Scientists have long noticed how sunflowers turn toward the east as the sun rises, continuing to follow the sun as it journeys across the sky throughout the day. However, exactly why sunflower behave in this way hasn’t been known, until now.
Scientists found that following the sun attributed to the growth and general thriving of the plant. However, once sunflowers have reached maturity, they always face east and stop tracking the sun. According to a press release about the study:
“As overall growth slows down, the circadian clock ensures that the plant reacts more strongly to light early in the morning than in the afternoon or evening, so it gradually stops moving westward during the day.” 
Researchers came to their conclusion by tying up sunflowers so they were unable to move, or facing them away from the sun. Eventually, they found that those sunflowers had less biomass and a smaller leave area than those that were allowed to move freely. It was also found that bees prefer warm plants, so those who faced the sun were able to attract more pollinators.
The scientists also used artificial light at random intervals to see if the sunflowers could track the light. It was found that they were able to do so on a 24-hour clock, but not when an artificial day reached 30 hours.
Stacey Harmer, a biologist at UC Davis who was involved in the study, stated:
“At nighttime, you could see the whole plant rearranging itself, and it was such an amazing thing. I tell my students all the time that plants are capable of incredible things – we just don’t notice because their time scale is different than ours.” 
Anne Sylvester, the director of the National Science Foundation’s Plant Genome Research Program, which funded the study, said in a press release.
“Just like people, plants rely on the daily rhythms of day and night to function. Sunflowers, like solar panel arrays, follow the sun from east to west. These researchers tap into information in the sunflower genome to understand how and why sunflowers track the sun.”
However much we don’t know about sunflowers, it is still evident that they follow a rhythm. Scientists will be able to use this study to further their research on a wide variety of plants and animals.