the.com/heliotropism

means The tendency of plant parts — especially flowers and leaves — to turn or grow in response to the direction of sunlight.

from Built from Greek 'helios' (sun) and 'tropē' (a turning), the same '-tropē' that gives us 'trophy' (originally a turning-point marker in battle) and shows up in words like 'phototropism.' The sunflower lent the phenomenon its popular face, though botanists note true heliotropism is a slower growth response, not the flower swiveling in real time like a tiny solar dish.