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''Helianthus'' () is a genus comprising about 70 species of annual and perennial flowering plants in the daisy family Asteraceae. Except for three South American species, the species of ''Helianthus'' are native to North America and Central America. The common names "sunflower" and "common sunflower" typically refer to the popular annual species ''Helianthus annuus'', whose round flower heads in combination with the ligules look like the sun. This and other species, notably Jerusalem artichoke (''H. tuberosus''), are cultivated in temperate regions and some tropical regions as food crops for humans, cattle, and poultry, and as ornamental plants. The species ''H. annuus'' typically grows during the summer and into early fall, with the peak growth season being mid-summer. Several perennial ''Helianthus'' species are grown in gardens, but have a tendency to spread rapidly and can become aggressive. The whorled sunflower, ''Helianthus verticillatus'', was listed as an endangered species in 2014 when the U.S. Fish and Wildlife Service issued a final rule protecting it under the Endangered Species Act. The primary threats are industrial forestry and pine plantations in Alabama, Georgia, and Tennessee. They grow to and are primarily found in woodlands, adjacent to creeks and moist, prairie-like areas.


Description


thumb|The disk of a sunflower is made up of many little flowers. The ray flowers here are dried


Origin


Sunflowers originate in the Americas. They were first domesticated in what is now Mexico and the Southern United States.''Plant Evolution and the Origin of Crop Species'', By James F. Hancock (CABI, 2012), page 188 Domestic sunflower seeds have been found in Mexico, dating to 2100 BCE. Native American people grew sunflowers as a crop from Mexico to Southern Canada. In the 16th century the first crop breeds were brought from America to Europe by explorers.


History


Sunflowers are thought to be domesticated 3000–5000 years ago by Native Americans who would use them primarily as a source for edible seeds. They were then introduced to Europe in the early 16th century and made their way to Russia. In Russia, where oilseed cultivators were located, these flowers were developed and grown on an industrial scale. Russia then reintroduced this oilseed cultivation process to the North America's in the mid-20th century; North America began their commercial era of sunflower production and breeding. New breeds of the ''Helianthus spp.'' began to become more prominent in new geographical areas. This species' geographical history accounts for its evolutionary history, with its levels of genetic variation across its gene pool increasing as new hybrids are created both for commercial use and in the wild. Subsequent to this, sunflower species are also experiencing the bottle neck effect in their gene pool as a result of selective breeding for industrial use.


Morphology


Sunflowers are usually tall annual or perennial plants that in some species can grow to a height of or more. They bear one or more wide, terminal capitula (flower heads), with bright yellow ray florets at the outside and yellow or maroon (also known as a brown/red) disc florets inside. Several ornamental cultivars of ''H. annuus'' have red-colored ray florets; all of them stem from a single original mutant. During growth, sunflowers tilt during the day to face the sun but stop once they begin blooming. This tracking of the sun in young sunflower heads is called heliotropism. By the time they are mature, sunflowers generally face east. The movement of sunflowers through heliotropism happens as the sunflower follows the sun, the opposite side of the sunflower stem begins to accumulate growth hormones and this causes growth which redirects the sunflower. The rough and hairy stem is branched in the upper part in wild plants, but is usually unbranched in domesticated cultivars. The petiolate leaves are dentate and often sticky. The lower leaves are opposite, ovate, or often heart-shaped. They are distinguished technically by the fact that the ray florets (when present) are sterile, and by the presence on the disk flowers of a pappus that is of two awn-like scales that are caducous (that is, easily detached and falling at maturity). Some species also have additional shorter scales in the pappus, and one species lacks a pappus entirely. Another technical feature that distinguishes the genus more reliably, but requires a microscope to see, is the presence of a prominent, multicellular appendage at the apex of the style. Further, the florets of a sunflower are arranged in a natural spiral. Variability is seen among the perennial species that make up the bulk of those in the genus. Some have most or all of the large leaves in a rosette at the base of the plant and produce a flowering stem that has leaves that are reduced in size. Most of the perennials have disk flowers that are entirely yellow, but a few have disk flowers with reddish lobes. One species, ''H. radula'', lacks ray flowers altogether. ''Helianthus'' species are used as food plants by the larvae of many lepidopterans. The seeds of ''H. annuus'' are used as human food.

Growth stages

The growth of a sunflower depends strictly on its genetic makeup and background. Additionally, the season it is planted will have effects on its development; those seasons tend to be in the middle of summer and beginning of fall. Sunflower development is classified by a series of vegetative stages and reproductive stages that can be determined by identifying the heads or main branch of a single head or branched head.


