Sunflower buds are not being poetic when they follow the sun; they are running an internal schedule. At the core sits a circadian clock, synchronized to light, that tells one side of the stem to elongate more by day and the opposite side by night, producing that daily swing from east to west and back again.
The striking part is that this tracking is less a reaction to the sun itself than a growth program. Auxin gradients and differential cell elongation in the stem, not muscular motion, drive the movement; even under steady artificial light, the oscillation can persist because the endogenous rhythm keeps firing, much like an internal metronome in chronobiology experiments.
Adult plants, though, abandon this routine because the payoff changes. Once the flower head opens, stem growth slows and heliotropism fades, locking the head toward the east. That fixed posture warms the flower faster each morning through increased radiant heating, making it more attractive to pollinators and boosting seed set, so the plant trades motion for reproductive gain.
