Could a tiny floating fern be the key to cooling our warming planet?

Gardening · Published 3 October 2026 Swipe more like this →

In short: Azolla, a genus of aquatic ferns, is so efficient at sequestering carbon that it may have triggered a global cooling event 55 million years ago. Today, this fast-growing plant is being studied for its potential in sustainable agriculture, water purification, and as a powerful tool for modern climate mitigation.

Azolla is a highly specialized aquatic fern that thrives through a unique symbiotic relationship with the cyanobacterium Anabaena azollae. Unlike other plants, this partnership is inherited directly from one generation to the next, as the bacteria have integrated into the host's cellular structure. This synergy allows Azolla to fix atmospheric nitrogen with remarkable efficiency, making it a prized biofertilizer. In Asian rice paddies, farmers have utilized this property for over 1,500 years, with records of the practice dating back to Jia Sixie’s 554 CE text, Qimin Yaoshu.

The plant's environmental impact is profound. During the Eocene, massive blooms of Azolla in the Arctic are hypothesized to have sequestered enough carbon to end a period of intense global warming, potentially initiating the current icehouse climate. Today, researchers are investigating whether this mechanism can be replicated for carbon sequestration. Beyond its climate potential, Azolla is a hyper-accumulator capable of removing heavy metals like chromium, nickel, and lead from water, and it is increasingly used as a protein-rich livestock feed.

However, the plant is not without controversy. While often called 'mosquito fern' due to the belief that it prevents mosquitoes from laying eggs, this is a myth; it actually works by physically obstructing larvae from reaching the surface to breathe. Furthermore, while it is a productive crop, concerns exist regarding the presence of neurotoxins like BMAA. Although 2024 studies suggest the Azolla-Nostoc superorganism does not synthesize common cyanotoxins, the potential for biomagnification in the food chain remains a subject of active research. As an invasive species in many regions, Azolla can form dense mats up to 30 centimeters thick, displacing native biodiversity and disrupting aquatic ecosystems by exhausting oxygen levels.

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