shellflower. Its native distribution is uncertain but is probably pantropical; it was first scientifically described from plants found on the Nile near Lake Victoria in Africa. It is now present, either naturally or through human introduction, in nearly all tropical and subtropical fresh waterways and is considered an invasive species as well as a mosquito breeding habitat. The specific epithet is derived from a Greek word, στρατιώτης, meaning "soldier", which references the sword-shaped leaves of some plants in the Stratiotes genus.
A constructed wetland is an artificial wetland to treat sewage, greywater, stormwater runoff or industrial wastewater. It may also be designed for land reclamation after mining, or as a mitigation step for natural areas lost to land development. Constructed wetlands are engineered systems that use the natural functions of vegetation, soil, and organisms to provide secondary treatment to wastewater. The design of the constructed wetland has to be adjusted according to the type of wastewater to be treated. Constructed wetlands have been used in both centralized and decentralized wastewater systems. Primary treatment is recommended when there is a large amount of suspended solids or soluble organic matter.
An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic ; lotic ; and wetlands.
A hydrosere is a plant succession which occurs in an area of fresh water such as in oxbow lakes and kettle lakes. In time, an area of open freshwater will naturally dry out, ultimately becoming woodland. During this change, a range of different landtypes such as swamp and marsh will succeed each other.
Luronium natans is a species of aquatic plant commonly known as the floating water-plantain. It is the only recognized species in the genus Luronium, native to western and central Europe, from Spain to Britain to Norway east to Ukraine.
A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems, which include ponds, lakes and wetlands, and much of this article applies to lentic ecosystems in general. Lentic ecosystems can be compared with lotic ecosystems, which involve flowing terrestrial waters such as rivers and streams. Together, these two ecosystems are examples of freshwater ecosystems.
Elodea densa, the large-flowered waterweed or Brazilian waterweed, is a species of Elodea native to warm temperate South America in southeastern Brazil, Argentina, Chile and Uruguay. It is considered a problematic invasive species due to its use in home aquariums and subsequent release into non-native ecosystems.
Nymphoides peltata is perennial, rooted aquatic plant with floating leaves of the family Menyanthaceae.
Potamogeton perfoliatus is a perennial aquatic plant in the family Potamogetonaceae occurring in both standing and flowing freshwater habitats. It is widely distributed globally, occurring in all continents except South America and Antarctica.
Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration of electrolytes to keep the body fluids from becoming too diluted or concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. The higher the osmotic pressure of a solution, the more water tends to move into it. Pressure must be exerted on the hypertonic side of a selectively permeable membrane to prevent diffusion of water by osmosis from the side containing pure water.
Freshwater biology is the scientific biological study of freshwater ecosystems and is a branch of limnology. This field seeks to understand the relationships between living organisms in their physical environment. These physical environments may include rivers, lakes, streams, ponds, reservoirs, or wetlands. Knowledge from this discipline is also widely used in industrial processes to make use of biological processes involved with sewage treatment and water purification. Water presence and flow is an essential aspect to species distribution and influences when and where species interact in freshwater environments.
A freshwater marsh is a non-forested marsh wetland that contains shallow fresh water, and is continuously or frequently flooded. Freshwater marshes primarily consist of sedges, grasses, and emergent plants. Freshwater marshes are usually found near the mouths of rivers, along lakes, or are present in low lying areas with low drainage like abandoned oxbow lakes. Unlike its counterpart the salt marsh, which is regularly flushed with sea water, freshwater marshes receive the majority of their water from surface water.
Landscape limnology is the spatially explicit study of lakes, streams, and wetlands as they interact with freshwater, terrestrial, and human landscapes to determine the effects of pattern on ecosystem processes across temporal and spatial scales. Limnology is the study of inland water bodies inclusive of rivers, lakes, and wetlands; landscape limnology seeks to integrate all of these ecosystem types.
Ludwigia peploides is a species of flowering plant in the evening primrose family known by the common names floating primrose-willow and creeping water primrose. It is native to Australia, North America, and South America, but it can be found on many continents and spreads easily to become naturalized. It is well known as a troublesome aquatic noxious weed that invades water ecosystems and can clog waterways. This is perennial herb which grows in moist to wet to flooded areas. The stem can creep over 2 meters long, sometimes branching. It spreads to form mats on the mud, or floats ascending in the water. The leaves are several centimeters long and are borne in alternately arranged clusters along the stem. The flower has 5 to 6 lance-shaped sepals beneath a corolla of 5 or 6 bright yellow petals up to 2.4 centimeters long. The fruit is a hard, cylindrical capsule.
Aquatic plant management involves the science and methodologies used to control invasive and non-invasive aquatic plant species in waterways. Methods used include spraying herbicide, biological controls, mechanical removal as well as habitat modification. Preventing the introduction of invasive species is ideal.
Typha × glauca is a hybrid species of plant originating as a cross between T. angustifolia and T. latifolia. It shows invasive behavior in the Midwestern United States