Lemnoideae
Encyclopedia
"Duckweed" or "bayroot" are aquatic plants which float on or just beneath the surface of still or slow-moving fresh water bodies. They arose from within the arum or aroid family, (Araceae
), and therefore, often are classified as the subfamily Lemnoideae within the Araceae. Classifications created prior to the approximate end of the twentieth century tend to classify them as a separate family, Lemnaceae.
These plants are very simple, lacking an obvious stem or leaves. They consist of a small 'thalloid' or plate-like structure that floats on or just under the water surface, with or without simple rootlets. The plants are highly reduced from their earlier relatives in Araceae
.
Reproduction is mostly by asexual
budding, but occasionally three tiny 'flowers' consisting of two stamens and a pistil are produced and sexual reproduction
occurs. Some view this 'flower' as a pseudanthium
, or reduced inflorescence
, with three flowers that are distinctly either female or male and which are derived from the spadix
in Araceae
. Anatomical research regarding the mechanics of this process has not been completed or remains ambiguous due to considerable evolutionary reduction of these plants from their earlier relatives. The flower of duckweed genus Wolffia is the smallest known flower in the world, measuring merely 0.3 mm long. The fruit produced through this occasional sexual reproduction is a utricle, and a seed
is produced in a sac containing air that facilitates flotation.
and also is eaten by humans in some parts of Southeast Asia. As it contains more protein than soybeans, it is sometimes cited as a significant potential food source.http://www.journeytoforever.org/edu_pond.html http://web.archive.org/web/20091027041958/http://geocities.com/RainForest/Canopy/3631/
Some duckweed is introduced into freshwater aquarium
s and ponds where they may spread rapidly. This introduction may be deliberate or unintended and once established in a large pond, may be difficult to eradicate. The plant is carried on the feathers, shells, and coats of birds, turtles, reptiles, and aquatic mammals visiting multiple ponds, rivers, and lakes. In water bodies with constant currents or overflow, the plants are carried down the water channels and do not proliferate greatly. In some locations a cyclical pattern driven by weather patterns exists in which the plants proliferate greatly during low water flow periods, then are carried away as rainy periods ensue.
The tiny plants provide cover for fry of many aquatic species. The plants are used as shelter by pond water species such as bullfrog
s and bluegill
s. They also provide shade and, although frequently confused with them, can reduce certain light-generated growths of photoautotrophic algae
.
The plants can provide nitrate
removal, if cropped, and the duckweeds are important in the process of bioremediation
because they grow rapidly, absorbing excess mineral nutrients, particularly nitrogen
and phosphates. For these reasons they are touted as water purifiers of untapped value.
The Swiss Department of Water and Sanitation in Developing Countries, SANDEC, associated with the Swiss Federal Institute for Environmental Science and Technology, asserts that as well as the food and agricultural values, duckweed also may be used for waste water treatment to capture toxins and for odor control, and, that if a mat of duckweed is maintained during harvesting for removal of the toxins captured thereby, it prevents the development of algae and controls the breeding of mosquitoes. http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_wra/downloads_wra/duckweed.pdf The same publication provides an extensive list of references for many duckweed-related topics.
These plants also may play a role in conservation of water because a cover of duckweed will reduce evaporation
of water when compared to the rate of a similar size water body with a clear surface.
it was difficult to test this hypothesis. Starting in 1995 studies began to confirm their placement in the Araceae and since then, most systematists consider them to be part of that family.
Their position within their family has been slightly less clear, but several twenty-first century studies place them in the position shown below. They are not closely related to Pistia
, however, which also is an aquatic plant in the family Araceae.
The genera of duckweeds are: Spirodela
, Landoltia
, Lemna
, Wolffiella
, and Wolffia
.
Duckweed is being studied by researchers around the world as a possible source of clean energy. In the United States, in addition to being the subject of study by the DOE, both Rutgers University and North Carolina State University
have ongoing projects to determine if duckweed might be a source of cost-effective, clean, renewable energy
. Duckweed is a good candidate as a biofuel because as a biomass
it grows rapidly, has 5 to 6 times as much starch as corn, and does not contribute to global warming. Duckweed is considered a carbon neutral energy source, because unlike most fuels, it actually removes carbon dioxide from the atmosphere.
