Azolla, Floating Fern

50 million years ago, Azolla grew in such huge quantities near today’s Arctic region that it is credited with removing half of the excess carbon dioxide from the atmosphere. This fast-growing,
high-protein plant is being used for livestock feed, fertilizer, and possibly, for human consumption as well.

https://www.scientificamerican.com/article/can-the-fern-that-cooled-the-planet-do-it-again/
http://www.eriksjodin.net/projects/theazollacookingandcultivationproject/research/Mosquito%20ferns%20-%20tiny%20super%20plants.pdf
http://theazollafoundation.org/