There are about fifty species of sunflowers. Sunflower is a plant native to North America. Flowering lasts three months in summer. Sunflower is a clock regulated plant. It is governed by phototropism, that is, its growth depends on its orientation to light. Only young plants follow the movement of the sun, hour after hour, day after day. Once the flower has formed, the sunflower freezes towards the rising sun. Photo credit: Aaron Burden