Sunflowers always turn with the sun because of their heliotropism. 向日葵的向光性使它总是随着太阳的方向而移动。
Heliotropism A form of phototropism in which flowers move to point toward the sun, tracking it as it moves across the sky. 向日性：趋光性的一种类型，植物的花在一天内朝向太阳，并随着日光照射的方向而转移方位。
Recent explanations for heliotropism of sunflower 葵花向阳原因新解析
