Plants like to align themselves with the sun – more light means more photosynthesis. When sunflowers grow up, they do the same. During the day, they move with the sun. So in the morning, they face east, where the sun rises. Throughout the day, they follow it across the south to the west in the evening. There the sun sets, the sunflower turns back to the east during the night, and the game starts the next day again.
With “adult” sunflowers, i.e., when they have fully blossomed, things are different: they remain fixed with their gaze in the east – always and all day long. Researchers at the University of California have investigated why they do this in various experiments by comparing sunflowers oriented to the east with those turned to the west.
It came out that the sunflowers turned to the east to attract more bees in the morning. The morning warmth makes the nicely warmed flowers more attractive to the insects. Invisible to us, ultraviolet markings on the petals light up for the pollinators due to the sunlight. This saves them energy in their search for food.
In addition, the stamens release pollen earlier in the morning, which in turn is beneficial for pollinators that are active at the same time. According to the researchers’ experiments, this is due to the temperature at the flower head, which controls this effect. For the same results, they could observe when they artificially warmed sunflowers twisted to the west with a heater.
But also for the sunflower itself, the morning warmth has more advantages: Experiments have shown that plants turned to the east produced more pollen than those turned to the west. And tilted to the east, they grow larger and heavier seeds – a success for reproduction. “Facing the morning sun makes for more offspring,” explains Stacey Harmer.
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