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2023-08-24T17:20:52Z

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{{Short description|Genus of flowering plants, the sunflowers}}
{{About|the genus Helianthus|the species of domesticated sunflower|Common sunflower||Sunflower (disambiguation)|and|Helianthus (disambiguation)}}
{{Automatic taxobox
| fossil_range =
| image = Sunflower sky backdrop.jpg
| image_caption = [[Helianthus annuus|Common sunflower]]
| display_parents = 3
| taxon = Helianthus
| authority = [[Carl Linnaeus|L.]]<ref name="GRIN">{{GRIN |access-date=22 February 2011}}</ref>
| synonyms_ref = <ref name="GRIN" /><ref name="WFO">{{cite web |url=http://www.worldfloraonline.org/taxon/wfo-4000017208 |title=''Helianthus'' L. |date=2023 |website=World Flora Online |publisher=World Flora Consortium |access-date=8 February 2023}}</ref>
| synonyms = ''Harpalium'' (Cass.) Cass.
}}

'''''Helianthus''''' ({{IPAc-en|ˌ|h|iː|l|i|ˈ|æ|n|θ|ə|s}})<ref>''Sunset Western Garden Book.'' Leisure Arts. 1995. pg. 606–607.</ref> is a [[genus]] comprising about 70 [[species]] of annual and perennial [[flowering plant]]s in the daisy family [[Asteraceae]] commonly known as '''sunflowers'''.<ref name=fna>{{eFloras|1|114871|Helianthus |tribe=Heliantheae |first=Edward E. |last=Schilling}}</ref><ref>{{cite web|title=Sunflower Production|url=https://www.ag.ndsu.edu/extensionentomology/recent-publications-main/publications/A-1331-sunflower-production-field-guide|publisher=North Dakota State University|access-date=12 July 2016|url-status=live|archive-url=https://web.archive.org/web/20160818082149/https://www.ag.ndsu.edu/extensionentomology/recent-publications-main/publications/A-1331-sunflower-production-field-guide|archive-date=18 August 2016}}</ref> Except for three [[South America]]n species, the species of ''Helianthus'' are native to [[North America]] and [[Central America]]. The best-known species is the [[common sunflower]] (''Helianthus annuus'').<ref name="SOED">{{cite book|title=Shorter Oxford English Dictionary |edition= 6th |year=2007 |location=United Kingdom |publisher=Oxford University Press |isbn=978-0-19-920687-2 |pages=3804}}</ref> This and other species, notably [[Jerusalem artichoke]] (''H. tuberosus''), are cultivated in [[temperateness|temperate]] regions and some [[tropical]] regions, as food crops for humans, cattle, and poultry, and as ornamental plants.<ref>{{cite book|title=RHS A-Z Encyclopedia of Garden Plants|year=2008|publisher=Dorling Kindersley|location=United Kingdom|isbn=978-1-4053-3296-5|pages=1136}}</ref> The species ''H. annuus'' typically grows during the summer and into early fall, with the peak growth season being mid-summer.<ref>{{cite web|title=Conservation Plant Characteristics - Helianthus annuus L. common sunflower HEAN3|url=https://plants.usda.gov/java/charProfile?symbol=HEAN3|work=USDA - Natural Resources Conservation Service|access-date=1 April 2019}}</ref>

Several [[perennial]] ''Helianthus'' species are grown in gardens, but have a tendency to spread rapidly and can become aggressive. On the other hand, 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 [[Silviculture|industrial forestry]] and [[pine]] plantations in Alabama, Georgia, and Tennessee. They grow to {{convert|6|ft|order=flip|abbr=off}} and are primarily found in woodlands, adjacent to creeks and moist, prairie-like areas.<ref>Remillard, Ashley (August 4, 2014) [http://www.endangeredspecieslawandpolicy.com/2014/08/articles/listing-decision/us-fish-and-wildlife-service-issues-final-rule-protecting-three-flowers/ "U.S. Fish and Wildlife Service Issues Final Rule Protecting Three Flowers"] {{webarchive|url=https://web.archive.org/web/20140812205455/http://www.endangeredspecieslawandpolicy.com/2014/08/articles/listing-decision/us-fish-and-wildlife-service-issues-final-rule-protecting-three-flowers/ |date=2014-08-12 }} ''Endangered Species Law and Policy Blog'', Nossaman LLP</ref>

