Lemna | |
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Common duckweed (Lemna minor) | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Angiosperms |
Clade: | Monocots |
Order: | Alismatales |
Family: | Araceae |
Subfamily: | Lemnoideae |
Genus: | Lemna L. |
Synonyms [1] [2] | |
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Lemna is a genus of free-floating aquatic plants referred to by the common name "duckweed". They are morphologically divergent members of the arum family Araceae. These rapidly growing plants have found uses as a model system for studies in community ecology, basic plant biology, ecotoxicology, and production of biopharmaceuticals, and as a source of animal feeds for agriculture and aquaculture. Currently, 14 species of Lemna are recognised. [3]
These duckweeds were previously placed in a separate flowering plant family, the Lemnaceae, but they are now considered to be members of the Araceae. [4]
Lemna species grow as simple free-floating thalli on or just beneath the water surface. Most are small, not exceeding 5 mm in length, except Lemna trisulca , which is elongated and has a branched structure. Lemna thalli have a single root, which distinguishes this genus from the related genera Wolffia (lacks roots), Spirodela and Landoltia (have multiple roots).
The plants grow mainly by vegetative reproduction: two daughter plants bud off from the adult plant. This form of growth allows very rapid colonisation of new water. Duckweeds are flowering plants, and nearly all of them are known to reproduce sexually, flowering and producing seed under appropriate conditions. Certain duckweeds (such as L. gibba) are long-day plants, while others (such as L. minor) are short-day plants.
When Lemna invades a waterway, it can be removed mechanically, by the addition of herbivorous fish (e.g. grass carp), or, inadvisedly, treated with a herbicide.
The rapid growth of duckweeds finds application in bioremediation of polluted waters, in municipal wastewater treatment [5] and as test organisms for environmental studies. [6] It is also being used as an expression system for economical production of complex biopharmaceuticals.
Duckweed meal (dried duckweed) is a good cattle feed. It contains 25–45% protein (depending on the growth conditions), 4.4% fat, and 8–10% fibre, measured by dry weight.
Organisation for Economic Co-operation and Development [7] and U.S. Environmental Protection Agency (US EPA) [8] guidelines describe toxicity testing using L. gibba or L. minor as test organisms. Both of these species have been studied extensively for use in phytotoxicity tests. Genetic variability in responses to toxicants can occur in Lemna, and data are insufficient to recommend a specific clone for testing. The US EPA test uses aseptic technique. The OECD test is not conducted axenically, but steps are taken at stages during the test procedure to keep contamination by other organisms to a minimum. Depending on the objectives of the test and the regulatory requirements, testing may be performed with renewal (semistatic and flow-through) or without renewal (static) of the test solution. Renewal is useful for substances that are rapidly lost from solution as a result of volatilisation, photodegradation, precipitation, or biodegradation.
Lemna has been transformed by molecular biologists to express proteins of pharmaceutical interest. Expression constructs were engineered to cause Lemna to secrete the transformed proteins into the growth medium at high yield. Since the Lemna is grown on a simple medium, this substantially reduces the burden of protein purification in preparing such proteins for medical use, promising substantial reductions in manufacturing costs. [9] [10] In addition, the host Lemna can be engineered to cause secretion of proteins with human patterns of glycosylation, an improvement over conventional plant gene-expression systems. [11] Several such products are being developed, including monoclonal antibodies.
High yields of duckweed with a high protein content for use in human nutrition, animal and fish feed can be achieved by careful control of growth conditions. Although duckweed can tolerate temperatures ranging from 6 °C (43 °F) to 33 °C (91 °F), the optimal growth range is 20 °C (68 °F) to 28 °C (82 °F). The acceptable pH range is 5 to 9, but better growth is obtained in the pH range of 6.5 to 7.5. A minimum water depth of 1 foot (30 cm) is desirable to prevent excessive temperature swings. High nitrogen levels, for example 20 mM urea, have provided a protein content in the range of 45% by dry weight. The water may typically contain 60 mg/L of soluble nitrogen and 1 mg/L of phosphorus. Fertiliser is required on a daily basis for optimal growth.
Duckweed can be farmed organically, with nutrients being supplied from a variety of sources, for example human urine, [12] cattle manure, pig waste, biogas plant slurry, or other organic matter in slurry form. Because of the rapid growth of duckweed, daily harvesting is necessary to achieve optimal yields. Harvesting is done such that less than 1 kg/m2 of duckweed remains. Under optimal conditions, a duckweed farm can produce 10 to 30 tons of dried duckweed per hectare per year. [13]
Infrageneric classification following Les et al. 2002. [14]
The Araceae are a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe. Also known as the arum family, members are often colloquially known as aroids. This family of 140 genera and about 4,075 known species is most diverse in the New World tropics, although also distributed in the Old World tropics and northern temperate regions.
