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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, fields, gardens, ponds, water.
Ferns do not have flowers. They reproduce by spores, not flowers.
The fruit of ferns are spores.
Water Fern is often mistaken for a Duckweed. It carpets the surface of still fresh water. It has large feathery duckweed-like fronds. The fronds overlap along the stems. Bluish-green, later becoming red. Perennial.
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.

Distribution Map

Reproduced by kind permission of the BSBI.

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