A field of sunflowers in Yolo County, California. (Photo by Chris Nicolini, UC Davis)
Sunflowers not only pivot to face the sun as it moves across the sky during the day, but they also rotate 180 degrees during the night to greet the morning sun.
UC Davis and UC Berkeley researchers have now discovered how they do it: They’ve linked their internal clock genes to stem growth, so that the eastern side of the stem elongates more than the western side during the day, turning the stem and flower westward to track the transiting sun.
At night, the western side grows faster, turning the flower head back east in time to capture the rays of the rising sun.
What’s more, once the plant has grown to maturity, the clock genes turn off this differential growth, leaving the flower facing east to gather the heat of the morning sun and provide a warm platform for pollinating bees.