Scientific classification
Kingdom: Plantae
Phylum: Magnoliophyta
Class: Magnoliopsida
Order: Asterales
Family: Asteraceae
Genus: Helianthus
Species: H. annuus
Binomial name
Helianthus annuus
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.
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.
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.[1] 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. Some researchers argue that the Spaniards tried to suppress cultivation of the sunflower because of its association with solar religion and warfare.[2]
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. In Germany, it is used 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 as well as and 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.
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 [[1]]). 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
Illustration of Vogel's model for n=1..500 .
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 ? 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. [3]
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.
Subject of Van Gogh's most famous still life, Sunflowers (series of paintings)
Varieties
American Giant Hybrid
Arikara
Autumn Beauty
Aztec Sun
Black Oil
Dwarf Sunspot
Evening Sun
Giant Primrose
Indian Blanket Hybrid
Irish Eyes
Italian White
Kong Hybrid
Large Grey Stripe
Lemon Queen
Mammoth Sunflower
Mongolian Giant
Orange Sun
Red Sun
Ring of Fire
Rostov
Soraya
Sunny Hybrid
Taiyo
Tarahumara
Teady Bear
Titan
Valentine
Velvet Queen
Other species
The Maximillian sunflower (Helianthus maximillianii) is one of 38 species of perennial sunflower native to North America. The Land Institute and other breeding programs are currently exploring the potential for these as a perennial seed crop
The Jerusalem artichoke (Helianthus tuberosa) is related to the sunflower, another example of perennial sunflower.
The Mexican sunflower is Tithonia rotundifolia. It is only very distantly related to North American sunflowers.
False sunflower refers to plants of the genus Heliopsis.
Meanings of Sunflowers
No flower can lift spirits quite like sunflowers can. Bright and cheery, bold yet comfortable, the sunflower is a warm and caring gift. With brilliant yellow petals that surround the flower's center, sunflowers have an unmistakable sun-like appearance that has made them a passionate flower choice for many. Sunflowers come in a number of varieties, ranging from small to large and from daylight yellows to sunset reds.
Sunflowers originated in the Americas in 1000B.C., where for centuries they were cultivated as a valuable food source. The use of sunflower images as religious symbols has also been documented in some native societies. With the European exploration of the New World, the sunflower was brought to new areas, and the flower's popularity eventually spread as the rest of the world began to appreciate its beauty and sustenance. Artists throughout history have appreciated the sunflower’s unique splendor, and those of the Impressionist era were especially fixated on the flower. Today, sunflowers continue to provide a resource for commonly used seeds and oil, but they have also become recognized as a floral symbol of great significance.
Much of the meaning of sunflowers stems from its namesake, the sun itself. Wild sunflowers are often photographed with their tall stalks and bright petals stretched towards the sun. This unique behavior, known as phototropism, is a motif that has appeared in many ancient myths and is viewed as a symbol of loyalty and constancy. Their physical resemblance to the sun has also influenced their meanings. The sunflower’s petals have been likened to bright yellow rays of sunshine, which evoke feelings of warmth and happiness. In addition, the sunflower is often associated with adoration and longevity.
For a flower which reflects so many of the sun's positive characteristics, it is little surprise that people enjoy basking in the sunflower’s warming glow. With the sense of brightness and warmth that sunflowers naturally impart, they have become an ideal choice for sending sentiments of cheerfulness and sunny thoughts.
http://www.proflowers.com/flowerguide/f ... gglgeneric
http://en.wikipedia.org/wiki/Sunflower