The common sunflower is the national flower of [[Ukraine]], cultivated there for several centuries.<ref>{{cite web |last1=Sommerlad |first1=Joe |title=What Is The National Flower Of Ukraine? |url=https://www.independent.co.uk/news/world/europe/ukraine-what-is-national-flower-sunflower-b2054864.html |website=independent.co.uk |date=10 April 2022 |publisher=Independent |access-date=2022-08-03}}</ref>

== Description ==
[[File:Sunflower disk.jpg|thumb|The disk of a sunflower is made up of many little flowers. The ray flowers here are dried]]
[[File:I-40W-Sunflowers.jpg|thumb|In [[North Carolina]]|alt=A field of sunflowers in [[North Carolina]]]]
[[File:A sunflower seed growing.jpg|thumb|A sunflower seed growing]]
Sunflowers are usually tall [[annual plant|annual]] or perennial plants that in some species can grow to a height of {{convert|300|cm|in|abbr=off}} or more. Each "flower" is actually a disc made up of tiny flowers, to form a larger false flower to better attract pollinators. The plants bear one or more wide, terminal [[pseudanthium|capitula]] (flower heads made up of many tiny flowers), with bright yellow ray [[florets]] (mini flowers inside a flower head) at the outside and yellow or maroon (also known as a brown/red) disc florets inside. Several ornamental [[cultivars]] of ''[[Helianthus annuus|H. annuus]]'' have red-colored ray florets; all of them stem from a single original mutant.<ref>Heiser, C.B. ''The Sunflower''. University of Oklahoma Press. 1981.</ref> While the majority of sunflowers are yellow, there are branching varieties in other colours including, orange, red and purple.

The [[petiole (botany)|petiolate]] [[leaves]] are dentate and often sticky. The lower leaves are opposite, [[Glossary of leaf morphology#ovate|ovate]], or often heart-shaped. The rough and hairy [[Plant stem|stem]] is branched in the upper part in wild plants, but is usually unbranched in domesticated cultivars.<ref name="atamian"/>

This genus is distinguished technically by the fact that the ray florets (when present) are sterile, and by the presence on the disk flowers of a [[Pappus (flower structure)|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#In nature|spiral]].<ref>{{cite web |author=Ben Sparks |title=Geogebra: Sunflowers are irrationally pretty |url=https://www.geogebra.org/m/B4C9bbuy}}</ref>

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, ''[[Helianthus radula|H. radula]]'', lacks ray flowers altogether.

Overall, the macroevolution of the ''Helianthus'' is driven by multiple biotic and abiotic factors and influences various floral morphology.<ref>{{Cite journal |last1=Mason |first1=Chase M. |last2=Patel |first2=Hiral S. |last3=Davis |first3=Kaleigh E. |last4=Donovan |first4=Lisa A. |date=2017 |title=Beyond pollinators: evolution of floral architecture with environment across the wild sunflowers (Helianthus, Asteraceae) |journal=Plant Ecology and Evolution |volume=150 |issue=2 |pages=139–150 |doi=10.5091/plecevo.2017.1321 |issn=2032-3913 |jstor=44945441|doi-access=free }}{{free access}}</ref>

''Helianthus'' species are used as food plants by the [[larva]]e of [[list of Lepidoptera that feed on Helianthus|many lepidopterans]].

