Helianthus

Sunflowers
Common sunflower
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
Order: Asterales
Family: Asteraceae
Subfamily: Asteroideae
Tribe: Heliantheae
Genus: Helianthus
L.[1]
Synonyms[1]

Harpalium (Cass.) Cass.

Helianthus or sunflowers (from the Greek: ήλιος, Hēlios, "sun" and ανθός, anthos, "flower") L. /ˌhiːliˈænθəs/[2] is a genus of plants comprising about 70 species[3] in the family Asteraceae.[4] 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.[5] This and other species, notably Jerusalem artichoke (H. tuberosus), are cultivated in temperate regions as food crops for cattle and poultry and ornamental plants.[6] The largest sunflower field is located in Tuscany, Italy. [7]

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.[8]

Description

Close-up of a sunflower
Close-up of a sunflower
The disk of a sunflower is made up of many little flowers. The ray flowers here are dried up.
A field of sunflowers in North Carolina.

Sunflowers are usually tall annual or perennial plants that grow to a height of 300 centimetres (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 Helianthus annuus have red-colored ray florets; all of them stem from a single original mutant.[9] 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.[10] 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 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. Sunflowers are especially well known for their symmetry based on Fibonacci numbers and the Golden angle.

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.

Helianthus species are used as food plants by the larvae of many lepidopterans. The seeds of the species Helianthus annuus are used as human food.

