''Azolla'' (mosquito fern, duckweed fern, fairy moss, water fern) is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
fern
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...
s in the family
Salviniaceae
Salviniaceae (), is a family of heterosporous ferns in the order Salviniales. The Salviniaceae contain the two genera ''Azolla'' and ''Salvinia
''Salvinia'', a genus in the family Salviniaceae, is a floating fern named in honor of Anton Ma ...
. They are extremely reduced in form and specialized, looking nothing like other typical ferns but more resembling
duckweed
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 ...
or some
moss
Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...
es. ''
Azolla filiculoides
''Azolla filiculoides'' (water fern) is a species of ''Azolla'', native to warm temperate and tropical regions of the Americas which was introduced to Europe, North and sub-Saharan Africa, China, Japan, New Zealand, Australia, the Caribbean and H ...
'' is one of just two fern species for which a reference genome has been published. It is believed that this genus grew so prolifically during the Eocene (and thus absorbed such a large amount of carbon) that it triggered a global cooling event that has lasted to the present.
Azolla is considered an
invasive plant
An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
in
wetlands
A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...
,
freshwater lake
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
s and ditches. It can alter
aquatic ecosystem
An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The tw ...
s and
biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
substantially.
Species
Section ''Rhizosperma''
*''
Azolla imbricata
''Azolla'' (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like other typical ferns but more res ...
''
*''
Azolla nilotica
''Azolla nilotica'' is a medium-sized floating fern, that naturally occurs in the Nile and in eastern and central Africa. It is assigned to the family Salviniaceae.
Description
''Azolla nilotica'' is a floating water-bound fern of up to long ...
''
Decne.
Joseph Decaisne (7 March 1807 – 8 January 1882) was a French botanist and agronomist. He became an ''aide-naturaliste'' to Adrien-Henri de Jussieu (1797-1853), who served as the chair of rural botany. It was during this time that he began to stu ...
ex
Mett.
Georg Heinrich Mettenius (24 November 1823 – 18 August 1866) was a German botanist born in Frankfurt am Main. He was son-in-law to botanist Alexander Braun (1805–1877).
In 1845 he received his medical doctorate from the University of Heidelbe ...
Azolla cristata
''Azolla cristata '', the Carolina mosquitofern, Carolina azolla or water velvet, 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, an ...
''
Kaulf.
Georg Friedrich Kaulfuss (8 April 1786 – 9 December 1830) was a professor at Halle. He described the pteridophytes collected by Adelbert von Chamisso, and he named the fern ''Cibotium chamissoi'' after him. The genus ''Kaulfussia'' is name ...
(this name takes priority over ''
Azolla caroliniana
''Azolla cristata '', the Carolina mosquitofern, Carolina azolla or water velvet, 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, an ...
''
Willd.
Carl Ludwig Willdenow (22 August 1765 – 10 July 1812) was a German botanist, pharmacist, and plant taxonomist. He is considered one of the founders of phytogeography, the study of the geographic distribution of plants. Willdenow was al ...
)
*''
Azolla filiculoides
''Azolla filiculoides'' (water fern) is a species of ''Azolla'', native to warm temperate and tropical regions of the Americas which was introduced to Europe, North and sub-Saharan Africa, China, Japan, New Zealand, Australia, the Caribbean and H ...
Azolla rubra
''Azolla rubra,'' known commonly as red azolla and Pacific azolla is a species of fern native to Australia and New Zealand. In New Zealand, it may also be known by its Māori names , , and .
Distribution
''Azolla rubra'' is found in Australia ...
extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
species are known from the
fossil record
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
Sahni Sahni (alternatively Sawhney, Sahney, Shahani , or Sahani ) is an Indian (Khatri) surname found among the Hindus or Sikhs of Punjab.
Notable people with the surname include:
* Ajai Sahni, author and expert on counter-terrorism
* Ajay Prakash S ...
& H.S. Rao, 1934 (
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
,
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
Brown
Brown is a color. It can be considered a composite color, but it is mainly a darker shade of orange. In the CMYK color model used in printing or painting, brown is usually made by combining the colors orange and black. In the RGB color model used ...
, 1934 (
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
,
Green River Formation
The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The sediments are deposited in very fine ...
,
Wyoming
Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...
Chandler
Chandler or The Chandler may refer to:
* Chandler (occupation), originally head of the medieval household office responsible for candles, now a person who makes or sells candles
* Ship chandler, a dealer in supplies or equipment for ships
Arts ...