=== Growth stages ===
[[File:Sunflowers in Gahkuch Gilgit.jpg|thumb|right|In [[Gahkuch]], Pakistan]]
The growth of a sunflower depends strictly on its genetic makeup and background.<ref name="Sunflower Production">{{cite web |last1=Berglund |first1=Duane |title=Sunflower Production |url=https://www.ag.ndsu.edu/extensionentomology/recent-publications-main/publications/A-1331-sunflower-production-field-guide |access-date=Feb 7, 2019 |website=ag,ndsu |publisher=NDSU Extension Service and N.D. Agricultural Experiment Station}}</ref> 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.<ref name="Sunflower Production" />[[File:Helianthus whorl.jpg|thumb|Sunflower florets are arranged in a natural spiral having a [[Fibonacci number#Nature|Fibonacci sequence]]]]

=== Phylogeny ===
The geographical history of this genus 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.{{clarification needed|reason=bottlenecks result from reducing, not increasing genetic diversity |date=October 2022}} As a result, sunflower species are also experiencing a genetic bottleneck as a result of selective breeding for industrial use.<ref name="Park-2020">{{Cite journal |last1=Park |first1=Brian |last2=Burke |first2=John M. |date=2020-02-29 |title=Phylogeography and the Evolutionary History of Sunflower (Helianthus annuus L.): Wild Diversity and the Dynamics of Domestication |journal=Genes |language=en |volume=11 |issue=3 |pages=266 |doi=10.3390/genes11030266 |issn=2073-4425 |pmc=7140811 |pmid=32121324 |doi-access=free}}</ref>

=== Facing the Sun (heliotropism) ===
Before blooming, ''Helianthus'' plant heads tilt during the day to face the [[Sun]]. This movement is referred to as [[heliotropism]], which continues for a short time when flower buds form and young ''Helianthus'' heads track the Sun. At night, the flower heads reorient their position and face East in anticipation for the sunrise.<ref name="Vandenbrink-2014">{{Cite journal |last1=Vandenbrink |first1=Joshua P. |last2=Brown |first2=Evan A. |last3=Harmer |first3=Stacey L. |last4=Blackman |first4=Benjamin K. |date=July 2014 |title=Turning heads: The biology of solar tracking in sunflower |url=https://linkinghub.elsevier.com/retrieve/pii/S0168945214000818 |journal=Plant Science |language=en |volume=224 |pages=20–26 |doi=10.1016/j.plantsci.2014.04.006|pmid=24908502 |s2cid=887356 }}</ref> Sunflowers move back to their original position between 3am and 6am, and the leaves follow about an hour later.<ref name="Kutschera-2016">{{Cite journal |last1=Kutschera |first1=Ulrich |last2=Briggs |first2=Winslow R. |date=January 2016 |title=Phototropic solar tracking in sunflower plants: an integrative perspective |journal=Annals of Botany |language=en |volume=117 |issue=1 |pages=1–8 |doi=10.1093/aob/mcv141 |issn=0305-7364 |pmc=4701145 |pmid=26420201}}</ref>

By the time they are mature and reach [[anthesis]], ''Helianthus'' generally stop moving and remain facing east, which lets them be warmed by the rising sun.<ref name="atamian">{{cite journal | last1=Atamian | first1=Hagop S. | last2=Creux | first2=Nicky M. | last3=Brown | first3=Evan A. | last4=Garner | first4=Austin G. | last5=Blackman | first5=Benjamin K. | last6=Harmer | first6=Stacey L. | title=Circadian regulation of sunflower heliotropism, floral orientation, and pollinator visits | journal=Science| volume=353 | issue=6299 | date=2016-08-04 | issn=0036-8075 | doi=10.1126/science.aaf9793 | pages=587–590|pmid=27493185| bibcode=2016Sci...353..587A | doi-access=free }}</ref> Historically, this has led to controversy on whether or not ''Helianthus'' is heliotropic, as many scientists have failed to observe movement when studying plants that have already bloomed.<ref name="Vandenbrink-2014" />

