''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 Hawaii. It is a floating aquatic fern, with very fast growth, capable of spreading over lake surfaces 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 and, in temperate regions it largely dies back in winter, surviving by means of submerged buds. It harbors the diazotrophic organism, '' Nostoc azollae'', in specialized leaf pockets. This ancient symbiosis allows ''N. 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 preserved ...

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 ...

s are known from several locations in

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

(Hyde ''et al.'' 1978). 50 million years ago, a species similar to ''Azolla filiculoides'' may have played a pivotal role in cooling the planet. ''Azolla filiculoides'' was one of the first two fern species for which a reference genome has been published.

Identification

The only sure method of distinguishing this species from ''

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, ...

'' (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, grown for its nitrogen-fixing ability that may be used to enhance the growth rate of crops grown in water, such as

rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly '' Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and ''Porteresia'', both wild and domestica ...

, or by removal from lakes for use as

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

. ''A. filiculoides'' is frequently cultivated in aquariums and ponds, 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 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 outcompete native aquatic plants. The dense mat of ''A. filiculoides'' causes lack of light penetration and an anaerobic environment due to detritus decomposition, causing a drastic reduction of water quality, aquatic biodiversity and ecosystem funcion.

Gallery

Azolla filiculoides0.jpg, Close-up of a leaf Image-IMG 0018Afil.JPG, ''A. filiculoides'' (pink-tinged) with '' Lemna minor'' AzollaFiliculoidesProfilDetail.jpg, Single ''Azolla 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''
{{Taxonbar, from=Q2705087 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 (Australia) Flora of Tasmania Plants described in 1783 Taxa named by Jean-Baptiste Lamarck