Production





Fertilizer use


The Journal of Environmental Management has analyzed the impact of various nitrogen-based fertilizers on the growth of sunflowers. Ammonium nitrate was found to produce better nitrogen absorption than urea, which performed better in low-temperature areas.


Production in Brazil


In Brazil, a unique system of production called the soybean-sunflower system is used: sunflowers are planted first, and then soybean crops follow, reducing idle periods and increasing total sunflower production and profitability. Sunflowers are usually planted in the extreme southern or northern regions of the country. Frequently, in the southern regions, sunflowers are grown in the beginning of rainy seasons, and soybeans can then be planted in the summer. Researchers have concluded that the soybean-sunflower method of plantation could be further improved through changes in fertilizer use. The current method has been shown to have positive environmental impacts.


Ecology


Sunflowers have been proven to be excellent plants to attract beneficial insects, including pollinators. ''Helianthus spp.'' are a nectar producing flowering plant that attract pollinators and parasitoids which reduce the pest populations in nearby crop vegetation. Sunflowers attract different beneficial pollinators (e.g., honey bees) and other known insect prey to feed on and control the population of parasitic pests that could be harmful to the crops. Predacious insects are first attracted to Sunflowers once they are planted. Once the ''Helianthus spp.'' reaches six inches and produces flowers it begins to attract more pollinators. Distance between the sunflower rows and crop vegetation plays an important role in this phenomena, hypothesizing that closer proximity to the crops will increase insect attraction. In addition to pollinators of ''Helianthus spp''., there are other factors such as abiotic stress, florivory, and disease which also contribute to the evolution of floral traits. These selective pressures, which stem from several biotic and abiotic factors are associated with habitat environmental conditions which all play a role in the overall morphology of the sunflowers’ floral traits. An ecosystem is composed of both biotic (which are living elements of an ecosystem such as plants, animals, fungi, protists, and bacteria), and abiotic factors (non-living elements of an ecosystem such as air, soil, water, light, salinity and temperature). It is thought that two biotic factors can explain for the evolution of larger sunflowers and why they are present in more drier environments. For one thing, the selection by pollinators is thought to have increased the sunflower’s size in a drier environment. This is because in a drier environment, there are typically less pollinators. As a result, in order for the sunflower to be able to attract more pollinators, they had to increase the morphology of their floral traits in that they had to increase their display size. Another biotic factor that can explain for the evolution of larger sunflowers in drier environments is that the pressure from florivory and disease favours smaller flowers in habitats that have a more moderate supply of moisture (mesic habitat). Wetter environments usually have more dense vegetation, more herbivores, and more surrounding pathogens. As larger flowers are typically more susceptible to disease and florivory, smaller flowers may have evolved in wetter environments which explains the evolution of larger sunflowers in more drier environments.


Phylogeography


Regarding the phylogeographic relations and population demographic patterns across sunflowers, earlier cultivated sunflowers formed a clade from wild populations from the Great Plains, which demonstrates that there was a single domestication event in central North America. Following the cultivated sunflower’s origin, it may have gone through significant bottlenecks dating back to ~5000 years ago.


Medicinal Uses


The seed and sprouts of the common sunflower (''Helianthus annuus L.'') have many medicinal uses. The edible seed and the sprout have an abundance of nutrients and biological activities and have many antioxidants such as phenolic acids, flavonoids and vitamins. The common sunflower has many antioxidant effects which serve as a protective function for cellular damage. Their phytochemical constituents which include phenolic acids, flavonoids and tocopherol, have many potential benefits. The sunflower seed and sprout also have high concentrations of vitamins A, B, and C and are high in niacin. They also have many minerals such as calcium, potassium and iron. Sunflower seed extract contain antidiabetic effects where secondary metabolites within those extracts are able to control glucose levels effectively. The bioactive peptides of the common sunflower are known to have antihypertensive effects. Sunflower oil also helps in anti-inflammatory activity, prevents gastric damages and is a therapeutic alternative in the healing process for microscopical and clinical wounds.