This is notably different from heliotropism in leaves, as the moving mechanism for leaves exists in the [[pulvinus]]. Since flowers do not have pulvini, the movement is caused by increased growth rate of the stems.<ref name="Vandenbrink-2014" /><ref name="Atamian-2016">{{Cite journal |last1=Atamian |first1=Hagop S. |last2=Creux |first2=Nicky M. |last3=Brown |first3=Evan A. |last4=Garner |first4=Austin G. |last5=Blackman |first5=Benjamin K. |last6=Harmer |first6=Stacey L. |date=2016-08-05 |title=Circadian regulation of sunflower heliotropism, floral orientation, and pollinator visits |url=https://www.science.org/doi/10.1126/science.aaf9793 |journal=Science |language=en |volume=353 |issue=6299 |pages=587–590 |doi=10.1126/science.aaf9793 |pmid=27493185 |bibcode=2016Sci...353..587A |s2cid=206650484 |issn=0036-8075|doi-access=free }}</ref> The growth rate accumulation of the stem on the east side of the stem gradually pushes the flower from east to west during daytime. This matches with the Sun as it rises from the east and falls in the west. At night, the growth rate is higher in the west side of the stem that gradually pushes the flower from the west side back to the east side.<ref name="Atamian-2016" /> In addition, it is not actually the whole plant that changes its direction to face the Sun, but the flower itself that bends to be illuminated by the Suns rays.{{citation needed|date=June 2022}}

The heliotropic movement is caused by growth on the opposite side of the flower, driven by accumulation of growth hormones during Sun exposure.<ref name="atamian" /><ref>{{Cite web|title=How Sunflowers Move to Follow the Sun|url=https://nature.berkeley.edu/news/2016/08/sunflowers-move-clock|website=UC Berkeley Rausser College of Natural Resources|language=en|access-date=2020-05-01}}</ref>

Heliotropism persists on cloudy days when the sun is not shining brightly, meaning that the movement is [[Endogeny (biology)|endogenous]] as a trained and continuous process.<ref name="Vandenbrink-2014" /> However, flower movement does not occur during long periods of rain or clouds. It also does not occur in a growth chamber when exposed to 16 hours of light or in greenhouses, suggesting that the plants require a directional, moving light source.<ref name="Kutschera-2016" /><ref name="Vandenbrink-2014" /> Helianthus can also discriminate between different types of light.<ref name="Vandenbrink-2014" /> When exposed to different light frequencies, the [[hypocotyl]]s will bend toward blue light but not red light, depending on the quality of the light source.

It is the circadian rhythms and the differences of the stem growth rate that work together and cause the heliotropism of the ''Helianthus''. This is important for attracting pollinators and increasing growth metabolism. Future studies are needed for identifying the exact physiological basis and cellular mechanism for this behavior.

== Taxonomy ==
''Helianthus'' is derived from Greek {{lang|el|ἥλιος}} ''hēlios'' "sun" and {{lang|el|ἄνθος}} ''ánthos'' "flower",<ref>{{cite dictionary |title=helianthus |dictionary=An etymological dictionary of modern English |page=703 |url=https://archive.org/details/etymologicaldict00weekuoft/page/352/ |last1=Weekley |first1=Ernest |date=1921 |publisher=London J. Murray }}</ref> because its round flower heads in combination with the [[Asteraceae#Floral heads|ligules]] look like the [[Sun]].<ref name="SOED"/>

