Sunflowers Have Better Internal Clocks Than Most People


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For about as long as people have been studying sunflowers, we’ve observed that they gradually pivot their colorful “faces” to follow the movements of the sun over the course of the day. They start each day facing east in order to absorb the maximum amount of sunlight, then by sundown they’ve turned to face toward the west. Then, by the next dawn, they’ve already reset themselves again. Somehow, they seem to have learned where the sun will be at any given time of day.

To figure out all the logistics of how exactly this process works, a team of scientists at University of California, Davis, helmed by Stacey Farmer, decided to conduct some experiments that put the sunflowers’ abilities to the test. First, they would fix the sunflowers in place or face them in the opposite direction, away from the sun, at the start of the day. This disrupted the natural rhythm of the flowers so that further tests could be conducted. The next step was to observe what would happen when the subjects were introduced to an artificial light source that would remain in one spot, unlike the sun. The sunflowers continued their usual swaying pattern for the duration of the test, indicating that their movement is driven by some sort of fixed internal cycle.

The experiment didn’t end there. To reach any concrete conclusions, the scientists would need to simulate a daily cycle with their artificial light source, moving it from east to west over a set period of time. Sure enough, the sunflowers synced up their natural swaying movement to follow the 24-hour cycle. However, when the team tried a 30-hour cycle, the flowers couldn’t keep up. Evidently, their internal clocks are fine-tuned to the natural 24-hour cycle of daylight.

This is not just a random quirk in their genetics; rather, it provides them with several evolutionary benefits. Over countless years, sunflowers have evolved to alternate growth on either side of their stem depending on the time of day, which exposes them to more sunlight and in turn makes them grow much larger and healthier. Bigger, warmer, and more colorful sunflowers also tend to attract more bees looking to pollinate, so their daily swinging pattern is actually a boon to the entire ecosystem.

Proving that sunflowers’ internal clocks are a genetic development opens a lot of doors for future botanical research. Through genetic modification and selective evolution, we could potentially condition any plant of our choosing to adopt similar methods to the sunflower for optimal sunlight exposure, especially since we now know it’s already hardwired to a 24-hour cycle. 

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