Everything about The Sunflower totally explained
The
sunflower (
Helianthus annuus) is an
annual plant native to the Americas in the family
Asteraceae, with a large flowering head (
inflorescence). The stem of the flower can grow as high as 3 metres tall, with the flower head reaching up to 30 cm in diameter with the "large" seeds. The term "sunflower" is also used to refer to all plants of the
genus Helianthus, many of which are
perennial plants.
Description
What is usually called the
flower is actually a
head (formally
composite flower) of numerous flowers (
florets) crowded together. The outer flowers are the
pubic florets and can be
yellow,
maroon,
orange, or other
colors, and are sterile. The florets inside the circular head are called
disc florets. 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.
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.
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 doesn't turn toward the sun; its flowering heads may face many directions when mature. However, the leaves typically exhibit some heliotropism.
Cultivation and uses
The sunflower is native to the
Americas. Current research shows that it may have been domesticated twice, first in
Mexico and later in the middle
Mississippi Valley. Alternatively, it may have been introduced northward from Mexico at an early date as corn (
maize) had been. The evidence thus far is that the sunflower was first domesticated in Mexico by at least 2600 BC. The earliest known examples of a fully domesticated sunflower north of Mexico have been found in Tennessee and date back to around 2300 B.C. Many indigenous American peoples used the sunflower as the symbol of the sun deity, including the
Aztecs and the
Otomi of Mexico and the
Incas in
South America.
Gold images of the flower, as well as
seeds, were taken back to
Spain early in the 16th century.
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 and 2.5 cm (1") deep.
Sunflower "whole seed" (fruit) are sold as a snack food after roasting within heated ovens with or without salt added. Sunflowers can be processed into a
peanut butter alternative,
Sunbutter, especially in
China,
Russia, the
United States, the
Middle East and
Europe.
It is also sold as food for
birds and can be used directly in cooking and
salads.
Sunflower oil, extracted from the
seeds, is
used for cooking, as a
carrier oil and to produce
biodiesel, for which it's less expensive than the
olive product. A range of sunflower varieties exist with differing fatty acid compositions; some 'high oleic' types contain a higher level of healthy monounsaturated fats in their oil than even
olive oil.
During the 18th Century, the use of sunflower oil became very popular in Europe, particularly with members of the Russian Orthodox Church because sunflower oil was one of the few oils that wasn't prohibited during Lent.
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. Sunflowers also produce
latex and are the subject of experiments to improve their suitability as an alternative crop for producing
hypoallergenic rubber.
Traditionally, many Native American groups included the sunflower as the "fourth sister" with the better known "three sisters" combination of corn, beans, and squash (Kuepper & Dodson, 2001 ). Annual species are often planted for their
allelopathic properties.
However, for commercial farmers growing commodity crops, the sunflower, like any other unwanted plant, is often considered a
weed. Especially in the midwestern USA, wild (perennial) species are often found in corn and soybean fields and can have a negative impact on yields.
Mathematical model
A model for the pattern of
florets in the head of a sunflower was proposed by H Vogel. This is expressed in
polar coordinates »
