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Helianthus or sunflowers (from the Greek: ήλιος, [Hēlios], "sun" and ανθός, [hanthos], "flower") L. // is a genus of plants comprising about 52 species in the family Asteraceae, all of which are native to North America. The common name "sunflower" also applies to the popular annual species Helianthus annuus. This and other species, notably Jerusalem artichoke (H. tuberosus), are cultivated in temperate regions as food crops and ornamental plants.
The genus is one of many in the Asteraceae that are known as sunflowers. It is distinguished technically by the fact that the ray flowers, when present, are sterile, and by the presence on the disk flowers of a pappus that is of two awn-like scales that are cauducous (that is, easily detached and falling at maturity). Some species also have additional shorter scales in the pappus, and there is one species that 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.
There is quite a bit of variability among the perennial species that make up the bulk of the species 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.
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 six feet tall and are primarily found in woodlands, adjacent to creeks and moist, prairie-like areas.
Sunflowers are usually tall annuals, growing to a height of 50–390 centimetres (20–154 in).
The rough and hairy stem is branched in the upper part in wild plants but is usually unbranched in domesticated cultivars.
They bear one or several to many wide, terminal capitula (flower heads), with bright yellow ray florets at the outside and yellow or maroon disc florets inside. Several ornamental cultivars 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.
- Helianthus agrestis Pollard – southeastern sunflower
- Helianthus angustifolius L. – swamp sunflower
- Helianthus annuus L. – common sunflower, girasol (Spanish)
- Helianthus anomalus S.F.Blake – western sunflower
- Helianthus argophyllus Torr. & A.Gray – silverleaf sunflower
- Helianthus arizonensis R.C.Jacks. – Arizona sunflower
- Helianthus atrorubens L. – purpledisk sunflower
- Helianthus bolanderi A.Gray – serpentine sunflower
- Helianthus californicus DC. – California sunflower
- Helianthus carnosus Small – lakeside sunflower
- Helianthus ciliaris DC. – Texas blueweed
- Helianthus cinereus
- Helianthus couplandii – prairie sunflower
- Helianthus cusickii A.Gray – Cusick's sunflower
- Helianthus debilis Nutt. – cucumberleaf Sunflower
- H. debilis ssp. cucumerifolius (Torr. & A.Gray) Heiser – cucumberleaf sunflower
- H. debilis ssp. debilis – beach sunflower, dune sunflower
- H. debilis ssp. silvestris Heiser – cucumberleaf sunflower
- H. debilis ssp. tardiflorus Heiser – cucumberleaf sunflower
- H. debilis ssp. vestitus (E.Watson) Heiser – cucumberleaf sunflower
- Helianthus decapetalus L. – thinleaf sunflower
- Helianthus deserticola Heiser – desert sunflower
- Helianthus divaricatus L. – woodland sunflower or rough woodland sunflower
- Helianthus eggertii Small – Eggert's sunflower
- Helianthus floridanus A.Gray ex Chapm. – Florida sunflower
- Helianthus giganteus L. – giant sunflower
- Helianthus glaucophyllus D.M.Sm – whiteleaf sunflower
- Helianthus gracilentus A.Gray – slender sunflower
- Helianthus grosseserratus M.Martens – sawtooth sunflower
- Helianthus heterophyllus Nutt. – variableleaf sunflower
- Helianthus hirsutus Raf. – hairy sunflower
- Helianthus × intermedius R.W.Long – intermediate sunflower
- Helianthus laciniatus A.Gray – alkali sunflower
- Helianthus × laetiflorus Pers. – cheerful sunflower, mountain sunflower
- Helianthus laevigatus Torr. & A.Gray – smooth sunflower
- Helianthus longifolius Pursh – longleaf sunflower
- Helianthus maximiliani Schrad. – Maximillian sunflower
- Helianthus microcephalus Torr. & A.Gray – small woodland sunflower
- Helianthus mollis Lam. – downy sunflower, ashy sunflower
- Helianthus × multiflorus L. – manyflower sunflower
- Helianthus neglectus Heiser – neglected sunflower
- Helianthus niveus (Benth.) Brandegee – showy sunflower
- Helianthus nuttallii Torr. & A.Gray – Nuttall's sunflower
- Helianthus occidentalis Riddell – fewleaf sunflower, western sunflower
- Helianthus paradoxus Heiser – paradox sunflower
- Helianthus pauciflorus Nutt. – stiff sunflower
- Helianthus petiolaris Nutt. – prairie sunflower, lesser sunflower
- Helianthus porteri (A.Gray) Pruski – Porter's sunflower
- Helianthus praecox Engelm. & A.Gray Texas sunflower
- Helianthus praetermissus – New Mexico sunflower
- Helianthus pumilus Nutt. – little sunflower
- Helianthus radula (Pursh) Torr. & A.Gray – rayless sunflower
- Helianthus resinosus Small – rescindot sunflower
- Helianthus salicifolius A.Dietr. – willowleaf sunflower
- Helianthus schweinitzii Torr. & A.Gray – Schweinitz's sunflower
- Helianthus silphioides Nutt. – rosinweed sunflower
- Helianthus simulans E.Watson – muck sunflower
- Helianthus smithii Heiser – Smith's sunflower
- Helianthus strumosus L. – paleleaf woodland sunflower
- Helianthus tuberosus L. – Jerusalem artichoke, sunchoke, earth-apple, topinambur
- Helianthus verticillatus Small – whorled sunflower
Formerly placed here
- Flourensia thurifera (Molina) DC. (as H. thurifer Molina)
- Helianthella quinquenervis (Hook.) A.Gray (as H. quinquenervis Hook.)
- Helianthella uniflora var. uniflora (as H. uniflorus Nutt.)
- Pappobolus imbaburensis (Hieron.) Panero (as H. imbaburensis Hieron.)
- Tithonia rotundifolia (Mill.) S.F.Blake (as H. speciosus Hook.)
- Viguiera procumbens (Pers.) S.F.Blake (as H. procumbens Pers.)
- "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.
- Shorter Oxford English Dictionary, 6th ed. United Kingdom: Oxford University Press. 2007. p. 3804. ISBN 0199206872.
- RHS A-Z Encyclopedia of Garden Plants. United Kingdom: Dorling Kindersley. 2008. p. 1136. ISBN 1405332964.
- Remillard, Ashley (August 4, 2014) "U.S. Fish and Wildlife Service Issues Final Rule Protecting Three Flowers" Endangered Species Law and Policy Blog, Nossaman LLP
- Heiser, C. B. The Sunflower. University of Oklahoma Press. 1981.
- "GRIN Species Records of Helianthus". Germplasm Resources Information Network. United States Department of Agriculture. Retrieved 2011-02-22.
- "Helianthus". Integrated Taxonomic Information System. Retrieved 2011-02-22.