Diversity





Accepted species


There are many species recognized in the genus: * ''Helianthus agrestis'' Pollard – southeastern sunflower – Florida Georgia * ''Helianthus ambiguus'' Britt.Wisconsin Michigan Ohio New York * ''Helianthus angustifolius'' L. – swamp sunflower – Texas + Florida north to southern Illinois + Long Island * ''Helianthus annuus'' L. – common sunflower, ''girasol'' – most of United States + Canada * ''Helianthus anomalus'' S.F.Blake – western sunflower – Nevada Utah Arizona New Mexico * ''Helianthus argophyllus'' Torr. & A.Gray – silverleaf sunflower – Texas North Carolina Florida * ''Helianthus arizonensis'' R.C.Jacks. – Arizona sunflower – Arizona New Mexico * ''Helianthus atrorubens'' L. – purpledisk sunflower – Louisiana Alabama Georgia Florida South Carolina North Carolina Tennessee Kentucky Virginia * ''Helianthus bolanderi'' A.Gray – serpentine sunflower – California Oregon * ''Helianthus × brevifolius'' E.WatsonTexas Indiana Ohio * ''Helianthus californicus'' DC. – California sunflower – California * ''Helianthus carnosus'' Small – lakeside sunflower – Florida * ''Helianthus ciliaris'' DC. – Texas blueweed – Washington California Arizona New Mexico Nevada Utah Texas Oklahoma Colorado Kansas Illinois Tamaulipas Coahuila Chihuahua Sonora * ''Helianthus cinereus'' SmallMissouri Kentucky Indiana Ohio * ''Helianthus coloradensis'' Cockerell – prairie sunflower – Colorado New Mexico * ''Helianthus cusickii'' A.Gray – Cusick's sunflower – Washington Oregon California Idaho Nevada * ''Helianthus debilis'' Nutt. – cucumberleaf Sunflower – Texas to Maine; Mississippi * ''Helianthus decapetalus'' L. – thinleaf sunflower – eastern United States; Ontario Quebec * ''Helianthus deserticola'' Heiser – desert sunflower – Arizona Nevada Utah * †''Helianthus diffusus'' SimsMissouri† * ''Helianthus dissectifolius'' R.C.Jacks. – Mexico * ''Helianthus divaricatus'' L. – woodland sunflower or rough woodland sunflower – eastern United States; Ontario Quebec * ''Helianthus × divariserratus'' R.W.Long Michigan Indiana Ohio Connecticut * ''Helianthus × doronicoides'' Lam.Texas Oklahoma Arkansas Missouri Iowa Minnesota Illinois Kentucky Indiana Ohio Pennsylvania Michigan New Jersey Virginia * ''Helianthus eggertii'' SmallAlabama, Kentucky, and Tennessee * ''Helianthus exilis'' A.GrayCalifornia * ''Helianthus floridanus'' A.Gray ex Chapm. – Florida sunflower – Louisiana Alabama Georgia Florida South Carolina North Carolina * ''Helianthus giganteus'' L. – giant sunflower – eastern United States; most of Canada * ''Helianthus glaucophyllus'' D.M.Sm – whiteleaf sunflower – Tennessee South Carolina North Carolina * ''Helianthus × glaucus'' Small – scattered locales in southeastern United States * ''Helianthus gracilentus'' A.Gray – slender sunflower – California * ''Helianthus grosseserratus'' M.Martens – sawtooth sunflower – Great Plains, Great Lakes, Ontario Quebec * ''Helianthus heterophyllus'' Nutt. – variableleaf sunflower – Coastal Plain Texas to North Carolina * ''Helianthus hirsutus'' Raf. – hairy sunflower – central + Eastern United States, Ontario * ''Helianthus'' × ''intermedius'' R.W.Long – intermediate sunflower – scattered locales in United States * ''Helianthus laciniatus'' A.Gray – alkali sunflower – Arizona New Mexico Texas Coahuila Nuevo León * ''Helianthus'' × ''laetiflorus'' Pers. – cheerful sunflower, mountain sunflower – scattered in eastern + central United States + Canada * ''Helianthus laevigatus'' Torr. & A.Gray – smooth sunflower – Georgia South Carolina North Carolina Virginia Maryland West Virginia * ''Helianthus lenticularis'' Douglas ex Lindl. California Texas * ''Helianthus longifolius'' Pursh – longleaf sunflower – Alabama Georgia North Carolina * ''Helianthus × luxurians'' (E.Watson) E.WatsonGreat Lakes region * ''Helianthus maximiliani'' Schrad. – Maximillian sunflower – much of United States + Canada * ''Helianthus membranifolius'' Poir.French Guiana * ''Helianthus microcephalus'' Torr. & A.Gray – eastern United States * ''Helianthus mollis'' Lam. – downy sunflower, ashy sunflower – Ontario, eastern + central United States * ''Helianthus multiflorus'' L. – manyflower sunflower – Ohio * ''Helianthus navarri'' Phil.Chile * ''Helianthus neglectus'' Heiser – neglected sunflower – New Mexico Texas * ''Helianthus niveus'' (Benth.) Brandegee – showy sunflower – California Arizona; Baja California, Baja California Sur * ''Helianthus nuttallii'' Torr. & A.Gray – western + central United States + Canada * ''Helianthus occidentalis'' Riddell – fewleaf sunflower, western sunflower – Great Lakes region, scattered in southeastern United States * ''Helianthus × orgyaloides'' CockerellColorado Kansas * ''Helianthus paradoxus'' Heiser – paradox sunflower – Utah New Mexico Texas * ''Helianthus pauciflorus'' Nutt. – stiff sunflower – central United States + Canada * ''Helianthus petiolaris'' Nutt. – prairie sunflower, lesser sunflower – much of United States + Canada * ''Helianthus porteri'' (A.Gray) Pruski – Porter's sunflower – Alabama Georgia South Carolina North Carolina * ''Helianthus praecox'' Engelm. & A.Gray Texas sunflower – Texas * †''Helianthus praetermissus''  – New Mexico sunflower – New Mexico† * ''Helianthus pumilus'' Nutt. – little sunflower – Colorado Wyoming Montana Utah Idaho * ''Helianthus radula'' (Pursh) Torr. & A.Gray – rayless sunflower – Louisiana Mississippi Alabama Georgia South Carolina Florida * ''Helianthus resinosus'' Small – resindot sunflower – Mississippi Alabama Georgia South Carolina North Carolina Florida * ''Helianthus salicifolius'' A.Dietr. – willowleaf sunflower – Texas Oklahoma Kansas Missouri Illinois Wisconsin Ohio Pennsylvania New York * ''Helianthus sarmentosus'' Rich.French Guiana * ''Helianthus scaberrimus'' ElliottSouth Carolina * ''Helianthus schweinitzii'' Torr. & A.Gray – Schweinitz's sunflower – South Carolina North Carolina * ''Helianthus silphioides'' Nutt. – rosinweed sunflower – Lower Mississippi Valley * ''Helianthus simulans'' E.Watson – muck sunflower – southeastern United States * ''Helianthus smithii'' Heiser – Smith's sunflower – Alabama Georgia Tennessee * ''Helianthus speciosus'' Hook.Michoacán * ''Helianthus strumosus'' L. – eastern + central United States + Canada * ''Helianthus subcanescens'' (A.Gray) E.WatsonManitoba, north-central United States * ''Helianthus subtuberosus'' Bourg. * ''Helianthus tuberosus'' L. – Jerusalem artichoke, sunchoke, earth-apple, topinambur – much of United States + Canada * ''Helianthus verticillatus'' Small – whorled sunflower – Alabama Georgia Tennessee


