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Helianthus annuus | |
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Scientific classification | |
Kingdom: | Plantae |
(unranked): | Angiosperms |
(unranked): | Eudicots |
(unranked): | Asterids |
Order: | Asterales |
Family: | Asteraceae |
Subfamily: | Helianthoideae |
Tribe: | Heliantheae |
Genus: | Helianthus |
Species: | H. annuus |
Binomial name | |
Helianthus annuus L. |
Sunflower (Helianthus annuus) is an annual plant native to the Americas. It possesses a large inflorescence (flowering head). The sunflower is named after its huge, fiery blooms, whose shape and image are often used to depict the sun. It has a rough, hairy stem, broad, coarsely toothed, rough leaves and circular heads of flowers. The heads consist of many individual flowers which mature into seeds, often in the hundreds, on a receptacle base. From the Americas, sunflower seeds were brought to Europe in the 16th century, where, along with sunflower oil, they became a widespread cooking ingredient. Leaves of the sunflower can be used as cattle feed, while the stems contain a fibre which may be used in paper production.
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What is usually called the "flower" on a mature sunflower is actually a "flower head" (also known as a "composite flower") of numerous florets (small flowers) crowded together. The outer petal-bearing florets are the sterile florets and can be yellow, red, orange, or other colors. The florets inside the circular head are called disc florets, which mature into seeds.
The flower petals within the sunflower's cluster are always in a a spiral pattern. Generally, 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.[1][2][3] This pattern produces the most efficient packing of seeds within the flower head.[4][5][6]
Sunflowers commonly grow to heights between 1.5 and 3.5 m (5–12 ft). The tallest sunflower confirmed by Guinness World Records is 8.0 m (2009, Germany). In 16th century Europe the record was already 7.3 m (24 ft, Spain).[7] Most cultivars are variants of H. annuus, but four other species (all perennials) are also domesticated. This includes H. tuberosus, the Jerusalem Artichoke, which produces edible tubers.
A common misconception is that sunflower heads track the Sun across the sky.[8] This old and chronic misconception was debunked already in 1597 by the English botanist John Gerard, who grew sunflowers in his famous herbal garden: "[some] have reported it to turn with the Sun, the which I could never observe, although I have endeavored to find out the truth of it."[7] The uniform alignment of sunflower heads in a field might give some people the false impression that they are tracking the sun, but the heads are actually pointing in a fixed direction (East) all day long. However, the uniform alignment does result from heliotropism in an earlier development stage, the bud stage, before the appearance of flower heads (anthesis).[9] The buds are heliotropic until the end of the bud stage, and finally face East. Their heliotropic motion is a circadian rhythm, synchronized by the sun, which continues if the sun disappears on cloudy days. If a sunflower plant in the bud stage is rotated 180°, the bud will be turning away from the sun for a few days, as resynchronization by the sun takes time.[10] The heliotropic motion of the bud is performed by the pulvinus, a flexible segment just below the bud, due to reversible changes in turgor pressure (no growth).
The evidence thus far is that the sunflower was first domesticated in what is now the southeastern US, roughly 5000 years ago.,[11] and possibly introduced into Mexico at an early date, as other crops such as maize were exchanged. The earliest known examples of a fully domesticated sunflower have been found in Tennessee, and date to around 2300 BC[citation needed]. Many indigenous American peoples used the sunflower as the symbol of their solar deity, including the Aztecs and the Otomi of Mexico and the Incas in South America. In 1510 early Spanish explorers encountered the sunflower in the Americas and carried its seeds back to Europe.[12] Of the four plants known to have been domesticated in what is now the continental United States [13] to have become an important agricultural commodity, sunflower is currently the most economically important.
During the 18th century, the use of sunflower oil became very popular in Russia, particularly with members of the Russian Orthodox Church, because sunflower oil was one of the few oils that was allowed during Lent, according to some fasting traditions.
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Raw sunflower seeds, intended for planting. |
To grow best, sunflowers need full sun. They grow best in fertile, moist, well-drained soil with heavy 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, raw or after roasting in ovens, with or without salt and/or seasonings added. Sunflowers can be processed into a peanut butter alternative, sunflower butter. In Germany, it is mixed 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. American Indians had multiple uses for sunflowers in the past, such as in bread, medical ointments, dyes and body paints.[citation needed]
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 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.
Traditionally, several Native American groups planted sunflowers on the north edges of their gardens as a "fourth sister" to the better known three sisters combination of corn, beans, and squash.[14] Annual species are often planted for their allelopathic properties.[15] Results showed that higher water uptake and hull rate was obtained from large seeds. Small seeds germinated and grew more rapidly compared to large seeds of the same cultivars under NaCl stress. NaCl caused lower root and shoot length but higher mean germination time and dry matter. Therefore, viability after accelerated ageing was lower in small seeds than large seeds. Emergence percentage did not change by seed size, but cotyledon length was shorter in small seeds. It was concluded that although large seeds produced vigorous germination and seedling growth yet small seeds could also be used for successful sunflower production in salt affected areas.
However, for commercial farmers growing commodity crops, the sunflower, like any other unwanted plant, is often considered a weed. Especially in the midwestern US, wild (perennial) species are often found in corn and soybean fields and can have a negative impact on yields.
Sunflowers can be used in phytoremediation to extract toxic ingredients from soil, such as lead, arsenic and uranium. They were used to remove caesium-137 and strontium-90 from a nearby pond after the Chernobyl disaster,[16] and a similar campaign was mounted in response to the Fukushima Daiichi nuclear disaster.[17][18]
The sunflower, Helianthus annuus, genome is diploid with a base chromosome number of 17 and an estimated genome size of 2871–3189 Mbp.[19][20] Some sources claim its true size is around 3.5 billion base pairs (slightly larger than the human genome).[21]
A model for the pattern of florets in the head of a sunflower was proposed by H. Vogel in 1979.[22] 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 (55/144 of a circular angle, where 55 and 144 are Fibonacci numbers) and gives a close packing of florets. This model has been used to produce computer graphics representations of sunflowers.[23]
The following are cultivars of sunflowers (those marked agm have gained the Royal Horticultural Society's Award of Garden Merit):-
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There are many species in the sunflower genus Helianthus, and many species in other genera that may be called sunflowers.
Look up sheller in Wiktionary, the free dictionary. |
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External identifiers for Helianthus annuus | |
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Encyclopedia of Life | 468106 |
ITIS | 36616 |
NCBI | 4232 |
Also found in: Wikispecies |
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リンク元 | 「Helianthus」「ヒマワリ」「Helianthus annuus」 |
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