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Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Asterales
Family: Asteraceae
Genus: Helianthus
Species: annuus
Binomial name
Helianthus annuus

The sunflower (Helianthus annuus) is a large (to 3 m) annual plant in the Family Asteraceae with a flower head (inflorescence) as much as 30 cm (1 ft) across and notable for turning to face into the sun. Sunflowers are native to the Americas, and were domesticated around 1000 B.C. Francisco Pizarro found the Incas venerating the sunflower as an image of their sun god, and gold images of the "flower" as well as seeds were taken back to Europe early in the 16th century. Helianthus is from the Greek for "sunflower".

What is called the flower is actually a head (formerly composite flower) 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 such that each is separated from the next by approximately the golden ratio, producing a pattern of spirals where the number of left spirals and the number of right spirals are successive Fibonacci numbers. The disc florets mature into "seeds". However, what we commonly call the seeds are actually the fruit (an achene) of the plant, with the true seeds encased in an inedible husk. Sunflower "whole seeds" (fruit) are sold as snacks, especially in the United States and Europe, and as food for birds.

Sunflower oil, extracted from the seeds, is used for cooking (but is less cardiohealthy than olive oil) and is used to produce biodiesel, for which it is less expensive than the olive product. The meal remaining after the seeds have been processed for oil is used as a livestock feed. Some recently developed varieties have drooping heads. These varieties are less attractive to gardeners growing the flowers as ornamentals, but appeal to farmers, because they reduce bird damage and losses from some plant diseases.

The sunflower is the state flower of the U.S. state of Kansas.

The Jerusalem artichoke (Helianthus tuberosa) is related to the sunflower. The Mexican sunflower is Tithonia rotundifolia. False sunflower refers to plants of the genus Heliopsis.