Formerly included


The following species were previously included in the genus ''Helianthus''. * ''Flourensia thurifera'' (Molina) DC. (as ''H. thurifer'' Molina) * ''Helianthella quinquenervis'' (Hook.) A.Gray (as ''H. quinquenervis'' Hook.) * ''Helianthella uniflora'' (Nutt.) Torr. & A.Gray (as ''H. uniflorus'' Nutt.) * ''Pappobolus imbaburensis'' (Hieron.) Panero (as ''H. imbaburensis'' Hieron.) * ''Viguiera procumbens'' (Pers.) S.F.Blake (as ''H. procumbens'' Pers.)


Gallery


File:Helianthus decapetalus 'Plenus'.jpg|''Helianthus decapetalus''
"Plenus" File:Sunflower leaf structure.jpg|Sunflower leaf structure File:Helianthus petiolaris (7161930155).jpg|Prairie sunflower
(''H. petiolaris'') File:Helianthus giganteus.jpg|Giant sunflower
(''H. giganteus'') File:Red sunflower.jpg|Red sunflower File:Sunflower "Strawberry Blonde" (3931552086).jpg|''Helianthus''
'Strawberry Blonde' File:Helianthus orgyalis0.jpg|Willowleaf sunflower
(''H. salicifolius'') File:Flower bud of Sunflower - Helianthus.JPG|Sunflower bud File:HelianthusTuberosus.jpg|Jerusalem artichoke
(''H. tuberosus'') File:Sunflower Leaf- Helianthus.JPG|Leaves of sunflower plant File:Side rear view of Sunflower head- Helianthus.JPG|Rear view of sunflower head File:Helianthus annuus - flower view 01.jpg|''H. annuus'' File:Helianthus x laetiflorus 001.JPG|''H. laetiflorus'' File:Redeed.jpg File:Sunflower_Kamand_DSC_2856.jpg|Close-up of a sunflower File:Семечко подсолнечника.jpg|Seed under a microscope


See also

* Spiral in the sunflower * Fermat's spiral * Phyllotaxis * Stegocintractia junci


References


{{Taxonbar|from=Q26949 Category:Asteraceae genera Category:Flora of North America Category:Crops