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Water Fern

Azolla filiculoides

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Plant Profile

Salviniaceae (Water Fern)
Life Cycle:
Annual or Perennial
Maximum Size:
2 centimetres tall
Ditches, marshes, ponds, water.
Water Fern (Azolla filiculoides), despite being commonly referred to as a fern, does not produce traditional flowers. Instead, it reproduces through spores, like other ferns. Azolla filiculoides has tiny, scale-like leaves that float on the water surface, forming a dense mat. These leaves are bright green but can turn reddish or purplish under high sunlight or in colder weather. The plant's reproductive structures are microscopic and contained in specialized structures called sporocarps. Thus, the beauty of Azolla filiculoides lies in its lush, mat-forming foliage rather than in any floral display.
Water Fern does not produce traditional fruits. Instead, it reproduces through spores contained in specialized structures known as sporocarps. These sporocarps are tiny, often less than a millimeter in size, and are typically found on the undersides of the leaves. The sporocarps house both male and female spores, facilitating reproduction when conditions are favorable. The reproductive strategy of Azolla filiculoides, relying on spores rather than flowers and fruits, is typical of ferns and contributes to its ability to rapidly colonize water surfaces.
The leaves of Water Fern are small, scale-like, and arranged in overlapping pairs along the plant's slender, branching stems. Each leaf is typically around 1-2 millimeters in length. The upper surface of the leaves is green, but they can turn reddish or purplish in high sunlight or cold temperatures. The leaves have a unique, almost quilted appearance due to their water-repellent, finely divided structure, which helps the plant float on the water's surface. Beneath the surface, root-like structures hang down, further aiding in the plant's buoyancy and nutrient absorption from the water.
Water Fern does not have a distinct scent that is notable to human senses. Unlike some flowering plants that may emit fragrances to attract pollinators, Azolla filiculoides does not produce flowers or emit any discernible aroma. Its main characteristics lie in its aquatic habitat adaptation, rapid growth, and reproductive strategy rather than olfactory appeal. Therefore, encountering Water Fern typically involves observing its dense mat of floating foliage rather than detecting any specific scent.
Other Names:
Azolla, Fairy Fern, Fairy Moss, Mosquito Fern, Pacific Mosquitofern, Water Velvet.
Frequency (UK):
Occasionally seen  

Other Information


Azolla filiculoides, also known as fairy moss, water velvet, or mosquito fern, is a species of small floating aquatic fern that is native to North America, as well as parts of Europe, Asia, and Africa. It is a small plant that typically grows to be about 1-2 inches tall and wide. The fronds of Azolla filiculoides are finely divided, and it forms a dense mat of bright green foliage on the surface of still or slow-moving water bodies such as ponds, marshes, and ditches.

The plant has a symbiotic relationship with a blue-green algae, Anabaena azollae, which lives within the plant's leaves and provides it with nitrogen. Azolla filiculoides is often used to control mosquitoes, because of its dense growth habit and ability to outcompete other aquatic plants that mosquitoes use as breeding sites.

It is also useful as a green manure, as a nutrient-rich plant that can be incorporated into the soil to improve fertility and soil health. Some farmers use it as a natural fertilizer, it is also used as a food source for livestock and can be used to make biofertilizer.

This plant is considered as an invasive species in some parts of the world, because of its ability to outcompete native aquatic plants, it can quickly cover the surface of ponds and slow-moving water bodies and make it difficult for other aquatic plants to survive. This can also lead to a decline in aquatic wildlife that depends on native plants for habitat.

This plant can be easily propagated from small fragments and is widely available commercially. It can also be easily grown in gardens and backyard ponds.


Water Fern, also known as Azolla filiculoides, is a unique aquatic plant that has captured the interest of scientists and horticulturists alike. This small, free-floating fern has gained attention for its ability to remove excess nutrients from water, making it an effective tool for water purification. In this blog, we'll explore the fascinating characteristics of Water Fern and its potential benefits.

Azolla filiculoides is native to the Americas, Europe, and parts of Asia. It grows in still or slow-moving bodies of water, such as ponds, lakes, and wetlands. Water Ferns are very small, with leaves ranging in size from 1 to 2 cm. The plant has a distinctive green color and a feathery appearance due to its branching fronds.

One of the most remarkable aspects of Water Fern is its symbiotic relationship with a nitrogen-fixing cyanobacterium called Anabaena azollae. This bacterium lives inside the fern's leaves and converts atmospheric nitrogen into a form that the plant can use. As a result, Water Ferns can thrive in nitrogen-poor environments and can even improve the soil quality of surrounding land when they decompose.

Water Ferns are also useful for water purification. The plant's ability to remove excess nutrients, such as nitrogen and phosphorus, from water has been studied extensively. In some studies, Water Ferns have been shown to remove up to 97% of nitrogen and 78% of phosphorus from wastewater. This makes them an effective tool for reducing the negative impact of nutrient pollution on aquatic ecosystems.

In addition to its environmental benefits, Water Ferns have also been used in traditional medicine. In China, the plant is commonly used to treat a variety of ailments, including fever, jaundice, and hemorrhoids. Research has shown that Water Ferns contain compounds with anti-inflammatory and antioxidant properties, which may explain their therapeutic effects.

Water Ferns are easy to cultivate and can be grown in a range of aquatic environments, from small fish tanks to large-scale wastewater treatment facilities. They can be used in conjunction with other water treatment methods, such as biofilters or wetlands, to enhance their effectiveness. The plant is also attractive and can be used in ornamental water gardens.

