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 ''ray 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.
Sunflower head displaying florets in spirals of 34 and 55 around the outside
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.
Cultivation and uses
A sunflower farm near
Mysore, India.
Sunflower heads sold as
snacks in China.
Sunflowers are native to the
Americas. There is some debate about where the sunflower was first domesticated. The earliest known examples of a fully domesticated sunflower were found at the
Hayes site in Tennessee and date back to around 2300 B.C. There were also other remains found at the
Olmec site of
San Andrés dating some time before 2100 B.C. 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.
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 is 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 was not 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.
For farmers growing other crops, the sunflower is considered a
weed. The wild variety will grow unwanted in corn and soybean fields which 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
:
,
:
,
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.
[1]
Size
Sunflowers most commonly grow to heights between 2.5 and 3.5
m (8 - 12
'). Scientific literature reports, from
1567, that a 12 m (40'), traditional, single-head, sunflower plant was grown in
Padua. The same seed lot grew almost 8 m (24') at other times and places (e.g.
Madrid). Much more recent feats (past score years) of over 8 m (25') have been achieved in both
Netherlands and
Ontario,
Canada.
Cultural usage
★ The sunflower is the state flower of the U.S. state of
Kansas, and one of the city flowers of
Kitakyushu,
Japan.
★ The sunflower is often 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.
Other species
★ The
Jerusalem artichoke (''Helianthus tuberosa'') is related to the sunflower.
★ The 'Mexican sunflower' is ''Tithonia rotundifolia''.
★ 'False sunflower' refers to plants of the genus ''Heliopsis''.
Flower formation
Gallery
See also
★
★
Red sunflower
Notes
1. The Algorithmic Beauty of Plants, , Przemyslaw, Prusinkiewicz, Springer-Verlag, , ISBN 978-0387972978
References
★ Pope, Kevin; Pohl, Mary E. D.; Jones, John G.; Lentz, 3 David L.; von Nagy, Christopher; Vega, Francisco J.; Quitmyer Irvy R.; "
Origin and Environmental Setting of Ancient Agriculture in the Lowlands of Mesoamerica", ''
Science'', 18 May 2001:Vol. 292. no. 5520, pp. 1370 - 1373.
★ Shosteck, Robt. 1974. ''Flowers and Plants. An International Lexicon with Biographical Notes''. Quadrangle/The New York Times Book Co. 329 pp.
★ Wood, Marcia. June 2002. "Sunflower Rubber?" Agricultural Research. USDA.
[1]
External links
★
National Sunflower Association
★
A farmer running his tractor and car with sunflower oil
★
William Blake's poem, "Ah! The sunflower."
★
Allen Ginsberg's poem, "Sunflower Sutra."
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