The common sunflower (Helianthus annuus) is a large annual forb of the genus Helianthus. It is commonly grown as a crop for its edible oily seeds.
 
Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as bird food, in some industrial applications, and as an ornamental in domestic gardens. Wild H. annuus is a widely branched annual plant with many flower heads.
 
The domestic sunflower, however, often possesses only a single large inflorescence (flower head) atop an unbranched stem.
 
The plant flowers in summer.
What is often called the "flower" of the sunflower is actually a "flower head" (pseudanthium), 7.5–12.5 centimetres (3–5 in) wide, of numerous small individual five-petaled flowers ("florets").
The outer flowers, which resemble petals, are called ray flowers.
Each "petal" consists of a ligule composed of fused petals of an asymmetrical ray flower. They are sexually sterile and may be yellow, red, orange, or other colors.
The spirally arranged flowers in the center of the head are called disk flowers. These mature into fruit (sunflower "seeds").
 
*Wiki