&
Reid
Reid is a surname of Scottish origin. It means "red".
People with the surname
* Alan Reid (disambiguation)
* Alex Reid (disambiguation), includes Alexander Reid
* Amanda Reid, Australian Paralympic athlete
* Amanda Reid (taxonomist), Australia ...
, 1926 (
Oligocene
The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
,
London Clay
The London Clay Formation is a marine geological formation of Ypresian (early Eocene Epoch, c. 56–49 million years ago) age which crops out in the southeast of England. The London Clay is well known for its fossil content. The fossils from t ...
,
Isle of Wight
The Isle of Wight ( ) is a county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the largest and second-most populous island of England. Referred to as 'The Island' by residents, the Isle of ...
Berry
A berry is a small, pulpy, and often edible fruit. Typically, berries are juicy, rounded, brightly colored, sweet, sour or tart, and do not have a stone or pit, although many pips or seeds may be present. Common examples are strawberries, raspb ...
, 1927 (
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Esmeralda Formation,
Nevada
Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
,
Allenby Formation
The Allenby formation is a sedimentary rock formation in British Columbia which was deposited during the Ypresian stage of the Early Eocene. It consists of conglomerates, sandstones with interbedded shales and coal. The shales contain an abun ...
,
British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
Vajda
Vajda is a Hungarian language surname. It is derived from Proto-Slavic *vojevoda. In medieval times, vajda was the equivalent of voivode, meaning a "war-leader" or "war-lord". The name may refer to:
* Anna Vajda (born 1984), Hungarian basketball ...
&
McLoughlin
McLoughlin is one of nearly two dozen Anglicisms for three Gaelic-Irish surnames: Mac/Nic Lochlainn (most commonly Anglicised ''McLaughlin''), Ó/Ní Maoilsheachlainn (usually ''McLoughlin'' or ''M'Loughlin''), and Mac/Nic Lochnaigh (usually ren ...
, 2005 (
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
-
Paleocene
The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...
Bolivia
, image_flag = Bandera de Bolivia (Estado).svg
, flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center
, flag_alt2 = 7 × 7 square p ...
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
in as little as 1.9 days, depending on growing conditions, and yield can reach 8–10 tonnes fresh matter/ha in Asian rice fields. 37.8 t fresh weight/ha (2.78 t DM/ha dry weight) has been reported for '' Azolla pinnata'' in India (Hasan et al., 2009).
''Azolla'' floats on the surface of water by means of numerous small, closely overlapping scale-like
leaves
A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
, with their roots hanging in the
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
. They form a
symbiotic
Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...
relationship with the
cyanobacterium
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue ...
endosymbiont
An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.
(The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within" ...
atmospheric
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
. The typical limiting factor on its growth is
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
; thus, an abundance of phosphorus - due for example to
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
or chemical runoff - often leads to ''Azolla'' blooms. Unlike all other known plants, its symbiotic microorganism transfers directly from one generation to the next. ''A. azollae'' is completely dependent on its host, as several of its genes have either been lost or transferred to the
nucleus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
*Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucle ...
in Azolla's cells.
The nitrogen-fixing capability of ''Azolla'' has led to widespread use as a biofertiliser, especially in parts of
southeast Asia
Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...
. The plant has been used to bolster agricultural productivity in China for over a thousand years. When
rice paddies
A paddy field is a flooded field of arable land used for growing semiaquatic crops, most notably rice and taro. It originates from the Neolithic rice-farming cultures of the Yangtze River basin in southern China, associated with pre-Aust ...
are flooded in the spring, they can be planted with ''Azolla'', which then quickly multiplies to cover the water, suppressing weeds. The rotting plant material resulting from the die off of this ''Azolla'' releases nitrogen into the water for the rice plants, providing up to nine tonnes of
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
per hectare per year.
''Azolla'' are
weed
A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place", or a plant growing where it is not wanted.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. ...
s in many parts of the world, entirely covering some bodies of water. The myth that no
mosquito
Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...
can penetrate the coating of fern to lay its eggs in the water gives the plant its common name "mosquito fern", and may deter the survival of some of the larvae.
Most species can produce large amounts of deoxyanthocyanins in response to various stresses, including bright sunlight and extreme temperatures, causing the water surface to appear to be covered with an intensely red carpet.
Herbivore
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
feeding induces accumulation of deoxyanthocyanins and leads to a reduction in the proportion of
polyunsaturated fat
Polyunsaturated fats are fats in which the constituent hydrocarbon chain possesses two or more carbon–carbon double bonds. Polyunsaturated fat can be found mostly in nuts, seeds, fish, seed oils, and oysters. "Unsaturated" refers to the fact tha ...
ty acids in the
fronds
A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...
