Plant · P-888

Mosquito Fern

Azolla filiculoides

Water Fern is a tiny free-floating fern that carries its own built-in nitrogen fixer, a cyanobacterium living in a pocket inside every leaf, so it needs no soil partner to make nitrogen-rich biomass. The mat can double in as little as three days, and farmers in southern China and northern Vietnam have grown it as a living fertilizer ahead of rice for centuries. Dried or fresh, it also makes a high-protein feed for poultry, pigs, ducks and some fish, though the safe share of the ration varies by animal. The catch is that it soaks up heavy metals and other pollutants from the water it grows in just as readily as nutrients, so a pond used to clean dirty water should never supply feed - that has to come from a separate, clean pond.