For the first time, we welcome sunflowers in our garden below.
I took several photos of how they grow and began to study their behaviour, interesting life and uses from Wikipedia.The
sunflower (Helianthus annuus) is an annual plant in the family Asteraceae and native to the Americas, with a large flowering head (inflorescence).

What is usually called the "
flower" is actually a "
head" (formally composite flower) of numerous florets (small flowers) crowded together. The
outer florets are the sterile
ray florets and can be yellow, maroon, orange, or other colors. The
florets inside the circular head are called
disc florets, which mature into what are traditionally called "
sunflower seeds," but are actually the
fruit (an achene) of the plant. The
inedible husk is the
wall of the
fruit and the
true seed lies within the
kernel.
The
florets within the sunflower's cluster are arranged in a
spiraling pattern. Typically each floret is oriented toward the next by approximately the
golden angle, 137.5°, 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 one direction and 55 in the other; on a very large sunflower there could be 89 in one direction and 144 in the other.


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 follow 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.
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 ft) apart and 2.5 cm (1 in) deep.
Sunflower "whole seed" (fruit) are sold as a
snack food, after roasting in 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. In Germany, it is mixed together with rye flour to make
Sonnenblumenkernbrot (literally: sunflower whole seed bread), which is quite popular in German-speaking 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
margarine and
biodiesel, as it is cheaper than olive oil. 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.
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.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.
Sunflowers may also be used to
extract toxic ingredients from soil, such as lead, arsenic and uranium. They were used to remove uranium, cesium-137, and strontium-90 from soil after the Chernobyl accident (see phytoremediation).

A
Mathematical model for the pattern of florets in the head of a sunflower was proposed by H Vogel in 1979 for n=1..500 . This is expressed in polar coordinates
r = c (square root of n),
θ = n (137.5 degress),
where θ is the
angle, r is the radius or
distance from the center, and n is the
index number of the floret and c is a
constant scaling factor.
It is a form of
Fermat's spiral. The angle 137.5° is related to the
golden ratio and gives a close packing of florets. This model has been used to produce computer graphics representations of sunflowers.

Note that The sunflower is
[1] the
state flower of Kansas, U.S.A. and one of the
city flowers of Kitakyushu, Japan.
[2] used as a symbol of
green ideology, much as the red rose is a symbol of socialism or social democracy. The sunflower is also the symbol of the
Vegan Society.
[3] the
subject of
Van Gogh's most famous
still life, Sunflowers (series of paintings).