The Azolla fern isn’t much to look at. It has tiny leaves and floats en masse on top of water . Many people consider it a watery weed: it can cover the entire surface of a lake or pond, choking off sunlight to other water plants. No one thinks swimming with Azolla is fun.
But Azolla is a miracle plant. The Scientific American just reported that 55 million years ago (ten million years after the end of the dinosaurs), when carbon dioxide levels were much higher than today and the Earth was much warmer, the Azolla fern came to the rescue. The Arctic Ocean was a big inland lake at the time, hot and overloaded with nitrogen. The evidence is that the fern grew abundantly in the lake, and when the seasonal rains fell, the Azolla spread out over the surrounding continents. As the ferns photosynthesized and grew, they sucked up carbon dioxide from the atmosphere in great quantities. During dry spells, the ferns died and their remains (and their carbon components) settled onto the land and became buried under sediment. This boom and bust cycle went on for a million years, and during that period, atmospheric carbon dioxide levels dropped by roughly half. Author Jennifer Huizen raises the question of whether Azolla might play a role in countering global warming today.
That’s not the only great thing about Azolla. I’ve been digging into algae (sometimes literally) and discovered that rice, Azolla, and algae are linked. Paddy farmers plant Azolla in the water next to rice plants. The ferns have symbiotic blue-green algae that help the ferns absorb nitrogen. The nitrogen is passed along to the rice plants, increasing their productivity significantly.
There are more great things to be said (and I will say them next week) for Azolla. But let me say this: It’s a weed we need!