If you ever watch a duck float across a pond, gobbling up the vegetation coating the surface, that bird is way ahead of its time. The buoyant greenery is azolla, a tiny fern that grows like crazy, doubling its biomass as quickly as every two days to conquer small bodies of water. The duck doesn’t know it—and who could blame it, really—but azolla may soon spread across human civilization, becoming food for people and livestock, fertilizer for crops, and even biofuel.
“I’m not out here saying everybody should go eat this stuff right away,” says research technologist Daniel Winstead, who’s studying azolla at Penn State. “There’s a lot of work that needs to be done. But boy, it’s got so much potential.”
The main reason you wouldn’t want to go scoop some azolla out of a pond and eat it duck-style is, first of all, yuck. But also, previously studied species of azolla are typically high in polyphenols, a family of compounds found in many types of plant. In small quantities, polyphenols act as antioxidants, meaning they help remove certain harmful substances from the body. But in azolla quantities, polyphenols may interfere with the body’s ability to absorb nutrients. At such levels, not only are they not nutritious, they’re anti-nutritious.
But there’s a species—Carolina azolla, native to the southeastern United States—that doesn’t have this drawback. Testing for polyphenolic content, Winstead found this azolla to have much, much lower levels than other species, actually more in line with the mainstay fruits and vegetables Americans eat. And when Winstead prepared Carolina azolla in three different ways—fermentation, boiling, and pressure cooking—he found this reduced the polyphenolic content still further, by 62, 88, and 92 percent, respectively. (According to chefs, azolla is “crisp and juicy,” tasting “somewhat of earth, metal, minerals, mushrooms, moss, and grass.”)
This, Winstead believes, could be the key to making azolla a common food worldwide. “You could use those cooking methods on these other species of azolla from Asia,” says Winstead, who described the findings in a recent paper. “That would reduce polyphenol content to a level that was not limiting.”
Compared to other vegetables, Carolina azolla is high in zinc, manganese, iron, calcium, and potassium, and is relatively high in protein (though has less than a grain like barley). And that’s from wild azolla. “Wheat, rice, barley, soybeans—all these things have been domesticated and cultivated, choosing for attributes like nutrition,” says Winstead. “So just imagine if people did that for azolla, if you could create an azolla strain that creates a whole bunch of precursors for biodiesel. You could create another one that creates tons of protein.”
Again, Winstead isn’t suggesting that anyone go out and harvest their local pond for azolla. But with further research, azolla has the potential to become a more extensively cultivated crop, especially if scientists can breed it to express even more nutrients. They’ll also need to further vet the plant to make sure it isn’t toxic in other ways. “I think there is a real possibility for its use as a foodstuff in the future, provided there is extensive research on possible toxin content due to their symbiotic cyanobacteria,” says Winstead. “Corn is currently used as biofuel, livestock feed, and a foodstuff, and I think azolla holds a similar potential.”
Azolla's relentless growth may come in particularly handy in case of a disaster, when traditional food infrastructure falls to pieces. That cultivation might happen outdoors—in engineered ponds—or in indoor farms. “It only needs 2 inches of water to grow,” says Winstead. “So you could have a whole bunch of 2-inch trays stacked on top of each other with grow lights. And you could be getting a massive amount of biomass coming out of that really small space.”
Like legumes, azolla has the enviable superpower of being able to fix its own nitrogen, meaning you don’t have to soak it in synthetic fertilizers for it to proliferate. It’s those potentially toxic symbiotic cyanobacteria, also known as blue-green algae, within the plants that do the actual fixing. “Azolla fixes an amazing amount of nitrogen,” says Jagdish Ladha, a soil scientist and agronomist at the University of California, Davis, who wasn’t involved in the new research. “If you provide phosphorus and you have water and if you have sunshine, it multiplies like hell.”
Azolla was actually a hot research topic in Asia in the 1980s, Ladha says. Because of a fertilizer shortage, rice producers were looking for other ways to provide crops with nitrogen. Azolla is a perfect match for rice production, since it can proliferate across flooded paddies. Not only does azolla provide lots of free nitrogen, but the plant cover helps suppress weeds and reduces the emission of methane, a far more potent greenhouse gas than CO2.
However, to actually utilize that nitrogen, the azolla biomass has to be “incorporated” into the soil—mixed in by machine. “In short, it was a very, very labor-intensive technology,” says Ladha. And while azolla produces its own nitrogen, it needs applications of phosphorus to properly grow, which adds to the costs. Accordingly, research interest in azolla dropped off after the 1980s. But Ladha reckons that Winstead’s new paper could fuel renewed interest. Scientists might find a way, for instance, to sustainably cultivate azolla and turn it into fertilizer for other crops beyond rice.
As it grows and photosynthesizes, azolla takes in carbon dioxide from the atmosphere and spits out oxygen. The aquatic fern is so good at capturing carbon, in fact, that it has a global phenomenon named after it: the Azolla Event. Some 49 million years ago—the theory goes—azolla bloomed in such quantities in the Arctic that it helped crash global atmospheric CO2 levels, which then dramatically cooled the world.
So if we cultivate more azolla, we capture more carbon (though of course not on the same scale as 49 million years ago). If azolla is added to fields as fertilizer, some of that carbon is sequestered in the ground. And if scientists can figure out how to turn it into a biofuel—much like they’ve done with corn—then it can help reduce net carbon emissions. Instead of adding extra CO2 to the air, as happens when burning fossil fuels, burning an azolla-based fuel would release carbon that the plant had drawn down from the atmosphere when it grew.
“It would definitely be a much more sustainable form of combustible fuel, for sure, especially if you use sunlight [to grow it],” says Winstead. “If you start using artificial lights and stuff, you’ve got to worry about where that energy is coming from.” That is, you wouldn’t want to power your facility with fossil fuels, since you’d produce carbon emissions to make your supposedly climate-friendly fuel.
In the economically developing world, all these charms of azolla combine into a sort of super-solution. It’s been used for thousands of years to feed cows and chickens, and still is, says David Hughes, founder of PlantVillage, which is using technology to help farmers in Africa adapt to climate change. “A happy cow is one who is sitting down and eating as much as they can,” says Hughes. “So if you can grow azolla on a localized basis and feed it to the animals, then you’ve got a much more controlled system. Definitely 10 out of 10—it’s a great product.”
Growing azolla can help with water security as well, as a mat of vegetation on the surface of a water tank reduces evaporation. “You could have a wall around your farm, which are all these tanks of azolla growing,” says Hughes. “So you’re capturing carbon and you’re feeding your animals, but in the moments you actually need water, you could just open the spigot, and then irrigate your fields.”
Long the obsession of ducks, azolla could grow into an increasingly essential crop for humans, too. “It's just an amazing plant,” says Ladha. “The fact that we stopped researching 1990s and 2000s, doesn't mean that it should not be explored again.”
