Sunflower (Helianthus annuus) is an annual plant native to the Americas. It possesses a large inflorescence (flowering head). The sunflower is named after its huge, fiery blooms, whose shape and image is often used to depict the sun. It has a rough, hairy stem, broad, coarsely toothed, rough leaves and circular heads of flowers.
The heads consist of many individual flowers which mature into seeds, often in the hundreds, on a receptacle base. From the Americas, sunflower seeds were brought to Europe in the 16th century, where, along with sunflower oil, they became a widespread cooking ingredient. Leaves of the sunflower can be used as cattle feed, while the stems contain a fibre which may be used in paper production.
What is usually called the "flower" on a mature sunflower is actually a "flower head" (also known as a "composite flower") of numerous florets (small flowers) crowded together. The outer petal-bearing florets are the sterile florets and can be yellow, red, orange, or other colors. The florets inside the circular head are called disc florets, which mature into seeds.
The flower petals within the sunflower's cluster are usually in a a spiral pattern. Generally, each floret is oriented toward the next by approximately the golden angle, 137.5°, producing a pattern of interconnecting 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 there could be 89 in one direction and 144 in the other. This pattern produces the most efficient packing of seeds within the flower head