Duckweed also functions as a bioremediator by effectively filtering contaminants such as bacteria, nitrogen, phosphates, and other nutrients from naturally occurring bodies of water, constructed wetlands and waste water.
Turning the canals of the Poitevin Marsh (Marais Poitevin
, France) into the "Green Venice":
Araceae
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 or leaf-like bract. Also known as the Arum family, members are often colloquially...
), and therefore, often are classified as the subfamily Lemnoideae within the Araceae. Classifications created prior to the approximate end of the twentieth century tend to classify them as a separate family, Lemnaceae.
These plants are very simple, lacking an obvious stem or leaves. They consist of a small 'thalloid' or plate-like structure that floats on or just under the water surface, with or without simple rootlets. The plants are highly reduced from their earlier relatives in Araceae
Araceae
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 or leaf-like bract. Also known as the Arum family, members are often colloquially...
.
Reproduction is mostly by asexual
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
budding, but occasionally three tiny 'flowers' consisting of two stamens and a pistil are produced and sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
occurs. Some view this 'flower' as a pseudanthium
Pseudanthium
A pseudanthium or flower head is a special type of inflorescence, in which several flowers are grouped together to form a flower-like structure. The real flowers are generally small and greatly reduced, but can sometimes be quite large...
, or reduced inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
, with three flowers that are distinctly either female or male and which are derived from the spadix
Spadix
In botany, a spadix is a type of spike inflorescence having small flowers borne on a fleshy stem. Spadix are typical of the Family Araceae known as arums or aroids...
in Araceae
Araceae
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 or leaf-like bract. Also known as the Arum family, members are often colloquially...
. Anatomical research regarding the mechanics of this process has not been completed or remains ambiguous due to considerable evolutionary reduction of these plants from their earlier relatives. The flower of duckweed genus Wolffia is the smallest known flower in the world, measuring merely 0.3 mm long. The fruit produced through this occasional sexual reproduction is a utricle, and a seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
is produced in a sac containing air that facilitates flotation.
Duckweed in various environments
Duckweed is an important high-protein food source for waterfowlWaterfowl
Waterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans....
and also is eaten by humans in some parts of Southeast Asia. As it contains more protein than soybeans, it is sometimes cited as a significant potential food source.http://www.journeytoforever.org/edu_pond.html http://web.archive.org/web/20091027041958/http://geocities.com/RainForest/Canopy/3631/
Some duckweed is introduced into freshwater aquarium
Aquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
s and ponds where they may spread rapidly. This introduction may be deliberate or unintended and once established in a large pond, may be difficult to eradicate. The plant is carried on the feathers, shells, and coats of birds, turtles, reptiles, and aquatic mammals visiting multiple ponds, rivers, and lakes. In water bodies with constant currents or overflow, the plants are carried down the water channels and do not proliferate greatly. In some locations a cyclical pattern driven by weather patterns exists in which the plants proliferate greatly during low water flow periods, then are carried away as rainy periods ensue.
The tiny plants provide cover for fry of many aquatic species. The plants are used as shelter by pond water species such as bullfrog
Bullfrog
The American bullfrog , often simply known as the bullfrog in Canada and the United States, is an aquatic frog, a member of the family Ranidae, or “true frogs”, native to much of North America. This is a frog of larger, permanent water bodies, swamps, ponds, and lakes, where it is usually found...
s and bluegill
Bluegill
The Bluegill is a species of freshwater fish sometimes referred to as bream, brim, or copper nose. It is a member of the sunfish family Centrarchidae of the order Perciformes.-Range and distribution:...
s. They also provide shade and, although frequently confused with them, can reduce certain light-generated growths of photoautotrophic algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
.
The plants can provide nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
removal, if cropped, and the duckweeds are important in the process of bioremediation
Bioremediation
Bioremediation is the use of microorganism metabolism to remove pollutants. Technologies can be generally classified as in situ or ex situ. In situ bioremediation involves treating the contaminated material at the site, while ex situ involves the removal of the contaminated material to be treated...
because they grow rapidly, absorbing excess mineral nutrients, particularly nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and phosphates. For these reasons they are touted as water purifiers of untapped value.
