The sunflower broad center contains up to 2,000 tiny flowers. They need to maximize their sunlight intake. So, from sunrise to its set, sunflowers follow the sun in the sky. They face east in the morning, and end up facing west by dusk. During the night, they slowly turn back, to be facing east in the morning.
As Sunflowers mature, they gradually stop following the sun, and remain facing east. One theory for this is, east-facing flowers heat up faster. Bees like warm flowers so these mature, east-facing blooms attract more bees. They make the bees happy, and promote cross pollination among neighboring blooms.
Now that’s a romantic flower!