Crotalaria is a genus of flowering plants in the family Fabaceae commonly known as rattlepods. The genus includes over 700 species of herbaceous plants and shrubs. Africa is the continent with the majority of Crotalaria species, which are mainly found in damp grassland, especially in floodplains, depressions and along edges of swamps and rivers, but also in deciduous bush land, roadsides and fields. Some species of Crotalaria are grown as ornamentals. The common name rattlepod or rattlebox is derived from the fact that the seeds become loose in the pod as they mature, and rattle when the pod is shaken. The name derives from the Ancient Greek κρόταλον, meaning "castanet", and is the same root as the name for the rattlesnakes (Crotalus).
Spirodela is a genus of aquatic plants, one of several genera containing plants commonly called duckweed. Spirodela species are members of the Araceae under the APG II system. They were formerly members of the Lemnaceae.
This article gives an overview of the aquatic communities in the British National Vegetation Classification system.
Spirodela punctata is a species of duckweed (Lemnoideae). The species is morphologically intermediate between Lemna and other species of Spirodela. In 1999 D.H. Les and D.J. Crawford proposed segregating the species to a new genus Landoltia containing just the species L. punctata, on the basis of biochemical and DNA studies.
Wolffia is a genus of aquatic plants with a cosmopolitan distribution. They include the smallest flowering plants on Earth. Commonly called watermeal or duckweed, these aquatic plants resemble specks of cornmeal floating on the water. Individuals often float together in pairs or form floating mats with related plants, such as Lemna and Spirodela species.
Lemna minor, the common duckweed or lesser duckweed, is a species of aquatic freshwater plant in the subfamily Lemnoideae of the arum family Araceae. L. minor is used as animal fodder, bioremediator, for wastewater nutrient recovery, and other applications.
Joachim Wilhelm "Jo" Messing was a German-American biologist who was a professor of molecular biology and the fourth director of the Waksman Institute of Microbiology at Rutgers University.
Cataclysta lemnata, the small china-mark, is a moth species of the family Crambidae. It is found in Europe, Morocco and Iran.
The Sifton Bog Environmentally Significant Area is a wetland jointly administered by the city of London, Ontario and the Upper Thames River Conservation Authority. It is located west of Hyde Park Road and south of Oxford Street inside the city limits of London, Southern Ontario, Canada. It is a Class 2 provincially significant wetland.
Spirodela polyrhiza is a species of duckweed known by the common names common duckmeat, greater duckweed, great duckmeat, common duckweed, and duckmeat. It can be found nearly worldwide in many types of freshwater habitat.
Wolffia arrhiza is a species of flowering plant known by the common names spotless watermeal and rootless duckweed, belonging to the Araceae, a family rich in water-loving species, such as Arum and Pistia. It is the smallest vascular plant on Earth. It is native to Europe, Africa, and parts of Asia, and it is present in other parts of the world as a naturalized species.
Wolffia globosa is a species of flowering plant known by the common names Asian watermeal and duckweed. It is native to Asia and is found in parts of the Americas and Africa, where it is an introduced species. It grows in mats on the surface of calm, freshwater bodies, such as ponds, lakes, and marshes. It is a very tiny, oval-shaped plant with no leaves, stems, or roots. The body of the plant, a transparent green frond, is less than a millimeter wide. In one human experiment, processed W. globosa was reported to provide dietary protein and vitamin B12.
Scirpus ancistrochaetus is a rare species of flowering plant in the sedge family known by the common names barbedbristle bulrush and northeastern bulrush. It is native to the northeastern United States from New Hampshire south to Virginia. It used to be found in Quebec but it is now thought to be extirpated there. It was also believed extirpated from the state of New York, but at least one population has been rediscovered in Steuben County in 2010. It is threatened by the loss and degradation of its wetland habitat. It is a federally listed endangered species.
Lemnoideae is a subfamily of flowering aquatic plants, known as duckweeds, water lentils, or water lenses. They float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands. Also known as bayroot, they arose from within the arum or aroid family (Araceae), so often are classified as the subfamily Lemnoideae within the family Araceae. Other classifications, particularly those created prior to the end of the twentieth century, place them as a separate family, Lemnaceae.
Lemna turionifera is a species of flowering plant belonging to the family Araceae.
Elaine Munsey Tobin is a professor of molecular, cell, and developmental biology at the University of California, Los Angeles (UCLA). Tobin is recognized as a Pioneer Member of the American Society of Plant Biologists (ASPB).
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