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.
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
