No one knows why sunflowers track the sun, but scientists suspect that it may enhance the flower’s chances for pollination, increase the amount of heat the flower absorbs or accelerate the maturation of the sunflower seeds. Sunflowers achieve their movement through the differential growth rate of the cells in the stem. When the cells on the right side of the plant grow quickly, the flower head tilts the opposite direction.
In addition to their sun-tracking habits, sunflowers are famous for their large flower heads and tall stature. However, the large part at the top of a sunflower head is not a single flower. Called a flower head, this structure contains hundreds or thousands of discrete flowers. After pollination, each flower turns into a seed. The largest sunflower heads may span more than 32 inches in diameter. The tallest sunflower ever recorded grew to more than 25 feet in height.
Sunflower plants grow wild throughout North America, but farmers use cultivated varieties that differ from their wild counterparts in a number of ways. While cultivated varieties produce more seeds per flower head than the wild counterparts do, they only have one head per plant, whereas wild plants may have up to 20 heads on each plant.