Helianthus - Sunflower

The Helianthus genus comprises 67 species and several subspecies in the Asteraceae family, all of which are native to North America, with some species (particularly Helianthus annuus (sunflower) and Helianthus tuberosus (Jerusalem artichoke)) cultivated in Europe and other parts of the world as food crops and ornamental plants.

These are usually tall, annual or perennial plants, growing to a height of 50-390 cm. The rough and hairy stem is branched in the upper part. The petiolate leaves are dentate and often sticky. The lower leaves are opposite, ovate or often heart-shaped. The upper leaves are alternate and narrower.

They bear several to many wide, terminal capitula (flower heads), with bright yellow ray florets at the outside and maroon disc florets inside. These flower heads follow the direction of the sun, going from east to west during the day.


Sunflower
The sunflower (Helianthus annuus) is an annual plant native to the Americas in the family Asteraceae, with a large flowering head. 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.
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.

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: 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. Some researchers argue that the Spaniards tried to suppress cultivation of the sunflower because of its association with solar religion and warfare.

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.

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.


Culture
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)

Sunflower - Helianthus annuus

Prairie Sunflower - Helianthus petiolaris

Willowleaf Sunflower - Helianthus salicifolius

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