Diversity

Accepted species[11][12]
  1. Helianthus agrestis Pollard – southeastern sunflower – Florida Georgia
  2. Helianthus ambiguus Britt. – Wisconsin Michigan Ohio New York State
  3. Helianthus angustifolius L. – swamp sunflower – Texas + Florida north to southern Illinois + Long Island
  4. Helianthus annuus L. – common sunflower, girasol – most of United States + Canada
  5. Helianthus anomalus S.F.Blake – western sunflower – Nevada Utah Arizona New Mexico
  6. Helianthus argophyllus Torr. & A.Gray – silverleaf sunflower – Texas North Carolina Florida
  7. Helianthus arizonensis R.C.Jacks. – Arizona sunflower – Arizona New Mexico
  8. Helianthus atrorubens L. – purpledisk sunflower – Louisiana Alabama Georgia Florida South Carolina North Carolina Tennessee Kentucky Virginia
  9. Helianthus bolanderi A.Gray – serpentine sunflower – California Oregon
  10. Helianthus × brevifolius E.Watson – Texas Indiana Ohio
  11. Helianthus californicus DC. – California sunflower – California
  12. Helianthus carnosus Small – lakeside sunflower – Florida
  13. Helianthus ciliaris DC. – Texas blueweed – Washington California Arizona New Mexico Nevada Utah Texas Oklahoma Colorado Kansas Illinois Tamaulipas Coahuila Chihuahua Sonora
  14. Helianthus cinereus Small – Missouri Kentucky Indiana Ohio
  15. Helianthus coloradensis Cockerell – prairie sunflower – Colorado New Mexico
  16. Helianthus cusickii A.Gray – Cusick's sunflower – Washington Oregon California Idaho Nevada
  17. Helianthus debilis Nutt. – cucumberleaf Sunflower – Texas to Maine; Mississippi
  18. Helianthus decapetalus L. – thinleaf sunflower – eastern United States; Ontario Quebec
  19. Helianthus deserticola Heiser – desert sunflower – Arizona Nevada Utah
  20. †Helianthus diffusus Sims – Missouri†
  21. Helianthus dissectifolius R.C.Jacks. – Mexico
  22. Helianthus divaricatus L. – woodland sunflower or rough woodland sunflower – eastern United States; Ontario Quebec
  23. Helianthus × divariserratus R.W.Long Michigan Indiana Ohio Connecticut
  24. Helianthus × doronicoides Lam. – Texas Oklahoma Arkansas Missouri Iowa Minnesota Illinois Kentucky Indiana Ohio Pennsylvania Michigan New Jersey Virginia
  25. Helianthus eggertii Small – Alabama, Kentucky, and Tennessee
  26. Helianthus exilis A.Gray – California
  27. Helianthus floridanus A.Gray ex Chapm. – Florida sunflower – Louisiana Alabama Georgia Florida South Carolina North Carolina
  28. Helianthus giganteus L. – giant sunflower – eastern United States; most of Canada
  29. Helianthus glaucophyllus D.M.Sm – whiteleaf sunflower – Tennessee South Carolina North Carolina
  30. Helianthus × glaucus Small – scattered locales in southeastern United States
  31. Helianthus gracilentus A.Gray – slender sunflower – California
  32. Helianthus grosseserratus M.Martens – sawtooth sunflower – Great Plains, Great Lakes, Ontario Quebec
  33. Helianthus heterophyllus Nutt. – variableleaf sunflower – Coastal Plain Texas to North Carolina
  34. Helianthus hirsutus Raf. – hairy sunflower – central + Eastern United States, Ontario
  35. Helianthus × intermedius R.W.Long – intermediate sunflower – scattered locales in United States
  36. Helianthus laciniatus A.Gray – alkali sunflower – Arizona New Mexico Texas Coahuila Nuevo León
  37. Helianthus × laetiflorus Pers. – cheerful sunflower, mountain sunflower – scattered in eastern + central United States + Canada
  38. Helianthus laevigatus Torr. & A.Gray – smooth sunflower – Georgia South Carolina North Carolina Virginia Maryland West Virginia
  39. Helianthus lenticularis Douglas ex Lindl. California Texas
  40. Helianthus longifolius Pursh – longleaf sunflower – Alabama Georgia North Carolina
  41. Helianthus × luxurians (E.Watson) E.Watson – Great Lakes region
  42. Helianthus maximiliani Schrad. – Maximillian sunflower – much of United States + Canada
  43. Helianthus membranifolius Poir. – French Guiana
  44. Helianthus mollis Lam. – downy sunflower, ashy sunflower – Ontario, eastern + central United States
  45. Helianthus multiflorus L. – manyflower sunflower – Ohio
  46. Helianthus navarri Phil. – Chile
  47. Helianthus neglectus Heiser – neglected sunflower – New Mexico Texas
  48. Helianthus niveus (Benth.) Brandegee – showy sunflower – California Arizona; Baja California, Baja California Sur
  49. Helianthus nuttallii Torr. & A.Gray – western + central United States + Canada
  50. Helianthus occidentalis Riddell – fewleaf sunflower, western sunflower – Great Lakes region, scattered in southeastern United States
  51. Helianthus × orgyaloides Cockerell – Colorado Kansas
  52. Helianthus paradoxus Heiser – paradox sunflower – Utah New Mexico Texas
  53. Helianthus pauciflorus Nutt. – stiff sunflower – central United States + Canada
  54. Helianthus petiolaris Nutt. – prairie sunflower, lesser sunflower – much of United States + Canada
  55. Helianthus porteri (A.Gray) Pruski – Porter's sunflower – Alabama Georgia South Carolina North Carolina
  56. Helianthus praecox Engelm. & A.Gray Texas sunflower – Texas
  57. †Helianthus praetermissus  – New Mexico sunflower – New Mexico†
  58. Helianthus pumilus Nutt. – little sunflower – Colorado Wyoming Montana Utah Idaho
  59. Helianthus radula (Pursh) Torr. & A.Gray – rayless sunflower – Louisiana Mississippi Alabama Georgia South Carolina Florida
  60. Helianthus resinosus Small – rescindot sunflower – Mississippi Alabama Georgia South Carolina North Carolina Florida
  61. Helianthus salicifolius A.Dietr. – willowleaf sunflower – Texas Oklahoma Kansas Missouri Illinois Wisconsin Ohio Pennsylvania New York State
  62. Helianthus sarmentosus Rich. – French Guiana
  63. Helianthus scaberrimus Elliott – South Carolina
  64. Helianthus schweinitzii Torr. & A.Gray – Schweinitz's sunflower – South Carolina North Carolina
  65. Helianthus silphioides Nutt. – rosinweed sunflower – Lower Mississippi Valley
  66. Helianthus simulans E.Watson – muck sunflower – southeastern United States
  67. Helianthus smithii Heiser – Smith's sunflower – Alabama Georgia Tennessee
  68. Helianthus speciosus Hook. – Michoacán
  69. Helianthus strumosus L. – eastern + central United States + Canada
  70. Helianthus subcanescens (A.Gray) E.Watson – Manitoba, north-central United States
  71. Helianthus subtuberosus Bourg.
  72. Helianthus tuberosus L. – Jerusalem artichoke, sunchoke, earth-apple, topinambur – much of United States + Canada
  73. Helianthus verticillatus Small – whorled sunflower – Alabama Georgia Tennessee
Formerly included[11]

References

  1. 1 2 "Genus: Helianthus L.". Germplasm Resources Information Network. United States Department of Agriculture. 2011-01-06. Retrieved 2011-02-22.
  2. ↑ Sunset Western Garden Book. Leisure Arts. 1995. pg. 606–607.
  3. ↑ Helianthus. Flora of North America.
  4. ↑ "Sunflower Production". North Dakota State University. Retrieved July 12, 2016.
  5. ↑ Shorter Oxford English Dictionary, 6th ed. United Kingdom: Oxford University Press. 2007. p. 3804. ISBN 0-19-920687-2.
  6. ↑ RHS A-Z Encyclopedia of Garden Plants. United Kingdom: Dorling Kindersley. 2008. p. 1136. ISBN 1-4053-3296-4.
  7. ↑ "Largest and Most Incredible Sunflower Field - Tuscany (Italy) | Tourism-Spot.com". tourism-spot.com. Retrieved 2016-10-19.
  8. ↑ 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
  9. ↑ Heiser, C.B. The Sunflower. University of Oklahoma Press. 1981.
  10. ↑ "How Does a Sunflower Move?". Home Guides – SF Gate.
  11. 1 2 The Plant List, search for Helianthus
  12. ↑ "2013 Biota of North America Program 2014 county distribution maps". bonap.net.
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