called the
flower is actually a
head (formally composite flower) of numerous flowers (florets) crowded together. The outer flowers are the ray florets and can be
yellow,
maroon,
orange, or other
colors, and are sterile. The florets inside the circular head are called disc florets.
Sunflower head displaying florets in spirals of 34 and 55 around the outside
The florets within this cluster are arranged spirally. Typically each floret is oriented toward the next by approximately the
golden angle, 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 1 direction and 55 in the other; on a very large sunflower you may see 89 in one direction and 144 in the other.
The disc florets mature into what are traditionally called "
sunflower seeds", but are actually the
fruit (an
achene) of the plant. The true seeds are encased in an inedible husk.
[
edit] Heliotropism
Sunflowers in the
bud stage exhibit
heliotropism. At sunrise, the faces of most sunflowers are turned towards the east. Over the course of the day, they move to track the sun from east to west, while at night they return to an eastward orientation. This motion is performed by motor cells in the pulvinus, a flexible segment of the stem just below the bud. As the bud stage ends, the stem stiffens and the blooming stage is reached.
Sunflowers in the blooming stage are not heliotropic anymore. The stem has frozen, typically in an eastward orientation. The stem and leaves lose their green color.
The wild sunflower typically does not turn toward the sun; its flowering heads may face many directions when mature. However, the leaves typically exhibit some heliotropism.
[
edit] Cultivation and uses
A sunflower farm near
Mysore, India.
Sunflower heads solds as
snacks in China.
Sunflowers are native to the
Americas. The earliest known examples of a fully domesticated sunflower were found at the
Olmec site of
San Andrés dating some time before 2500 B.C.
[1] The
Incas used the sunflower as an image of their
sun god.
Gold images of the flower, as well as
seeds, were taken back to
Europe early in the
16th century.
The Giant sunflower (Hlianthus giganteus) is native to Connecticut. They can grow to be between 3 and 12 feet tall. Their flower heads can be between 2 to 3 inches wide. They are most commonly found in valleys with wet meadows or swamps. The Giant sunflower grows between July and October.
To grow well, sunflowers need full sun. They grow best in fertile, moist, well-
drained soil with a lot of
mulch. In commercial planting, seeds are planted 45 cm (1.5') apart
