Mosquito fern
Encyclopedia
Azolla is a genus
of seven species of aquatic
fern
s in the family Salviniaceae
. They are extremely reduced in form and specialized, looking nothing like conventional ferns but more resembling duckweed or some moss
es.
Willd.
[ Poss. synon. of A. filiculoides ]
Azolla circinata Oltz & Hall
Azolla filiculoides
Lam.
Azolla japonica Franch. & Sav.
[ Poss. synon. of A. filiculoides ]
Azolla mexicana C.Presl
Azolla microphylla Kaulf.
Azolla nilotica Decne. ex Mett.
Azolla pinnata
R.Br.
Azolla rubra R.Br.
[ Poss. synon. of A. filiculoides ]
At least six extinct species are known from the fossil record:
Azolla filiculoides (Red Azolla)
Azolla filiculoides (Red Azolla) is the only member of this genus and of the family Azollaceae in Tasmania. It is a very common native aquatic plant in Tasmania. It is particularly common on farm dams and other still water bodies. The plants are small (usually only a few cm across) and float, but can be very abundant and form large mats. The plants are typically red, and have very small water repellent leaves.'Azolla floats on the surface of water by means of numerous, small, closely overlapping scale-like leaves, with their roots hanging in the water
. They form a symbiotic
relationship with the cyanobacterium Anabaena azollae
, which fixes
atmospheric nitrogen
, giving the plant access to the essential nutrient
. This has led to the plant being dubbed a "super-plant", as it can readily colonise areas of freshwater, and grow at great speed - doubling its biomass every two to three days. The only known limiting factor on its growth is phosphorus
, another essential mineral. An abundance of phosphorus, due for example to eutrophication
or chemical runoff, often leads to Azolla blooms.
The nitrogen-fixing capability of Azolla has led to Azolla being widely used as a biofertiliser, especially in parts of southeast Asia
. Indeed, the plant has been used to bolster agricultural productivity in China for over a thousand years. When rice
paddies are flooded in the spring, they can be inoculated with Azolla, which then quickly multiplies to cover the water, suppressing weeds. The rotting plant material releases nitrogen to the rice plants, providing up to nine tonnes of protein per hectare per year.
Azolla are also serious weed
s in many parts of the world, entirely covering some bodies of water. The myth that no mosquito
can penetrate the coating of fern to lay its eggs in the water gives the plant its common name "mosquito fern".
Most of the species can produce large amounts of deoxyanthocyanin
s in response to various stresses, including bright sunlight and extremes of temperature, causing the water surface to appear to be covered with an intensely red carpet. Herbivore feeding induces accumulation of deoxyanthocyanins and leads to a reduction in the proportion of polyunsaturated fat
ty acids in the fronds, thus lowering their palatability and nutritive value.
Azolla cannot survive winters with prolonged freezing, so is often grown as an ornamental plant
at high latitudes where it cannot establish itself firmly enough to become a weed. It is not tolerant to salinity; normal plants can't survive in greater than 1-1.6‰, and even conditioned organisms die in over 5.5‰ salinity.
Azolla reproduces sexually, and asexual
ly by splitting.
Like all ferns, sexual reproduction leads to spore
formation, but Azolla sets itself apart from other members of its group by producing two kinds. During the summer months, numerous spherical structures called sporocarps
form on the undersides of the branches. The male sporocarp is greenish or reddish and looks like the egg mass of an insect or spider. It is two millimeters in diameter, and inside are numerous male sporangia. Male spores (microspores) are extremely small and are produced inside each microsporangium. Curiously, microspores tend to adhere in clumps called massulae.
Female sporocarps are much smaller, containing one sporangium and one functional spore. Since an individual female spore is considerably larger than a male spore, it is termed a megaspore
.
Azolla has microscopic male and female gametophytes that develop inside the male and female spores. The female gametophyte
protrudes from the megaspore and bears a small number of archegonia, each containing a single egg. The microspore forms a male gametophyte with a single antheridium which produces eight swimming sperm. The barbed glochidia on the male spore clusters are assumed to cause them to cling to the female megaspores, thus facilitating fertilization.
study describes how azolla integrates into a tropical biomass agricultural system, reducing the need for inputs.
A study of Arctic
climatology reported that azolla may have had a significant role in reversing an increase in greenhouse effect
that occurred 55 million years ago that caused the region around the north pole to turn into a hot tropical environment. This research conducted by the Institute of Environmental Biology at Utrecht University
claims that large dense patches of Azolla growing around freshwater lakes formed by the climate change eventually consumed enough carbon dioxide
for the greenhouse effect to reverse.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of seven species of aquatic
Aquatic plant
Aquatic plants are plants that have adapted to living in aquatic environments. 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...
fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s in the family Salviniaceae
Salviniaceae
Salviniaceae , is a family of ferns....
. They are extremely reduced in form and specialized, looking nothing like conventional ferns but more resembling duckweed or some moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
es.
