''Azolla'' (mosquito fern, duckweed fern, fairy moss, water fern) is a
genus of seven species of
aquatic ferns in the family
Salviniaceae
Salviniaceae (), is a family of heterosporous ferns in the order Salviniales. The Salviniaceae contain the two genera ''Azolla'' and '' Salvinia'', with about 20 known species in total. The oldest records of the family date to the Late Cretaceou ...
. 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 f ...
or some
mosses. ''
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 t ...
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'') le ...
substantially.
Species
Section ''Rhizosperma''
*''
Azolla imbricata''
*''
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. 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 Heidelb ...
*''
Azolla pinnata
''Azolla pinnata'' is a species of fern known by several common names, including mosquitofern, feathered mosquitofern and water velvet. It is native to much of Africa, Asia (Brunei Darussalam, China, India, Japan, Korea, and the Philippines) and ...
''
R.Br.
Section ''Azolla''
*''
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. (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.)
*''
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 ...
''
Lam.
*''
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 ...
''
R.Br.
: Sources:
At least six
extinct 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 ...
:
*''
Azolla intertrappea''
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 ...
& H.S. Rao, 1934 (
Eocene,
India)
*''
Azolla berryi''
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,
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 f ...
,
Wyoming)
*''
Azolla prisca''
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), Austral ...
, 1926 (
Oligocene,
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 ...
,
Isle of Wight)
*''
Azolla tertiaria''
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,
Esmeralda Formation,
Nevada)
*''
Azolla primaeva''
( Penhallow) Arnold
Arnold may refer to:
People
* Arnold (given name), a masculine given name
* Arnold (surname), a German and English surname
Places Australia
* Arnold, Victoria, a small town in the Australian state of Victoria
Canada
* Arnold, Nova Scotia
U ...
, 1955 (
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)
*''
Azolla boliviensis''
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 r ...
, 2005 (
Maastrichtian -
Paleocene,
Eslaboacuten Formation and
Flora Formation 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 ...
)
Ecology
''Azolla'' is a highly
productive plant. It can double its
biomass 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
''Azolla pinnata'' is a species of fern known by several common names, including mosquitofern, feathered mosquitofern and water velvet. It is native to much of Africa, Asia (Brunei Darussalam, China, India, Japan, Korea, and the Philippines) and ...
'' 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 ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
, with their roots hanging in the
water. 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 parasi ...
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 ...
''
Anabaena azollae'', an extracellular
endosymbiont (living outside the host's cells) which
fixes 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. The typical limiting factor on its growth is
phosphorus; thus, an abundance of phosphorus - due for example to
eutrophication 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
Nucl ...
in Azolla's cells.
The nitrogen-fixing capability of ''Azolla'' has led to widespread use as a
biofertiliser
A biofertilizer is a substance which contains living micro-organisms which, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of prim ...
, especially in parts of
southeast Asia. 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 per hectare per year.
''Azolla'' are
weeds 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",
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 mouthp ...
feeding induces accumulation of deoxyanthocyanins and leads to a reduction in the proportion of
polyunsaturated fatty 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 also not tolerant of
salinity; 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. It is a common native aquatic plant in
Tasmania. 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, ...
formation, but unlike other members of this group ''Azolla'' is
heterosporous, 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 cy ...
. Male spores (microspores) are extremely small and are produced inside each
microsporangium
Microsporangia are sporangia that produce microspores that give rise to male gametophytes when they germinate. Microsporangia occur in all vascular plants that have heterosporic life cycles, such as seed plants, spike mosses and the aquatic fer ...
. 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 gametophy ...
.
''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, ...
s. The female gametophyte 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 gametophy ...
and bears a small number of archegonia, 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 t ...
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 t ...
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. ''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 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 properties ...
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, an ...
, 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 ...
.
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 in the early 17th century, ''Azolla''’s use as a green compost was documented in local records.
Larvicide
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". ''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 lan ...
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 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 (Greenland), Finland, Iceland, N ...
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, 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 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 (Greenland), Finland, Iceland, N ...
paleoclimatology reported that ''Azolla'' may have had a significant role in reversing an increase in greenhouse effect 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 Magn ...
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 enrollm ...
. 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 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 L ...
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 ...
and the current "icehouse period". This theory has been termed the 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, copper, zinc, and lead from effluent. It can also remove lead from solutions containing 1–1000 ppm.
References
External links
The Azolla Foundation: ''Azolla'' Non-Profit Information & Guidance Website
* ttp://waynesword.palomar.edu/plnov98.htm Marriage Between A Fern & Cyanobacterium
NSW Flora online: ''Azolla''
{{Taxonbar, from=Q1128633
Aquatic plants
Extant Maastrichtian first appearances
Fern genera
Invasive plant species in Japan
Klondike Mountain Formation
Maastrichtian genus first appearances
Nitrogen-fixing crops
Salviniales
Taxa named by Jean-Baptiste Lamarck