Helianthus or sunflower (from the Greek: ήλιος, Hēlios, "sun" and ανθός, anthos, "flower") L. /ˌhiːliˈænθəs/ is a genus of plants comprising about 70 species in the family Asteraceae. The genus is one of many in the Asteraceae that are known as sunflowers. Except for three species in South America, all Helianthus species are native to North America. The common name, "sunflower", typically refers to the popular annual species Helianthus annuus, or the common sunflower, 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 largest sunflower field is located in Tuscany, Italy.
The domesticated sunflower, H. annuus, is the most familiar species. Perennial sunflower species are not as popular for gardens due to their tendency to spread rapidly and become invasive. Whorled sunflowers, H. verticillatus, were 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 1.8 m (6 ft) and are primarily found in woodlands, adjacent to creeks and moist, prairie-like areas.
Sunflowers are usually tall annual or perennial plants that in some species can grow to a height of 300 cm (120 in) 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 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. Sunflowers are especially well known for their symmetry based on Fibonacci numbers and the golden angle.
Quite a bit of 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 agrestis – southeastern sunflower – Florida Georgia
- Helianthus ambiguus – Wisconsin Michigan Ohio New York State
- Helianthus angustifolius – swamp sunflower – Texas + Florida north to southern Illinois + Long Island
- Helianthus annuus – common sunflower, girasol – most of United States + Canada
- Helianthus anomalus – western sunflower – Nevada Utah Arizona New Mexico
- Helianthus argophyllus – silverleaf sunflower – Texas North Carolina Florida
- Helianthus arizonensis – Arizona sunflower – Arizona New Mexico
- Helianthus atrorubens – purpledisk sunflower – Louisiana Alabama Georgia Florida South Carolina North Carolina Tennessee Kentucky Virginia
- Helianthus bolanderi – serpentine sunflower – California Oregon
- Helianthus × brevifolius – Texas Indiana Ohio
- Helianthus californicus – California sunflower – California
- Helianthus carnosus – lakeside sunflower – Florida
- Helianthus ciliaris – Texas blueweed – Washington California Arizona New Mexico Nevada Utah Texas Oklahoma Colorado Kansas Illinois Tamaulipas Coahuila Chihuahua Sonora
- Helianthus cinereus – Missouri Kentucky Indiana Ohio
- Helianthus coloradensis – prairie sunflower – Colorado New Mexico
- Helianthus cusickii – Cusick's sunflower – Washington Oregon California Idaho Nevada
- Helianthus debilis – cucumberleaf Sunflower – Texas to Maine; Mississippi
- Helianthus decapetalus – thinleaf sunflower – eastern United States; Ontario Quebec
- Helianthus deserticola – desert sunflower – Arizona Nevada Utah
- †Helianthus diffusus – Missouri†
- Helianthus dissectifolius – Mexico
- Helianthus divaricatus – woodland sunflower or rough woodland sunflower – eastern United States; Ontario Quebec
- Helianthus × divariserratus Michigan Indiana Ohio Connecticut
- Helianthus × doronicoides – Texas Oklahoma Arkansas Missouri Iowa Minnesota Illinois Kentucky Indiana Ohio Pennsylvania Michigan New Jersey Virginia
- Helianthus eggertii – Alabama, Kentucky, and Tennessee
- Helianthus exilis – California
- Helianthus floridanus – Florida sunflower – Louisiana Alabama Georgia Florida South Carolina North Carolina
- Helianthus giganteus – giant sunflower – eastern United States; most of Canada
- Helianthus glaucophyllus – whiteleaf sunflower – Tennessee South Carolina North Carolina
- Helianthus × glaucus – scattered locales in southeastern United States
- Helianthus gracilentus – slender sunflower – California
- Helianthus grosseserratus – sawtooth sunflower – Great Plains, Great Lakes, Ontario Quebec
- Helianthus heterophyllus – variableleaf sunflower – Coastal Plain Texas to North Carolina
- Helianthus hirsutus – hairy sunflower – central + Eastern United States, Ontario
- Helianthus × intermedius – intermediate sunflower – scattered locales in United States
- Helianthus laciniatus – alkali sunflower – Arizona New Mexico Texas Coahuila Nuevo León
