Sunflower

The sunflower is an annual plant in the family Asteraceae, with a large flower head.The stem of the flower can grow up to 3 metres tall, with the flower head reaching 30cm in diameter. The term "sunflower" is also used to refer to all plants of the genus Helianthus, many of which are perennial plants.What is usually called the flower is actually a head of numerous flowers crowded together. The outer flowers are the ray florets and can be yellow, maroon, orange, or other colors. These flowers are sterile. The flowers that fill the circular head inside the ray flowers are called disc florets.

The arrangement of florets within this cluster is typically such that each is separated from the next by approximately the golden angle, producing a pattern of spirals where the number of left spirals and the number of right spirals are successive Fibonacci numbers. Typically, there are 34 spirals in one direction and 55 in the other; on a very large sunflower you may see 89 in one direction and 144 in the other.