Azolla

Azolla is a tiny plant that floats on water.

It grows very fast. It can double its size in just two days! Some people call it mosquito fern.

This plant helps rice grow. It adds good things to the water. This helps the rice stay healthy.

Sometimes the plant turns bright red. It can look like a red rug on the water.

It is a very busy little plant.

Azolla is a tiny plant that floats on water.

People call it mosquito fern or water fern. It looks more like moss than a normal fern. It grows very fast. It can double its size in less than two days!

This plant has a special partner. It lives with a tiny blue-green germ called Anabaena azollae. This germ stays on the plant. It takes nitrogen from the air and gives it to the plant. This helps the Azolla grow. Farmers in Asia use it to help rice grow. They put it in rice fields. When the plant dies, it lets out nitrogen into the water. This acts as a natural food for the rice.

Azolla can also change the world. Long ago, it may have covered the Arctic. It soaked up a lot of carbon. This might have helped the Earth cool down.

Sometimes, Azolla can be a pest. It can cover a whole pond. This can stop other plants from getting light. It can also make it hard for fish to reach the surface.

Azolla is a very small plant that lives on top of water.

People often call it mosquito fern or water fern. It does not look like most ferns you might see in a forest. Instead, it looks more like tiny moss or duckweed. There are seven different species in this group. One of these is called Azolla filiculoides. This plant is a very fast grower. It can double its size in just 1.9 days. Because it grows so quickly, it can cover the entire surface of a pond.

This plant works with a tiny partner to stay healthy. It has a symbiotic relationship with a blue-green germ called Anabaena azollae. This means the two living things live closely together to help each other. The germ lives outside the cells of the fern. Its special job is to fix nitrogen from the air. This turns the nitrogen into a form the plant can use. The germ is so connected to the fern that it passes from one generation to the next. This partnership helps the Azolla grow very well in many places.

People have used this plant for a very long time. In parts of southeast Asia, farmers use it as a biofertilizer. This is a natural way to help crops grow. Farmers in China have used it for over a thousand years. One old book from 554 CE describes using it in rice paddies. When the Azolla dies, it releases nitrogen into the water. This gives the rice plants the nutrients they need to grow. It can provide up to nine tonnes of protein per hectare every year.

Scientists also look at Azolla to understand the history of Earth. About 55 million years ago, during the Eocene, Azolla may have covered the Arctic. At that time, the Arctic was a warm, tropical place. The huge amount of Azolla soaked up a lot of carbon from the air. This is called carbon sequestration. When the plants sank, they took that carbon with them. Some scientists believe this helped the whole planet cool down. This event may have led to the ice sheets we see in Antarctica today.

Even though it is useful, Azolla can sometimes be a problem. In new places, it can become an invasive species. This happens when a plant spreads too much and causes trouble. Large mats of Azolla can block the sunlight from reaching underwater plants. This makes it hard for those plants to make food. Thick mats can also make it difficult for fish and other animals to reach the surface. Some people use it to control mosquitoes, too. It makes it harder for mosquito larvae to breathe at the surface.

Azolla is a genus of seven aquatic fern species belonging to the family Salviniaceae.

Though they are ferns, they look much more like mosses or duckweeds because they are highly reduced in form. These tiny plants float on the water surface using small, overlapping scale-like leaves. Their roots hang down into the water below. Because they grow so fast, they can change entire aquatic ecosystems. Azolla is a highly productive plant that can double its biomass in just 1.9 days depending on the conditions.

The plant survives through a unique symbiotic relationship with a cyanobacterium called Anabaena azollae. This microorganism lives outside the cells of the host fern. Its primary role is to fix atmospheric nitrogen, turning it into a form the plant can use for growth. This partnership is so deep that the microorganism is transferred directly from one generation of Azolla to the next. In fact, Anabaena azollae is completely dependent on its host. Several of its genes have been lost or transferred into the nucleus of the Azolla cells. This biological connection allows Azolla to thrive even in nutrient-poor environments.

Azolla reproduction involves both sexual and asexual methods. Asexual reproduction occurs when the plant reproduces by splitting. For sexual reproduction, Azolla is heterosporous, meaning it produces two different kinds of spores. During summer, spherical structures called sporocarps form on the undersides of the branches.

The male sporocarp is about two millimeters in diameter and contains many tiny male spores called microspores. The female sporocarp is much smaller and contains one large functional spore called a megaspore. The microspores have barbed structures called glochidia that help them cling to the megaspores for fertilization.

Humans have utilized the nitrogen-fixing power of Azolla for centuries. In southeast Asia, it is widely used as a biofertilizer in rice paddies. Chinese farmers have used it to bolster agricultural productivity for over a thousand years. The earliest written record of this practice appears in the book Qimin Yaoshu, written by Jia Sixie in 554 CE. When farmers flood rice paddies in the spring, they plant Azolla to cover the water and suppress weeds. As the plant material dies and rots, it releases nitrogen into the water. This process can provide up to nine tonnes of protein per hectare every year for the rice crops.

Beyond agriculture, Azolla is being studied for its potential as sustainable livestock feed. It is rich in protein, essential amino acids, vitamins, and minerals. Studies have shown that feeding Azolla to dairy cattle, pigs, ducks, and chickens can increase milk production and weight gain. However, scientists have raised concerns regarding biomagnification. Some studies suggest the plant may contain a neurotoxin called β-methylamino-L-alanine, or BMAA. This substance is linked to neurodegenerative diseases like ALS and Alzheimer's. However, 2024 research suggests the Azolla–Nostoc azollae superorganism does not actually synthesize BMAA or other common cyanotoxins.

Azolla also plays a massive role in the history of Earth's climate. Scientists propose a theory known as the Azolla event. About 55 million years ago during the Eocene, the Arctic was a warm, tropical, freshwater environment. It is believed that Azolla grew so prolifically in the Arctic that it absorbed massive amounts of carbon. When the plants died and sank, they sequestered teratons of carbon. This process likely triggered a global cooling event that lasted to the present. This sequestration may have led to the formation of the ice sheets in Antarctica.

While useful, Azolla can become an invasive species in new environments. In places like the United Kingdom, it can become a pest. The species Azolla filiculoides is especially invasive because it can survive temperatures as low as those allowing thin layers of ice. It can double its surface area or density in 7 to 10 days under ideal conditions. Large mats can cover 100% of a water surface. This prevents underwater plants from photosynthesizing and makes it difficult for fish and amphibians to reach the surface. It can also be used for bioremediation, as it can remove metals like chromium, nickel, copper, zinc, and lead from water.