- Helianthus × laetiflorus – cheerful sunflower, mountain sunflower – scattered in eastern + central United States + Canada
- Helianthus laevigatus – smooth sunflower – Georgia South Carolina North Carolina Virginia Maryland West Virginia
- Helianthus lenticularis California Texas
- Helianthus longifolius – longleaf sunflower – Alabama Georgia North Carolina
- Helianthus × luxurians – Great Lakes region
- Helianthus maximiliani – Maximillian sunflower – much of United States + Canada
- Helianthus membranifolius – French Guiana
- Helianthus mollis – downy sunflower, ashy sunflower – Ontario, eastern + central United States
- Helianthus multiflorus – manyflower sunflower – Ohio
- Helianthus navarri – Chile
- Helianthus neglectus – neglected sunflower – New Mexico Texas
- Helianthus niveus – showy sunflower – California Arizona; Baja California, Baja California Sur
- Helianthus nuttallii western + central United States + Canada
- Helianthus occidentalis – fewleaf sunflower, western sunflower – Great Lakes region, scattered in southeastern United States
- Helianthus × orgyaloides – Colorado Kansas
- Helianthus paradoxus – paradox sunflower – Utah New Mexico Texas
- Helianthus pauciflorus – stiff sunflower – central United States + Canada
- Helianthus petiolaris – prairie sunflower, lesser sunflower – much of United States + Canada
- Helianthus porteri – Porter's sunflower – Alabama Georgia South Carolina North Carolina
- Helianthus praecox Texas sunflower – Texas
- †Helianthus praetermissus – New Mexico sunflower – New Mexico†
- Helianthus pumilus – little sunflower – Colorado Wyoming Montana Utah Idaho
- Helianthus radula – rayless sunflower – Louisiana Mississippi Alabama Georgia South Carolina Florida
- Helianthus resinosus – rescindot sunflower – Mississippi Alabama Georgia South Carolina North Carolina Florida
- Helianthus salicifolius – willowleaf sunflower – Texas Oklahoma Kansas Missouri Illinois Wisconsin Ohio Pennsylvania New York State
- Helianthus sarmentosus – French Guiana
- Helianthus scaberrimus – South Carolina
- Helianthus schweinitzii – Schweinitz's sunflower – South Carolina North Carolina
- Helianthus silphioides – rosinweed sunflower – Lower Mississippi Valley
- Helianthus simulans – muck sunflower – southeastern United States
- Helianthus smithii – Smith's sunflower – Alabama Georgia Tennessee
- Helianthus speciosus – Michoacán
- Helianthus strumosus – eastern + central United States + Canada
- Helianthus subcanescens – Manitoba, north-central United States
- Helianthus subtuberosus
- Helianthus tuberosus – Jerusalem artichoke, sunchoke, earth-apple, topinambur – much of United States + Canada
- Helianthus verticillatus – whorled sunflower – Alabama Georgia Tennessee
- Flourensia thurifera (as H. thurifer )
- Helianthella quinquenervis (as H. quinquenervis )
- Helianthella uniflora var. uniflora (as H. uniflorus )
- Pappobolus imbaburensis (as H. imbaburensis )
- Viguiera procumbens (as H. procumbens )
- ^ "Genus: Helianthus L". Germplasm Resources Information Network. United States Department of Agriculture. 2011-01-06. Retrieved 2011-02-22.
- ^ Sunset Western Garden Book. Leisure Arts. 1995. pg. 606–607.
- ^ Helianthus. Flora of North America.
- ^ "Sunflower Production". North Dakota State University. Retrieved July 12, 2016.
- ^ Shorter Oxford English Dictionary, 6th ed. United Kingdom: Oxford University Press. 2007. p. 3804. ISBN 0-19-920687-2.
- ^ RHS A-Z Encyclopedia of Garden Plants. United Kingdom: Dorling Kindersley. 2008. p. 1136. ISBN 1-4053-3296-4.
- ^ "Largest and Most Incredible Sunflower Field - Tuscany (Italy) | Tourism-Spot.com". tourism-spot.com. Archived from the original on 2016-10-19. Retrieved 2016-10-19.
- ^ Remillard, Ashley (August 4, 2014) "U.S. Fish and Wildlife Service Issues Final Rule Protecting Three Flowers" Archived 2014-08-12 at the Wayback Machine. Endangered Species Law and Policy Blog, Nossaman LLP
- ^ Heiser, C.B. The Sunflower. University of Oklahoma Press. 1981.
- ^ "How Does a Sunflower Move?". Home Guides – SF Gate.
- ^ The Plant List, search for Helianthus
- ^ "2013 Biota of North America Program 2014 county distribution maps". bonap.net.
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- Helianthus. On-line version of Flora North America, with key.