mosquito fern
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What is a mosquito fern?
The mosquito fern is any of 6 or 7 species of aquatic ferns belonging to the genus Azolla of the family Salviniaceae. They are found worldwide, particularly in tropical regions, floating on the surface of calm, fresh water or resting on muddy shores.
The name "mosquito fern" comes from the plant's ability to completely cover ponds and other bodies of water, which prevents mosquitoes and other insects from entering the water to lay their eggs. They are grown for their agricultural value and are sometimes used as decorative plants in water gardens.
Azolla is one of the most agriculturally significant ferns. They have been employed as a "super fertilizer" because they contain Anabaena azollae, a cyanobacterium that lives in cavities of the leaves. This bacteria transforms atmospheric nitrogen into nitrate fertilizer. When Azolla plants die, they release nitrate fertilizer into the environment, which other plants can use.
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Where does mosquito fern usually grow?
Mosquito ferns (genus Azolla) are aquatic ferns found worldwide, with the most species diversity in tropical regions. They float on the surface of still, fresh waters and can sometimes be found stranded on muddy banks. Their common name comes from their ability to cover the surface of ponds and other bodies of water, which prevents mosquitoes and other insects from penetrating the water to lay eggs. They are cultivated for agricultural purposes and in water gardens for their ornamental value.
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What does a mosquito fern look like?
The mosquito fern (Azolla) is a tiny aquatic fern with small leaves, often less than 2.5 cm (1 inch) long. Its leaves grow in two alternating rows on either side of its stem and are divided into an upper green lobe and a lower white to transparent lobe.
Azolla maintains a symbiotic relationship with the blue-green alga Anabaena azollae, where the alga provides nitrogen to the fern, and the fern offers a habitat for the alga.
Because of their delicate beauty, mosquito ferns are often used to decorate aquariums and garden pools.
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How does mosquito fern help the environment?
Mosquito ferns help the environment through their agricultural applications. Farmers in Southeast Asia have long known that rice fields with mosquito ferns produce more grain.
Within the mosquito fern's leaves, colonies of cyanobacteria transform atmospheric nitrogen into nitrate fertilizer. When the mosquito ferns die, they release this nitrate fertilizer into the environment, which other plants can then use.
Mosquito ferns can also prevent mosquitoes and other insects from laying eggs by thoroughly covering the surface of ponds and other bodies of water.
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Why is mosquito fern sometimes used in rice fields?
The mosquito fern (Azolla) is often introduced to rice fields because it acts as a natural fertilizer, boosting grain production. Farmers in Vietnam and Southeast Asia have long observed higher rice yields in fields where mosquito ferns are present.
Azolla hosts Anabaena azollae, a cyanobacterium, in its leaves. This bacterium converts atmospheric nitrogen into nitrate, a plant fertilizer. When the mosquito fern dies, it releases this nitrate into the environment, enriching the soil for other plants like rice and taro.
Due to its value as a fertilizer, scientists have developed various Azolla strains to improve nitrogen fixation and distribution. While A. pinnata was initially preferred in Southeast Asia, the American species A. filiculoides has been found to be more disease-resistant with similarly good results.
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What challenges or problems can mosquito fern cause if it grows too much?
Mosquito ferns can be beneficial in agriculture as a natural fertilizer due to their ability to fix nitrogen. They also prevent mosquitoes from laying eggs by covering the water surface. However, excessive growth can cause problems. Dense coverage of mosquito ferns can block sunlight, reducing photosynthesis in other aquatic plants and potentially disrupting the ecosystem.
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mosquito fern, (genus Azolla), genus of six or seven species of aquatic ferns of the family Salviniaceae. Members of Azolla are distributed nearly worldwide but are most diverse in tropical regions. Mosquito ferns float on the surface of still, fresh waters, sometimes becoming stranded on muddy banks. Their name 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. Mosquito ferns are cultivated for their agricultural importance as well as sometimes in water gardens for their ornamental value.
Physical description
Mosquito ferns are very small plants, often less than 2.5 cm (1 inch) long. The tiny leaves are in two alternating rows on either side of the stem and are divided into an upper green lobe and a lower white to transparent lobe. The sporangia (spore-producing structures) are enclosed in small, structurally complex, globose structures known as sporocarps, with separate sporocarps formed containing either numerous microspores or a single megaspore. Both types of spores are globose (tetrahedral), but an average megaspore is 20 or more times larger than a microspore. The highly reduced gametophytes (gamete-producing structures), which develop underwater, are mostly contained within the spore walls.
Agricultural importance
Azolla is one of the most important ferns in agriculture. More money has been spent on its study and more scientific papers have been published involving this genus than on any other fern. Long ago, farmers in Vietnam and other parts of Southeast Asia discovered that rice fields in which mosquito ferns were released produced higher yields of grain. For centuries, families jealously guarded their individual strains of Azolla, keeping them alive in containers between plantings and inoculating the fields at the beginning of each crop cycle.
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The secret behind the use of mosquito fern as a “super fertilizer” is that within cavities of the green upper lobe of the leaves, there live colonies of a cyanobacterium, Anabaena azollae. These photosynthetic bacteria have the ability to transform atmospheric nitrogen into nitrate fertilizer. When individual plants of Azolla die, this nitrate fertilizer is released into the environment, where it becomes available to other plants. In addition to its use in rice fields, Azolla has been shown to benefit the cultivation of some other crops grown in paddies, such as taro. The plants have also been used in livestock and poultry feed.
Scientists have bred numerous strains of Azolla in an effort to increase the efficiency of the nitrogen fixation and distribution cycles. Originally, these were from A. pinnata, the species used in traditional agriculture in Southeast Asia and native to the region. However, in the late 1970s, it was discovered that the American A. filiculoides also yielded good results and was more resistant to various diseases, so strains of this species have also been developed.