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Carl Linnaeus first collected samples of these weird spheres in Sweden in 1753. But they weren’t called “marimo” until Takuya Kawakami, another botanist, found them along Lake Akan in Hokkaido, Japan, more than a century later. Now they are a protected national treasure, and every October (this year Oct. 8 to 10), Japan’s Ainu people host a festival in which they first welcome the marimo to Lake Akan, collect them and then return them in a sacred ceremony.

Collecting them from Lake Akan is otherwise prohibited, but some keep marimo, man-made or collected elsewhere, as aquarium pets — which is how they captured the attention of Dora Cano-Ramirez, the lead author of the paper.

After purchasing her own marimo, she noticed that bubbles covered them at some times of day and not others. And during the day, a few moved to the top of her tank. Because she studied how biological clocks control photosynthesis in land plants, she wondered if the same kinds of processes might be at play in her light-harvesting algae balls. She took her idea to Antony Dodd, a biologist and head of her lab.

“The rationale behind the work was a little whimsical,” Dr. Dodd said. “But in science sometimes you get interested in things, and if you have a chance, it’s worth pursuing them just to find out more about the world.”