, thus lowering their palatability and nutritive value.
''Azolla'' cannot survive winters with prolonged freezing, so is often grown as an
ornamental plant
Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that i ...
at high latitudes where it cannot establish itself firmly enough to become a weed. It is also not tolerant of
salinity
Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...
; normal plants cannot survive in greater than 1–1.6‰, and even conditioned organisms die if grown in water with a salinity above 5.5‰.
''Azolla filiculoides''
''Azolla filiculoides'' (red azolla) is the only member of this genus and of the family Azollaceae in
Tasmania
)
, nickname =
, image_map = Tasmania in Australia.svg
, map_caption = Location of Tasmania in AustraliaCoordinates:
, subdivision_type = Country
, subdi ...
. It is a common native aquatic plant in
Tasmania
)
, nickname =
, image_map = Tasmania in Australia.svg
, map_caption = Location of Tasmania in AustraliaCoordinates:
, subdivision_type = Country
, subdi ...
. It is common behind farm dams and other still waterbodies. The plants are small (usually only a few cm across) and float, but they are fast growing, and can be abundant and form large mats. The plants are typically red, and have small, water repellent leaves.
Reproduction
''Azolla'' reproduces sexually, and asexually (by splitting).
Like all ferns, sexual reproduction leads to
spore
In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
formation, but unlike other members of this group ''Azolla'' is
heterosporous
Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these, the microspore, is male and the larger megaspore is female. Heterospory evolved during the Devonian period from is ...
, producing spores of 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 bears numerous male
sporangia
A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cyc ...
. Male spores (microspores) are extremely small and are produced inside each microsporangium. 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
Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These plants have two spore types, megaspores and microspores. Generally speaking, the megaspore, or large spore, germinates into a female gamet ...
.
''Azolla'' has microscopic male and female gametophytes that develop inside the male and female
spore
In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
s. The female
gametophyte
A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...
protrudes from the
megaspore
Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These plants have two spore types, megaspores and microspores. Generally speaking, the megaspore, or large spore, germinates into a female gamet ...
and bears a small number of
archegonia
An archegonium (pl: archegonia), from the ancient Greek ''ἀρχή'' ("beginning") and ''γόνος'' ("offspring"), is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female ga ...
, each containing a single egg. The microspore forms a male gametophyte with a single
antheridium
An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also ...
which produces eight swimming sperm. The barbed
glochidia
The glochidium (plural glochidia) is a microscopic larval stage of some freshwater mussels, aquatic bivalve mollusks in the families Unionidae and Margaritiferidae, the river mussels and European freshwater pearl mussels.
These larvae are ...
on the male spore clusters cause them to cling to the female megaspores, thus facilitating fertilization.
Applications
Food and animal feed
In addition to its traditional cultivation as a bio-fertilizer for wetland paddies, ''Azolla'' is finding increasing use for sustainable production of
livestock feed
Fodder (), also called provender (), is any agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food given to the animals (includin ...
. ''Azolla'' is rich in protein, essential amino acids, vitamins, and minerals. Studies describe feeding ''Azolla'' to
dairy cattle
Dairy cattle (also called dairy cows) are cattle bred for the ability to produce large quantities of milk, from which dairy products are made. Dairy cattle generally are of the species ''Bos taurus''.
Historically, little distinction was mad ...
, pigs, ducks, and chickens, with reported increases in
milk production
A dairy is a business enterprise established for the harvesting or processing (or both) of animal milk – mostly from cows or buffaloes, but also from goats, sheep, horses, or camels – for human consumption. A dairy is typically located on ...
, weight of broiler chickens and egg production of layers, as compared to conventional feed. One
FAO
The Food and Agriculture Organization of the United Nations (FAO)french: link=no, Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is an intern ...
study describes how ''Azolla'' integrates into a tropical biomass agricultural system, reducing the need for food supplements. Concerns about
biomagnification
Biomagnification, also known as bioamplification or biological magnification, is any concentration of a toxin, such as pesticides, in the tissues of tolerant organisms at successively higher levels in a food chain. This increase can occur as a ...
exist because the plant may contain the neurotoxin
BMAA
β-Methylamino--alanine, or BMAA, is a non-proteinogenic amino acid produced by cyanobacteria. BMAA is a neurotoxin and its potential role in various neurodegenerative disorders is the subject of scientific research.