Selected species
Azolla carolinianaAzolla caroliniana
Azolla caroliniana is a species of Azolla native to the Americas, in eastern North America from southern Ontario southward, and from the east coast west to Wisconsin and Texas, and in the Caribbean, and in Central and South America from southeastern Mexico south to northern Argentina and...
Willd.
[ Poss. synon. of A. filiculoides ]
Azolla circinata Oltz & Hall
Azolla filiculoides
Azolla filiculoides
Azolla filiculoides is a species of Azolla, native to warm temperate and tropical regions of the Americas as well as most of the old world including Asia and Australia....
Lam.
Azolla japonica Franch. & Sav.
[ Poss. synon. of A. filiculoides ]
Azolla mexicana C.Presl
Azolla microphylla Kaulf.
Azolla nilotica Decne. ex Mett.
Azolla pinnata
Azolla pinnata
Azolla pinnata is a species of fern known by several common names, including feathered mosquitofern and water velvet. It is native to much of Africa, Asia from China to Japan, India and the Philippines, and parts of Australia. It is an aquatic plant, its frond floating upon the surface of the water...
R.Br.
Azolla rubra R.Br.
[ Poss. synon. of A. filiculoides ]
- List sources :
At least six extinct species are known from the fossil record:
- Azolla intertrappea SahniBirbal SahniBirbal Sahni FRS was an Indian paleobotanist who studied the fossils of the Indian subcontinent, was also a geologist who took an interest in archaeology...
& H.S. Rao, 1934 (EoceneEoceneThe Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
, IndiaIndiaIndia , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
) - Azolla berryi Brown, 1934 (EoceneEoceneThe Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
, Green River FormationGreen River FormationThe Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in winter. Each pair of layers is called a varve and...
, WyomingWyomingWyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
) - Azolla prisca Chandler & Reid, 1926 (OligoceneOligoceneThe Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, London ClayLondon ClayThe London Clay Formation is a marine geological formation of Ypresian age which crops out in the southeast of England. The London Clay is well known for the fossils it contains. The fossils from the Lower Eocene indicate a moderately warm climate, the flora being tropical or subtropical...
, Isle of WightIsle of WightThe Isle of Wight is a county and the largest island of England, located in the English Channel, on average about 2–4 miles off the south coast of the county of Hampshire, separated from the mainland by a strait called the Solent...
) - Azolla tertiaria BerryEdward W. BerryEdward Wilber Berry was an American paleontologist and botanist, the principal focus of his research was paleobotany. Berry studied North and South American flora and published taxonomic studies with theoretical reconstructions of paleoecology and phytogeography. He started his scientific...
, 1927 (PliocenePlioceneThe Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
, Esmeralda Formation, NevadaNevadaNevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
) - Azolla primaevaAzolla primaevaAzolla primaeva is an extinct species of "water fern" in the Azollaceae family known from Eocene fossils from the Ypresian stage , found in southern British Columbia....
(PenhallowDavid P. PenhallowDavid Pearce Penhallow was a Canadian-American botanist, paleobotanist and educator.Born in Kittery Point, Maine, Penhallow graduated from Massachusetts Agricultural College in 1873 . When his former professor, William S...
) ArnoldChester A. ArnoldChester Arthur Arnold was an American paleobotanist, born June 25, 1901 in Leeton, Missouri and died on 19 November 1977.He was the son of farmers Elmer and Edith Arnold. Arnolds family moved to Ludlowville, New York and he attended Cornell University with the intent to study agriculture...
, 1955 (EoceneEoceneThe Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
, Allenby Formation, British ColumbiaBritish ColumbiaBritish Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
) - Azolla boliviensis Vajda & McLoughlin, 2005 (MaastrichtianMaastrichtianThe Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
- PaleocenePaleoceneThe Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
, Eslaboacuten Formation& Flora Formation Bolvia)
Ecology
'DescriptionAzolla filiculoides (Red Azolla)
Azolla filiculoides (Red Azolla) is the only member of this genus and of the family Azollaceae in Tasmania. It is a very common native aquatic plant in Tasmania. It is particularly common on farm dams and other still water bodies. The plants are small (usually only a few cm across) and float, but can be very abundant and form large mats. The plants are typically red, and have very small water repellent leaves.'Azolla floats on the surface of water by means of numerous, small, closely overlapping scale-like leaves, with their roots hanging in the water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. They form a symbiotic
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
relationship with the cyanobacterium Anabaena azollae
Anabaena
Anabaena is a genus of filamentous cyanobacteria that exists as plankton. It is known for its nitrogen fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern. They are one of four genera of cyanobacteria that produce neurotoxins, which are harmful to...
, which fixes
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
atmospheric 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...
, giving the plant access to the essential nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
. This has led to the plant being dubbed a "super-plant", as it can readily colonise areas of freshwater, and grow at great speed - doubling its biomass every two to three days. The only known limiting factor on its growth is phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, another essential mineral. An abundance of phosphorus, due for example to eutrophication
Eutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...
or chemical runoff, often leads to Azolla blooms.