There are many species recognized in the genus:<ref name="WFO"/><ref>{{BONAP|ref|genus=Helianthus|archivedate=2014-11-02}}</ref>
{{div col}}
* ''[[Helianthus agrestis]]'' Pollard – southeastern sunflower – [[Florida]], [[Georgia (U.S. state)|Georgia]]
* ''[[Helianthus ambiguus]]'' Britt. – [[Wisconsin]], [[Michigan]], [[Ohio]], [[New York (state)|New York]]
* ''[[Helianthus angustifolius]]'' L. – swamp sunflower – [[Texas]], northern [[Florida]] to southern [[Illinois]], [[Long Island]], New York
* ''[[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.Watson – Texas, [[Indiana]], Ohio
* ''[[Helianthus californicus]]'' DC. – California sunflower – [[California]]
* ''[[Helianthus carnosus]]'' Small – lakeside sunflower – Florida
* ''[[Helianthus ciliaris]]'' DC. – Texas blueweed – United States: [[Washington (state)|Washington]], California, Arizona, New Mexico, Nevada, Utah, Texas, [[Oklahoma]], [[Colorado]], [[Kansas]], Illinois; Mexico: [[Tamaulipas]], [[Coahuila]], [[Chihuahua (state)|Chihuahua]], [[Sonora]]
* ''[[Helianthus cinereus]]'' Small – [[Missouri]], 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]]'' Sims – Missouri†
* ''[[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]]'' Small – Alabama, Kentucky, and Tennessee
* ''[[Helianthus exilis]]'' A.Gray – California
* ''[[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 of Texas to North Carolina
* ''[[Helianthus hirsutus]]'' Raf. – hairy sunflower – central and eastern United States, Ontario
* [[Helianthus × intermedius|''Helianthus'' × ''intermedius'']] R.W.Long – intermediate sunflower – scattered locales in United States
* ''[[Helianthus laciniatus]]'' A.Gray – alkali sunflower – United States: Arizona, New Mexico, Texas; Mexico: [[Coahuila]], [[Nuevo León]]
* [[Helianthus × laetiflorus|''Helianthus'' × ''laetiflorus'']] Pers. – cheerful sunflower, mountain sunflower – scattered in eastern and 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.Watson – [[Great Lakes]] region
* ''[[Helianthus maximiliani]]'' Schrad. – Maximillian sunflower – much of United States and Canada
* ''[[Helianthus membranifolius]]'' Poir. – [[French Guiana]]
* ''[[Helianthus microcephalus]]'' Torr. & A.Gray – eastern United States
* ''[[Helianthus mollis]]'' Lam. – downy sunflower, ashy sunflower – Ontario, eastern and 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 – United States: California, [[Arizona]]; Mexico: [[Baja California (state)|Baja California]], [[Baja California Sur]]
* ''[[Helianthus nuttallii]]'' Torr. & A.Gray – western and central United States, Canada
* ''[[Helianthus occidentalis]]'' Riddell – fewleaf sunflower, western sunflower – Great Lakes region, scattered in southeastern United States
* ''[[Helianthus × orgyaloides]]'' Cockerell – Colorado, 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]]'' Elliott – South 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 and central United States, Canada
* ''[[Helianthus subcanescens]]'' (A.Gray) E.Watson – [[Manitoba]], north-central United States
* ''[[Helianthus subtuberosus]]'' Bourg.
* ''[[Helianthus tuberosus]]'' L. – Jerusalem artichoke, sunchoke, earth-apple, topinambur – much of United States and Canada
* ''[[Helianthus verticillatus]]'' Small – whorled sunflower – Alabama, Georgia, Tennessee
{{div col end}}

===Formerly included===
The following species were previously included in the genus ''Helianthus''.<ref name="WFO"/>
* ''[[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.)

==Uses==
The [[Sunflower seed|seeds]] of ''H. annuus'' are used as human food. Most [[cultivar]]s of sunflower are variants of ''H. annuus'', but four other species (all [[perennial]]s) are also domesticated. This includes ''H. tuberosus'', the [[Jerusalem artichoke]], which produces edible tubers.

There are many species in the sunflower genus ''Helianthus'', and many species in other genera that may be called sunflowers.

* The Maximillian sunflower (''[[Helianthus maximiliani]]'') 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 sunchoke ([[Jerusalem artichoke]] or ''Helianthus tuberosus'') 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]]''.

==Ecology==
[[File:Sunflower Face.jpg|thumb|Bees pollinating a sunflower head]]
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.<ref name="Jones-2005">{{Cite journal|last1=Jones|first1=Gregory A.|last2=Gillett|first2=Jennifer L.|title=Intercropping with Sunflowers to Attract Beneficial Insects in Organic Agriculture|date=March 2005|journal=Florida Entomologist|language=en|volume=88|issue=1|pages=91–96|doi=10.1653/0015-4040(2005)088[0091:IWSTAB]2.0.CO;2|issn=0015-4040|doi-access=free}}</ref> 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 sunflower rows and crop vegetation plays an important role in this phenomenon, hypothesizing that closer proximity to the crops will increase insect attraction.<ref name="Jones-2005" />