The Swiss Department of Water and Sanitation in Developing Countries, SANDEC, associated with the Swiss Federal Institute for Environmental Science and Technology, asserts that as well as the food and agricultural values, duckweed also may be used for waste water treatment to capture toxins and for odor control, and, that if a mat of duckweed is maintained during harvesting for removal of the toxins captured thereby, it prevents the development of algae and controls the breeding of mosquitoes. http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_wra/downloads_wra/duckweed.pdf The same publication provides an extensive list of references for many duckweed-related topics.
These plants also may play a role in conservation of water because a cover of duckweed will reduce evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
of water when compared to the rate of a similar size water body with a clear surface.
Taxonomy
The duckweed have long been a taxonomic mystery, and usually have been considered to be their own family, Lemnaceae. They primarily reproduce asexually. Flowers, if present at all, are small. Roots are either very much reduced, or absent entirely. They were suspected of being related to the Araceae as long ago as 1876, but until the advent of molecular phylogenyMolecular phylogeny
Molecular phylogenetics is the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree...
it was difficult to test this hypothesis. Starting in 1995 studies began to confirm their placement in the Araceae and since then, most systematists consider them to be part of that family.
Their position within their family has been slightly less clear, but several twenty-first century studies place them in the position shown below. They are not closely related to Pistia
Pistia
Pistia is a genus of aquatic plant in the arum family, Araceae. The single species it comprises, Pistia stratiotes, is often called water cabbage, water lettuce, or Nile cabbage. Its native distribution is uncertain, but probably pantropical; it was first described from the Nile near Lake Victoria...
, however, which also is an aquatic plant in the family Araceae.
The genera of duckweeds are: Spirodela
Spirodela
Spirodela is a genus of aquatic plant. It is 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....
, Landoltia
Landoltia punctata
Spirodela punctata is a species of duckweed . 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...
, Lemna
Lemna
Lemna is a genus of free-floating aquatic plants from the duckweed family. These rapidly-growing plants have found uses as a model system for studies in community ecology, basic plant biology, in ecotoxicology, in production of biopharmaceuticals, and as a source of animal feeds for agriculture...
, Wolffiella
Wolffiella
Wolffiella is a genus of aquatic plants commonly called duckweeds in the Araceae family. Common names for plants in this genus include bogmat and mud-midget. They are rootless and have a keel that allows them to maintain their orientation in the water...
, and Wolffia
Wolffia
Wolffia is a genus of 9 to 11 species which include the smallest flowering plants on Earth. Commonly called watermeal or duckweed, these aquatic plants resemble specks of cornmeal floating on the water. Wolffia species are free-floating thalli, green or yellow-green, and without roots. The flower...
.
Research
In July 2008 the U.S. Department of Energy (DOE) Joint Genome Institute announced that the Community Sequencing Program would fund sequencing of the genome of the giant duckweed, Spirodela polyrhiza. This was a priority project for DOE in 2009. The research is intended to facilitate new biomass and bio-energy programs.Duckweed is being studied by researchers around the world as a possible source of clean energy. In the United States, in addition to being the subject of study by the DOE, both Rutgers University and North Carolina State University
North Carolina State University
North Carolina State University at Raleigh is a public, coeducational, extensive research university located in Raleigh, North Carolina, United States. Commonly known as NC State, the university is part of the University of North Carolina system and is a land, sea, and space grant institution...
have ongoing projects to determine if duckweed might be a source of cost-effective, clean, renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...
. Duckweed is a good candidate as a biofuel because as a biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
it grows rapidly, has 5 to 6 times as much starch as corn, and does not contribute to global warming. Duckweed is considered a carbon neutral energy source, because unlike most fuels, it actually removes carbon dioxide from the atmosphere.
Duckweed also functions as a bioremediator by effectively filtering contaminants such as bacteria, nitrogen, phosphates, and other nutrients from naturally occurring bodies of water, constructed wetlands and waste water.
Turning the canals of the Poitevin Marsh (Marais Poitevin
Marais Poitevin
The Marais Poitevin is a large area of marshland in Western France, a remnant of the former Gulf of Poitou...
, France) into the "Green Venice":
External links
- The Charms of Duckweed by John W. Cross.
- Wayne Armstrong's treatment of the Lemnaceae and allies
- Lemnaceae in Watson, L. and M.J. Dallwitz (1992 onwards). The families of flowering plants: descriptions, illustrations, identification, information retrieval. Version: 3 May 2006. http://delta-intkey.com
- The Duckweed Genome Project