We all love flowers and sunflower is amongst them. Sunflower is native to America and is an annual plant scientifically known as Helianthus annuus. The inflorescence is very large also known as flowering head. It is called as sunflower because of the fiery blooms, shape and size resembles like that of a sun. The plant can be characterized by presence of rough, hairy stem, broad, coarsely toothed leaves and circular heads of flowers. The flowering head consists of 1,000-2,000 individual flowers joined together by a receptacle base. They were brought to Europe in the 16th century where they became an important part of cooking. The leaves are commonly used as cattle feed while the stem is a good source of fiber used for paper production.
Many individual florets are crowded together within the flowering head. The outer petals of the florets are called as ray florets. They are sterile and may be yellow, orange, red and of other colours. The florets present on the inner side of the head are called as disc florets and are responsible for the production of seeds. The florets in the head are arranged in a spiral pattern. Typically each floret is oriented towards the other floret with a golden angle of 137.5°. The left spiral and the right spirals are so interconnected that they form successive Fibonacci numbers. Generally there are 34 spirals in one direction and 55 on the other. In a very large sunflower there are 89 spirals in one direction and 144 on the other. This pattern is responsible for the production of compact arrangement of seeds within the head. The plant is known to attain a height between 1.5-3.5 m. Scientific literature reports that a sunflower plant with a single headed flower attained a height of 12 m in 1567 in Padua. During the 20th century plants with a height of 8 m have also been produced in Netherlands, Ontario and Canada.
Young sunflowers show a specific phototropic response known as heliotropism where they orient themselves according to the position of the sun and their orientation often changes from east to west during the day as the sun changes its direction. This movement of the flowering heads often becomes circadian and the older pattern is followed for few days but the orientation of leaves occurs from west to east just opposite to that of the flowering head. The orientation of flowering heads and the leaves continue till the plant continues to grow but as the plant attains maturity these movements stop. The movement continues during the day but during night the plants come back to their original position. They are considered to be native to Central America and were first domesticated in Mexico during the 2600 BC.
Sunflowers require proper sunlight in order to grow well. They thrive well in fertile, moist, well drained soil with a lot of mulch. In the commercial practice they are grown at a distance of 45 cm from each other and 2.5 deep. The seeds are sold as whole and are consumed as snack may be salted or roasted. The seeds may be added to the peanut butter in order to produce the sunbutter. Sunflowers are often used by the American-Indians for making ointments and in other medicines. The oil extracted from the seeds is often used for cooking and in the manufacture of margarine and biodiesel. The oil is much cheaper than the olive oil. A large number of sunflower varieties are available differing in the fatty acid composition. Some contain higher levels of monounsaturated fatty acids even more than that of the olive oil. The cakes left after the extraction of oil from the seed is used as cattle feed.
Some recently cultivated species have drooping heads. The flowers with drooping heads are not attractive to the gardeners using sunflowers as ornamental plants but they are quite appealing to the farmers as they remain protected from birds and other plant diseases. They also produce latex that is used in the production of hypoallergenic rubber. Annual species are often grown for their allelopathic properties. In the Midwestern US they are considered as weed as some wild species are found to grow along with the agricultural crops and cast a negative effect over them.
Sunflowers are often used for the extraction of toxic metals from soil like lead, arsenic and uranium. They were also used for the extraction of cesium-137 and strontium-90 during the Chernobyl disaster. The genome has been completely figured out and it is diploid with a base chromosome number of 17 and an estimated genome size of 2871-3189 Mbp. Some scientists claim that the size of genome is about 3.5 million base pairs. It is the state flower of Kansas and one of the city flowers of Japan. It is also a symbol of socialism. It also symbolizes the Vegan Society.