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Sunflower

Sunflower
Sunflowers display bright yellow colors.
Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Asterales
Family: Asteraceae
Genus: Helianthus
Species: annuus
Binomial name
Helianthus annuus L.

The sunflower (Helianthus annuus) is an annual plant in the Family Asteraceae with a large flower head. The stem of the flower can grow up to 17ft tall, with the flower head reaching 30cm in diameter. The sunflower is notable for turning to face the sun, a behavior known as heliotropism.

History
One of the few cultivated plants native to North America, it is believed that wild sunflowers once covered thousands of square miles of land that is now the western United States. Sunflower remains have been found in North American archaeological sites dating from as early as 3,000 B.C. The center of origin for wild sunflowers is considered to be the Western Plains of North America, but the ancestors of the cultivated type have been traced to the Southwest or the Missouri-Mississippi River valley areas. The first breeders of sunflowers appear to be the Ozark Bluff dwellers who selected plants and seed for cultivation.

Francisco Pizarro found the Inca subjects 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".

Description
The term "sunflower" is also used to refer to all plants of the genus Helianthus, many of which are perennial plants.

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 disc florets mature into "seeds". However, what we commonly call the seeds are actually the fruit of the plant, with the true seeds encased in an inedible husk.

Mathematical Properties
Sunflower heads contain seeds in spiral patterns. There will be one family of spirals that goes clockwise and another family of spirals that interlaces between these, going counter-clockwise. Counting the number of spirals in each family will reveal each to be a Fibonacci number, typically 34 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.

Marble bust of 'Clytie'Greek myth
In Greek mythology, a water-nymph named Clytie fell in love with the sun god Apollo, and would do nothing but watch his chariot move across the sky. Spurned by Apollo, who loved another, Clytie tasted neither food nor drink and after nine days, her limbs rooted into the ground, and her face became a sunflower, which turns on its stem so as to always face the sun.  A marble bust of Clytie (Roman circa 40-50AD) can be found in the British Museum.

Heliotropism
Most flowerheads on a field of blooming sunflowers are turned towards the east, where the sun rises each morning. Immature sunflowers in the bud stage exhibit heliotropism; on sunny days the bud tracks the sun on its journey along the sky from east to west, while at night or at dawn it returns to its eastward orientation. The motion is performed by motor cells in the pulvinus, a flexible segment of the stem just below the bud. The stem stiffens at the end of the bud stage, and when the blooming stage is reached the stem freezes in its eastward direction. Thus, blooming sunflowers are not heliotropic anymore, even though most flowerheads are facing the direction where the sun rises.

Cultivation and Uses
To grow well, sunflowers need full sun. They grow best in fertile, moist, well-drained soil with a lot of mulch. Seeds should be 45 cm (1.5') apart and planted 2.5 cm (1") deep.

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), as a carrier oil and is used to produce biodiesel, for which it is less expensive than the olive product. The cake remaining after the seeds have been processed for oil is used as a livestock feed. Some recently developed cultivars have drooping heads. These cultivars are less attractive to gardeners growing the flowers as ornamental plants, but appeal to farmers, because they reduce bird damage and losses from some plant diseases. There are also new breeds of sunflowers which are transgenic, so that they are resistant to some diseases. Sunflowers also produce latex and are the subject of experiments to improve their suitability as an alternative crop for producing hypoallergenic rubber.

The sunflower is the state flower of the U.S. state of Kansas, and one of the city flowers of Kitakyushu, Japan.

Amazing Facts
Scientific literature reports, from 1567, that a 12 m (40'), traditional, single-head, sunflower plant was grown in Padua, Italy. The same seed lot grew almost 8 m (24') at other times and places. In recent years, sunflowers over 8 m (25') have been grown in both Netherlands and Canada.

Source: Wikipedia