Geographic distribution

Azolla occurs naturally in freshwater ditches, ponds, lakes and sluggish rivers of warm-temperate and tropical regions.

Its absence from regions that have prolonged freezing or aridity, both of which are fatal to Azolla, is clearly illustrated by Small & Darbyshire’s (2011) map (below) of its approximate modern distribution.

Modern distribution of Azolla, from Small & Darbyshire (2011)
Approximate modern distribution of Azolla, from Small & Darbyshire (2011)

Lumpkin & Plucknett (1980) suggested that Azolla’s species had the following occurrences prior to their dispersal by humans:

A. caroliniana: eastern North America, and the Caribbean

A. filiculoides: southern South America through western North America and Alaska

A. microphylla: tropical and subtropical America

A. mexicana: northern South America through western North America

A. nilotica: upper reaches of the Nile to Sudan

A. pinnata: most of Asia and the coast of tropical Africa.

According to Scunthorpe (1967), A. filiculoides was formerly native to Europe, where it probably died on during the last ice age. It was re-introduced to Europe in the 19th century, along with A. caroliniana and A. pinnata as ornamentals, but they subsequently spread into the wild.

The distribution of other Azolla species was similarly extended and Lumpkin & Plunkett (1980) recorded the following occurrences for the six Azolla species:

AZOLLA CAROLIANA

Asia: Canton, Hong Kong

Europe: Belgium, Bulgaria, Czechoslovakia, Denmark, France, Germany, Holland, Italy, Romania, Spain

Latin America: Antilles, Argentina, Brazil, Cuba, Guyana, Jamaica, Mexico, Uruguay, Venezuela

North America: Delaware, Florida, Georgia, Kentucky, Maryland, Massachusetts, Nebraska, New Jersey, New York, North Carolina, South Caroline, Tennessee, Texas, Virginia

AZOLLA FILICULOIDES

South Africa

Australia and New Zealand

Asia: China, Japan

Europe: Belgium, Britain, Bulgaria, Czechoslovakia, France, Germany, Holland, Italy, Ireland, Portugal Romania, Sardinia, Yugoslavia

Latin America: Argentina, Bolivia, Brazil, Colombia, Ecuador, Guatemala, Guyana, Honduras, Mexico, Peru, Trinidad, Uruguay

North America: Alaska, Arizona, California, Oregon, Washington

Central Pacific: Hawaii

AZOLLA MEXICANA

Latin America: Bolivia, Costa Rica, Guyana, Honduras, Mexico

North America: British Columbia, California, Illinois, Minnesota, Missouri, Nevada, New Mexico, Oregon, Utah, Washington, Wisconsin

AZOLLA MICROPYLLA

Latin America: Bolivia, Brazil, Dominican Republic, El Salvador, French Guiana, Galapagos Islands, Guyana, Peru

AZOLLA NILOTICA

Africa: Congo, Malawi, Mozambique, Namibia, Sudan, Tanzania, Uganda, Zaire, Zambia

AZOLLA PINNATA

Africa: Angola, Gambia, Ghana, Guinea, Ivory Coast, Madagascar, Mozambique, Namibia, Nigeria, South Africa, Zaire, Zambia

Australia: Australia, New Zealand

Asia: Bangladesh, Burma, China, India, Indonesia, Japan, Korea, Malaysia, Nepal, New Caledonia, New Guinea, Pakistan, Philippines, Sri Lanka, Taiwan, Thailand, Vietnam

ENDEMIC AND INTRODUCED AZOLLA

The distinction between the endemic (original) and ‘introduced’ distribution of Azolla species has important implications for legislation that restricts the sale and use of Azolla species due to their designation as ‘invasive species‘.  Where applied, particularly in Europe, this potentially restricts the use of Azolla to help combat the Perfect Storm: the threats of climate change and shortages of food, land and energy.

In contrast, many other regions, including India and the Far East, have a very different approach to Azolla, using it to produce local biofertilizer and livestock feed.  These utilize an integrated ‘green’ biosystem based on natural relationships between species, rather than increasingly expensive feeds and chemical fertilizers that often have to be transported long distances.

Farmer innoculating a rice paddy with Azolla in the village of La Van, Vietnam.

Farmer inoculating a rice paddy with Azolla in the village of La Van, Vietnam.

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