''Azolla filiculoides'' (water fern) is a species of aquatic fern. It is native to warm temperate and tropical regions of the

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, and has been introduced to

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North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating Direction (geometry), direction or geography. Etymology T ...

and

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Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

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, the

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, and

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. It is a floating aquatic fern with very fast growth, capable of spreading over the surfaces of lakes to give complete coverage of the water in only a few months. Each individual plant is 1–2 cm across, green tinged pink, orange, or red at the edges, branching freely, and breaking into smaller sections as it grows. It is not tolerant of cold temperatures; in temperate regions it largely dies back in winter, surviving by means of submerged buds. It harbors the diazotrophic organism '' Anabaena azollae'' in specialized leaf pockets. This ancient symbiosis allows ''A. azollae'' to fix nitrogen from the air and contribute to the fern's metabolism.

Fossil 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 preserve ...

records from as recent as the last

interglacial An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...

s are known from several locations in Europe (Hyde ''et al.'' 1978). 50 million years ago, a species similar to ''A. filiculoides'' may have played a pivotal role in cooling the planet in what is known as the Azolla event. ''A. filiculoides'' was one of the first two fern species with a reference genome published.

Identification

The only sure method of distinguishing this species from '' A. cristata'' (long incorrectly known as ''A. caroliniana'') is to examine the trichomes on the upper surfaces of the leaves. Trichomes are small protuberances that create water resistance. They are unicellular in ''A. filiculoides'' but septate (two-celled) in ''A. cristata''.

Cultivation

The species has been introduced to many regions of the

Old World The "Old World" () is a term for Afro-Eurasia coined by Europeans after 1493, when they became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia in the Eastern Hemisphere, previously ...

, grown for its

nitrogen-fixing Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

ability that may be used to enhance the growth rate of crops grown in water, such as

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

, or by removal from lakes for use as

green manure In agriculture, a green manure is a crop specifically cultivated to be incorporated into the soil while still green. Typically, the green manure's Biomass (ecology), biomass is incorporated with a plow or disk, as is often done with (brown) man ...

. ''A. filiculoides'' is frequently cultivated in

aquariums An aquarium (: aquariums or aquaria) is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. fishkeeping, Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aquati ...

and

ponds A pond is a small, still, land-based body of water formed by pooling inside a depression, either naturally or artificially. A pond is smaller than a lake and there are no official criteria distinguishing the two, although defining a pond t ...

, where it can become easily dominant over other species.

Invasive species

''A. filiculoides'' was first recorded in Europe in 1870s–1880s, when the species may have been accidentally transported in ballast water, with fry, or directly as an ornamental or aquarium plant. It was introduced into Asia from

East Germany East Germany, officially known as the German Democratic Republic (GDR), was a country in Central Europe from Foundation of East Germany, its formation on 7 October 1949 until German reunification, its reunification with West Germany (FRG) on ...

in 1977 as an alternative to the cold susceptible native strain of '' A. pinnata'', used as a green manure in the rice industry. ''A. filiculoides'' has also been spread around the world as a research model plant for the study of ''Azolla''–'' Anabaena'' symbiosis. In the areas of introduction, ''A. filiculoides'' is capable of rapid growth, especially in eutrophic ecosystems, and outcompetes native aquatic plants. The dense mat of ''A. filiculoides'' causes lack of light penetration and an

anaerobic environment Hypoxia (''hypo'': 'below', ''oxia'': 'oxygenated') refers to low oxygen conditions. Hypoxia is problematic for Aerobic organism, air-breathing organisms, yet it is essential for many Anaerobic organism, anaerobic organisms. Hypoxia applies to m ...

due to

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

decomposition, causing a drastic reduction of

water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...

, aquatic biodiversity, and ecosystem function.

Gallery

Azolla filiculoides0.jpg, Close-up of a leaf Image-IMG 0018Afil.JPG, ''A. filiculoides'' (pink-tinged) with '' Lemna minor'' AzollaFiliculoidesProfilDetail.jpg, Single ''A. filiculoides'' plant showing the roots

References

External links

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Azolla Fern
Project Regeneration *
Flora of North America: ''Azolla filiculoides''USDA Plants Profile: ''Azolla filiculoides''Plants for a Future: ''Azolla filiculoides''NSW Flora Online: ''Azolla filiculoides''
{{Authority control Salviniales Freshwater plants Ferns of Asia Ferns of the Americas Ferns of Australia Ferns of the United States Flora of New South Wales Flora of Queensland Flora of South Australia Flora of Victoria (state) Flora of Tasmania Plants described in 1783 Taxa named by Jean-Baptiste Lamarck