Internal links: Monilophytes > Salviniales > Salviniaceae> Azolla filiculoides
External links: Monilophytes > Salviniales > Salviniaceae > Azolla filiculoides
Wikipedia links: Monilophytes > Salviniales > Salviniaceae > Azolla filiculoides
Other links: http://10000thingsofthepnw.com/2021/09/06/azolla-filiculoides/
Species:
Common name: Water fern
Also, mosquito fern, duckweed fern, & fairy moss
Conservation status: unkown
Etymology:
The common name , mosquito fern, is an allusion to the fact that the plants sometimes thoroughly cover the surface of a pond or other body of water, preventing mosquitoes and other insects from penetrating through to the water to lay eggs
The genus is from the Greek azo (to dry), and ollyo (to kill), a reference to the fact that plants are killed by drying out
Spores:
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Leaves:
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Stem & branches:
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Roots:
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Habit:
Aquatic ferns
They are extremely reduced in form and specialized
They look nothing like other typical ferns but more resemble duckweed or some mosses
Habitat:
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Distribution:
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Species:
World:
Australia:
Additional notes:
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 in wetlands, freshwater lakes and ditches
It can alter aquatic ecosystems and biodiversity substantially
Species
Section Rhizosperma
Azolla imbricata
Azolla nilotica Decne. ex Mett.
Azolla pinnata R.Br.
Section Azolla
Azolla cristata Kaulf. (this name takes priority over Azolla caroliniana Willd.)
Azolla filiculoides Lam.
Azolla rubra R.Br.
At least six extinct species are known from the fossil record:
Azolla intertrappea (Eocene, India)
Azolla berryi - Eocene, Green River Formation, Wyoming
Azolla prisca - Oligocene, London Clay, Isle of Wight
Azolla tertiaria - Pliocene, Esmeralda Formation, Nevada
Azolla primaeva - Eocene, Allenby Formation, British Columbia
Azolla boliviensis - Maastrichtian - Paleocene, Eslaboacuten Formation and Flora Formation Bolivia
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 in India
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, an extracellular endosymbiont (living outside the host's cells) which fixes atmospheric 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 in Azolla's cells
The nitrogen-fixing capability of Azolla has led to widespread use as a biofertiliser, 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 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 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 (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 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 2 mm in diameter, and bears numerous male sporangia
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.
Gamopphytes
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 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, 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 FAO study describes how Azolla integrates into a tropical biomass agricultural system, reducing the need for food supplements
Concerns about biomagnification exist because the plant may contain the neurotoxin BMAA that remains present in the bodies of animals consuming it and BMAA has been documented as passing along the food chain
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, 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
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 modality
The proposal draws upon the hypothesized Azolla event that asserts that Azolla once covered the Arctic 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 12–15 °C 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 (Main article: Azolla event)
A study of Arctic 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 to turn into a hot, tropical environment
This research was conducted by the Institute of Environmental Biology at Utrecht University
It indicates that massive patches of Azolla growing on the (then) freshwater surface of the Arctic Ocean consumed enough carbon dioxide from the atmosphere for the global greenhouse effect to decline
Eventually causing the formation of ice sheets in Antarctica and the current "icehouse period"
This theory has been termed the Azolla event
Bioremediation (See also: Bioremediation)
Azolla can remove chromium, nickel, copper, zinc, and lead from effluent
It can also remove lead from solutions containing 1–1000 ppm