In addition to pollinators of ''Helianthus spp''., there are other factors such as abiotic stress, [[Florivore|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.<ref name="Mason-2017">{{Cite journal|last1=Mason|first1=Chase M.|last2=Patel|first2=Hiral S.|last3=Davis|first3=Kaleigh E.|last4=Donovan|first4=Lisa A.|date=2017-07-10|title=Beyond pollinators: evolution of floral architecture with environment across the wild sunflowers (Helianthus, Asteraceae)|journal=Plant Ecology and Evolution|volume=150|issue=2|pages=139–150|doi=10.5091/plecevo.2017.1321|doi-access=free}}</ref>

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).<ref>{{Cite web|title=Abiotic & Biotic Factors in Ecosystems|url=https://sciencing.com/abiotic-biotic-factors-ecosystems-7146052.html|access-date=2021-02-20|website=Sciencing|language=en}}</ref>

It is thought that two biotic factors can explain for the evolution of larger sunflowers and why they are present in more drier environments.<ref name="Mason-2017" /> For one thing, the selection by pollinators is thought to have increased the sunflower’s size in a drier environment.<ref name="Mason-2017" /> This is because in a drier environment, there are typically less pollinators.<ref name="Mason-2017" /> 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.<ref name="Mason-2017" /> Another biotic factor that can explain for the evolution of larger sunflowers in drier environments is that the pressure from florivory and disease favors smaller flowers in habitats that have a more moderate supply of moisture (mesic habitat).<ref name="Mason-2017" /> Wetter environments usually have more dense vegetation, more herbivores, and more surrounding pathogens.<ref name="Mason-2017" /> 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.<ref name="Mason-2017" />

{{Clear}}

==Gallery==
<gallery mode="packed" heights="175">
File:Sunflower_Kamand_DSC_2856.jpg|Close-up of a sunflower head
File:Helianthus decapetalus 'Plenus'.jpg|''Helianthus decapetalus'' "Plenus"
File:Helianthus petiolaris (7161930155).jpg|[[helianthus petiolaris|Prairie sunflower]] (''H. petiolaris'')
File:Helianthus giganteus.jpg|[[Helianthus giganteus|Giant sunflower]] (''H. giganteus'')
File:HelianthusTuberosus.jpg|[[helianthus tuberosus|Jerusalem artichoke]] (''H. tuberosus'')
File:Helianthus x laetiflorus 001.JPG|''H. laetiflorus''
File:Helianthus orgyalis0.jpg|[[helianthus salicifolius|Willowleaf sunflower]] (''H. salicifolius'')
File:Helianthus annuus - flower view 01.jpg|''H. annuus''
File:Red sunflower.jpg|An orange-red sunflower
File:Redeed.jpg| A dark red sunflower cultivar
File:Sunflower "Strawberry Blonde" (3931552086).jpg|[[Helianthus 'Strawberry Blonde'|''Helianthus'' 'Strawberry Blonde']]
File:Flower bud of Sunflower - Helianthus.JPG|Sunflower bud
File:Side rear view of Sunflower head- Helianthus.JPG|Rear view of a sunflower head

File:Sunflower Leaf- Helianthus.JPG|Leaves of a sunflower plant
File:Sunflower leaf structure.jpg|Sunflower leaf structure
File:Семечко подсолнечника.jpg|Seed under a microscope
</gallery>

==See also==
* [[Fermat's spiral]]
* [[Phyllotaxis]]
* ''[[Stegocintractia junci]]''

==References==
{{Reflist}}
<references responsive="0" />

{{Taxonbar|from=Q26949}}

[[Category:Helianthus| ]]
[[Category:Asteraceae genera]]
[[Category:Flora of Northern America]]
[[Category:Crops]]
[[Category:Taxa named by Carl Linnaeus]]
[[Category:Crops originating from indigenous Americans]]

Helianthus - Revision history

Ajay Kumar at 17:20, 24 August 2023