''Azolla filiculoides'' (water fern) is a species of ''

Azolla ''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 rese ...

'', native to warm temperate and tropical regions of the

Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with t ...

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 The order Salviniales (formerly known as the Hydropteridales and including the former Marsileales) is an order of ferns in the class Polypodiopsida. Description Salviniales are all aquatic and differ from all other ferns in being heterosporous, ...

, 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 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 ''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'' (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, or by removal from lakes for use as green manure. ''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 ''Lemna minor'', the common duckweed or lesser duckweed, is a species of aquatic freshwater plant in the subfamily Lemnoideae of the arum family Araceae. ''L. minor'' is used as animal fodder, bioremediator, for wastewater nutrient recovery, and ...

'' 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