Water Ferns have been studied extensively for their potential use in sustainable agriculture. They have been shown to be a valuable source of organic matter, nitrogen, and other nutrients that can be used to enrich soil and enhance crop growth. In some countries, Water Ferns have been used as a green manure crop, which is a practice of using plants to improve soil fertility. As the plant decomposes, it releases nutrients back into the soil, enriching it for future crops.

Another interesting characteristic of Water Ferns is their ability to survive extreme environmental conditions. They are capable of surviving in temperatures ranging from 0°C to 30°C and can tolerate low oxygen levels. This makes them an ideal plant for use in areas prone to flooding or other natural disasters. In some regions of the world, Water Ferns have been used as a survival food during times of drought or famine.

Water Ferns are also important for biodiversity conservation. They provide a habitat for a range of aquatic organisms, including insects, snails, and small fish. They are also a food source for some animals, such as ducks and geese. In some areas, Water Ferns have been used to create artificial wetlands, which can provide a habitat for a range of plant and animal species.

However, Water Ferns can also be invasive in some regions. Their ability to grow quickly and form dense mats can displace native vegetation and reduce biodiversity. In areas where they are considered invasive, Water Ferns should be controlled to prevent their spread.

Water Ferns have also shown potential in other areas such as bioenergy production. Their fast growth and high nitrogen content make them a promising candidate for use as a feedstock for biofuel production. In fact, some research has shown that Water Ferns have a higher biomass yield and a better quality of biofuel than other common feedstocks such as corn or soybeans.

Moreover, Water Ferns are being explored for their potential in phytoremediation, which is the use of plants to remove contaminants from the environment. They have been shown to be effective in removing heavy metals such as lead, cadmium, and arsenic from contaminated soil and water. This makes them a promising plant for use in contaminated land reclamation and the restoration of polluted water bodies.

Water Ferns also have cultural and historical significance in some regions. In ancient China, Water Ferns were used to feed silkworms, and the ferns themselves were used as a source of green dye for clothing. In Japan, Water Ferns are still used in traditional cuisine and are considered a delicacy.

Finally, the genome of Azolla filiculoides has been sequenced, which will help researchers better understand the plant's unique characteristics and its potential uses. This will open up new opportunities for research and development of new applications.

In conclusion, Water Ferns are a remarkable plant that offers a range of benefits, from water purification to sustainable agriculture and bioenergy production. They have cultural and historical significance, and their potential in phytoremediation is promising. With continued research and development, Water Ferns may prove to be an important tool for solving some of the world's most pressing environmental and agricultural challenges.

30 Water Fern Facts

Here are 30 facts about Water Fern (Azolla filiculoides):

  1. Water Fern belongs to the genus Azolla and is also known as Pacific Mosquito Fern.
  2. It is a small aquatic fern native to the Americas but has spread globally.
  3. Azolla filiculoides forms dense mats on the surface of still or slow-moving freshwater.
  4. The plant's small, scale-like leaves are green but can turn reddish under certain conditions.
  5. It reproduces via spores contained in specialized structures called sporocarps.
  6. Water Fern lacks traditional roots but has fine root-like structures that hang in the water.
  7. It is often used in agriculture as a biofertilizer due to its ability to fix nitrogen from the atmosphere.
  8. Water Fern can double its biomass in 3–10 days under optimal conditions.
  9. This fern has been used traditionally in some cultures as animal fodder, particularly for poultry and fish.
  10. Azolla filiculoides has a symbiotic relationship with a nitrogen-fixing cyanobacterium, Anabaena azollae.
  11. It has a long history, with fossil records dating back over 75 million years.
  12. The plant is highly efficient at removing heavy metals from polluted water.
  13. Water Fern can be invasive in some regions where it outcompetes native aquatic plants.
  14. In Asia, Water Fern has been traditionally used as a green manure in rice paddies.
  15. It has a high protein content, making it a potential source of sustainable protein.
  16. Azolla filiculoides can survive in a wide range of temperatures, from tropical to temperate zones.
  17. The fern provides habitat and food for various aquatic organisms, including insects and small fish.
  18. Its rapid growth can contribute to the eutrophication of water bodies if not managed properly.
  19. Water Fern has been studied for its potential use in wastewater treatment and bioremediation.
  20. It played a role in climate change millions of years ago by absorbing atmospheric carbon dioxide.
  21. The plant's ability to reduce evaporation from water bodies makes it useful in water conservation efforts.
  22. Water Fern's floating mats can hinder recreational activities like boating and fishing.
  23. It has been used experimentally in space research due to its ability to thrive in microgravity.
  24. The fern is a natural habitat for certain mosquito larvae species.
  25. Azolla filiculoides can alter the pH and nutrient levels of water bodies it colonizes.
  26. Its leaves are water-repellent, helping the plant stay buoyant on the water surface.
  27. In some cultures, Water Fern has medicinal uses for ailments like jaundice and ulcers.
  28. The plant's nitrogen-fixing ability enhances soil fertility when used as a green manure.
  29. Water Fern can be controlled through mechanical removal or with herbicides in invasive situations.
  30. Studying Azolla filiculoides aids in understanding plant adaptation to aquatic environments and symbiotic relationships with microorganisms.

These facts highlight the diverse ecological, agricultural, and potential industrial applications of Water Fern (Azolla filiculoides).

Distribution Map

Reproduced by kind permission of the BSBI.

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