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
. Indeed, the plant has been used to bolster agricultural productivity in China for over a thousand years. When rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
paddies are flooded in the spring, they can be inoculated with Azolla, which then quickly multiplies to cover the water, suppressing weeds. The rotting plant material releases nitrogen to the rice plants, providing up to nine tonnes of protein per hectare per year.
Azolla are also serious weed
Weed
A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...
s in many parts of the world, entirely covering some bodies of water. The myth that no mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
can penetrate the coating of fern to lay its eggs in the water gives the plant its common name "mosquito fern".
Most of the species can produce large amounts of deoxyanthocyanin
Anthocyanin
Anthocyanins are water-soluble vacuolar pigments that may appear red, purple, or blue according to pH...
s in response to various stresses, including bright sunlight and extremes of temperature, causing the water surface to appear to be covered with an intensely red carpet. Herbivore feeding induces accumulation of deoxyanthocyanins and leads to a reduction in the proportion of polyunsaturated fat
Polyunsaturated fat
In nutrition, polyunsaturated fat, or polyunsaturated fatty acid, are fatty acids in which more than one carbon–carbon double bond exists within the representative molecule. That is, the molecule has two or more points on its structure capable of supporting hydrogen atoms not currently part of the...
ty acids in the fronds, thus lowering their palatability and nutritive value.
Azolla cannot survive winters with prolonged freezing, so is often grown as an ornamental plant
Ornamental plant
Ornamental plants are plants that are grown for decorative purposes in gardens and landscape design projects, as house plants, for cut flowers and specimen display...
at high latitudes where it cannot establish itself firmly enough to become a weed. It is not tolerant to salinity; normal plants can't survive in greater than 1-1.6‰, and even conditioned organisms die in over 5.5‰ salinity.
Reproduction
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...
ly by splitting.
Like all ferns, sexual reproduction leads to spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
formation, but Azolla sets itself apart from other members of its group by producing two kinds. During the summer months, numerous spherical structures called sporocarps
Sporocarp (ferns)
A sporocarp is a specialised type of structure found in some ferns whose primary function is the production and release of spores.Among ferns, sporocarps are found only in the three families of the order Salviniales, a group that is both aquatic and heterosporous. The term actually refers to two...
form on the undersides of the branches. The male sporocarp is greenish or reddish and looks like the egg mass of an insect or spider. It is two millimeters in diameter, and inside are numerous male sporangia. Male spores (microspores) are extremely small and are produced inside each microsporangium. Curiously, microspores tend to adhere in clumps called massulae.
Female sporocarps are much smaller, containing one sporangium and one functional spore. Since an individual female spore is considerably larger than a male spore, it is termed a megaspore
Megaspore
Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These types of plants have two spore types, megaspores and microspores. Generally speaking, the megaspore, or large spore, germinates into a female gametophyte, which is fertilized by sperm produced...
.
Azolla has microscopic male and female gametophytes that develop inside the male and female spores. The female gametophyte
Gametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
protrudes from the megaspore and bears a small number of archegonia, each containing a single egg. The microspore forms a male gametophyte with a single antheridium which produces eight swimming sperm. The barbed glochidia on the male spore clusters are assumed to cause them to cling to the female megaspores, thus facilitating fertilization.
Food
In addition to its traditional cultivation as a bio-fertilizer for wetland paddy (due to its ability to fix nitrogen), azolla is finding increasing use for sustainable production of livestock feed. Azolla is rich in proteins, essential amino acids, vitamins and minerals. Studies describe feeding azolla to dairy cattle, pigs, ducks, and chickens, with reported increases in milk production, weight of broiler chickens and egg production of layers, as compared to conventional feed. One FAOFão
Fão is a town in Esposende Municipality in Portugal....
study describes how azolla integrates into a tropical biomass agricultural system, reducing the need for inputs.
Companion plant
Azolla has been used, for at least one thousand years http://www.dhakai.com/botany/Keynote%20paper.pdf, in rice paddies as a companion plant, because of its ability to both fix nitrogen, and block out light to prevent any competition from other plants, aside from the rice, which is planted when tall enough to poke out of the water through the azolla layer.Larvicide
As an additional benefit to its role as a paddy biofertilizer, Azolla spp. have been used to control mosquito larvae in rice fields. The plant grows in a thick mat on the surface of the water, reducing the rate at which oxygen dissolves into the water, effectively choking the larvae.Climatic paleontology
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
climatology reported that azolla may have had a significant role in reversing an increase in greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...
that occurred 55 million years ago that caused the region around the north pole to turn into a hot tropical environment. This research conducted by the Institute of Environmental Biology at Utrecht University
Utrecht University
Utrecht University is a university in Utrecht, Netherlands. It is one of the oldest universities in the Netherlands and one of the largest in Europe. Established March 26, 1636, it had an enrollment of 29,082 students in 2008, and employed 8,614 faculty and staff, 570 of which are full professors....
claims that large dense patches of Azolla growing around freshwater lakes formed by the climate change eventually consumed enough carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
for the greenhouse effect to reverse.