Structure and properti ...
that remains present in the bodies of animals consuming it and BMAA has been documented as passing along the
food chain
A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), det ...
. ''Azolla'' may contain this substance that is a possible cause of neurodegenerative diseases. ''Azolla'' has been suggested as a foodstuff for human consumption, however, no long-term studies of the safety of eating ''Azolla'' have been made on humans. Previous studies attributed neurotoxin production to ''Anabaena flos-aquae'' species, which is also a type of nitrogen-fixing cyanobacteria. Further research may be needed to ascertain if ''A. azollae'' produces neurotoxins.
Companion plant
''Azolla'' has been used for at least one thousand years in rice paddies as a
companion plant
Companion planting in gardening and agriculture is the planting of different crops in proximity for any of a number of different reasons, including pest control, pollination, providing habitat for beneficial insects, maximizing use of space, and ...
, to fix nitrogen and to block out light to prevent competition from other plants. Rice is planted when tall enough to poke through the ''Azolla'' layer. Mats of mature ''Azolla'' can also be used as a weed-suppressing
mulch
A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area.
A m ...
.
Rice farmers used ''Azolla'' as a rice biofertilizer 1500 years ago. The earliest known written record of this practice is in a book written by Jia Ssu Hsieh (Jia Si Xue) in 540 A.D on ''The Art of Feeding the People'' (Chih Min Tao Shu). By the end of the
Ming dynasty
The Ming dynasty (), officially the Great Ming, was an Dynasties in Chinese history, imperial dynasty of China, ruling from 1368 to 1644 following the collapse of the Mongol Empire, Mongol-led Yuan dynasty. The Ming dynasty was the last ort ...
in the early 17th century, ''Azolla''’s use as a green compost was documented in local records.
Larvicide
The myth that no
mosquito
Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...
can penetrate the coating of fern to lay its eggs in the water gives the plant its common name "mosquito fern". ''Azolla'' have been used to control mosquito larvae in rice fields. The plant grows in a thick mat on the surface of the water, making it more difficult for the larvae to reach the surface to breathe, effectively choking the larvae.
Climate change
Azolla has been proposed as a
carbon sequestration
Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land ...
modality. The proposal draws upon the hypothesized
Azolla event
The Azolla event is a scenario hypothesized to have occurred in the middle Eocene epoch, around , when blooms of the freshwater fern ''Azolla'' are thought to have happened in the Arctic Ocean. As they sank to the stagnant sea floor, over a per ...
that asserts that Azolla once covered the
Arctic
The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...
and then sank, permanently sequestering teratons of carbon that would otherwise have contributed to the planet's greenhouse effect and ending a warming event that reached degrees warmer than twenty-first century averages.
They contribute significantly to decreasing the atmospheric CO2 levels.
Invasive species
This fern has been introduced to other parts of the world, including the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
, where it has become a pest in some areas. A nominally tropical plant, it has adapted to the colder climate. It can form mats up to 30 cm thick and cover 100% of a water surface, preventing local insects and amphibians from reaching the surface.
Importance in paleoclimatology
A study of
Arctic
The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...
paleoclimatology
Paleoclimatology (British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to ...
reported that ''Azolla'' may have had a significant role in reversing an increase in
greenhouse effect
The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...
that occurred 55 million years ago that had caused the region around the
north pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface. It is called the True North Pole to distinguish from the Mag ...
to turn into a hot, tropical environment. This research was conducted by the Institute of Environmental Biology at
Utrecht University
Utrecht University (UU; nl, Universiteit Utrecht, formerly ''Rijksuniversiteit Utrecht'') is a public research university in Utrecht, Netherlands. Established , it is one of the oldest universities in the Netherlands. In 2018, it had an enrollme ...
. It indicates that massive patches of ''Azolla'' growing on the (then) freshwater surface of the
Arctic Ocean
The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...
consumed enough
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
from the atmosphere for the global greenhouse effect to decline, eventually causing the formation of
ice sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at Las ...
s in
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
Azolla event
The Azolla event is a scenario hypothesized to have occurred in the middle Eocene epoch, around , when blooms of the freshwater fern ''Azolla'' are thought to have happened in the Arctic Ocean. As they sank to the stagnant sea floor, over a per ...
.
Bioremediation
''Azolla'' can remove
chromium
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
Chromium metal is valued for its high corrosion resistance and hardne ...
,
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...
,
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
,
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
, and
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
from effluent. It can also remove lead from solutions containing 1–1000 ppm.