Helianthus

Helianthus (/ˌhiːliˈænθəs/)[3] is a genus of plants comprising about 70 species.[4][5] Except for three species in South America, all Helianthus species 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.[6] 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.[7] The species H. annuus typically grows during the summer and into early fall, with the peak growth season being mid-summer.[8]

This article is about the genus Helianthus. For the common domesticated sunflower, see Helianthus annuus. For other uses, see Helianthus (disambiguation).
"Sunflower" and "sunflowers" redirect here. For other uses, see sunflower (disambiguation)

Sunflowers
Temporal range: Eocene-recent[1]
Common sunflower
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Subfamily: Asteroideae
Supertribe: Helianthodae
Tribe: Heliantheae
Genus: Helianthus
L.[2]
Synonyms[2]

Harpalium (Cass.) Cass.

Perennial sunflower species are not as common in garden use due to their tendency to spread rapidly and become invasive. 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 1.8 m (6 ft) and are primarily found in woodlands, adjacent to creeks and moist, prairie-like areas.[9]

Description
Close-up of a sunflower
The disk of a sunflower is made up of many little flowers. The ray flowers here are dried
A field of sunflowers in North Carolina
Sunflower florets are arranged in a natural spiral having a Fibonacci sequence

Origin

Sunflowers originate in the Americas. They were first domesticated in what is now Mexico and the Southern United States.[10][11] Domestic sunflower seeds have been found in Mexico, dating to 2100 BC. Native American people grew sunflowers as a crop from Mexico to Southern Canada.[11] In the 16th century the first crop breeds were brought from America to Europe by explorers.[11]

Morphology

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.[12] 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.[13] 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.[14] 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.[15]

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.[16] Additionally, the season it is planted will have effects on its development. 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.[16]

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.[17]

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.[18] 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.[19]

Top sunflower seed producers in 2018/2019[20]
Countries Million metric tonnes
Ukraine 15
Russia 13
European Union 10
Argentina 4
Turkey 2
Other 9

Diversity

Accepted species

There are many species recognized in the genus:[21][22]

Formerly included

The following species were previously included in the genus Helianthus.[21]

  • 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.)
  • Helianthus decapetalus
    "Plenus"
  • Sunflower leaf structure
  • Prairie sunflower
    (H. petiolaris)
  • Giant sunflower
    (H. giganteus)
  • Red sunflower
  • Helianthus
    'Strawberry Blonde'
  • Willowleaf sunflower
    (H. salicifolius)
  • Sunflower bud
  • Jerusalem artichoke
    (H. tuberosus)
  • Leaves of sunflower plant
  • Rear view of sunflower head
  • H. annuus
  • H. laetiflorus
  • Close-up of a sunflower
  • Seed under a microscope
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See also

References
  1. "Early sunflower family fossil found in South America". Phys.org. Lin Edwards.
  2. "Helianthus". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 2011-02-22.
  3. Sunset Western Garden Book. Leisure Arts. 1995. pg. 606–607.
  4. Schilling, Edward E. (2006). "Helianthus". In Flora of North America Editorial Committee (ed.). Flora of North America North of Mexico (FNA). 21. New York and Oxford – via eFloras.org, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
  5. "Sunflower Production". North Dakota State University. Archived from the original on August 18, 2016. Retrieved July 12, 2016.
  6. Shorter Oxford English Dictionary, 6th ed. United Kingdom: Oxford University Press. 2007. p. 3804. ISBN 978-0-19-920687-2.
  7. RHS A-Z Encyclopedia of Garden Plants. United Kingdom: Dorling Kindersley. 2008. p. 1136. ISBN 978-1-4053-3296-5.
  8. "Conservation Plant Characteristics - Helianthus annuus L. common sunflower HEAN3". USDA - Natural Resources Conservation Service. Retrieved April 1, 2019.
  9. 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
  10. Genetics, Genomics and Breeding of Sunflower, (CRC Press, 8 Apr 2010) edited by Jinguo Hu, Gerald Seiler, C. Kole, page 8
  11. Plant Evolution and the Origin of Crop Species, By James F. Hancock (CABI, 2012), page 188
  12. Heiser, C.B. The Sunflower. University of Oklahoma Press. 1981.
  13. "How Does a Sunflower Move?". Home Guides – SF Gate. Archived from the original on 2014-10-18.
  14. "How Sunflowers Move to Follow the Sun". UC Berkeley Rausser College of Natural Resources. Retrieved 2020-05-01.
  15. Ben Sparks. "Geogebra: Sunflowers are irrationally pretty".
  16. Berglund, Duane. "Sunflower Production". ag,ndsu. NDSU Extension Service and N.D. Agricultural Experiment Station. Retrieved Feb 7, 2019.
  17. Spinelli, D; Bardi, L; Fierro, A; Jez, S; Basosi, R (2017). "Environmental analysis of sunflower production with different forms of mineral nitrogen fertilizers" (PDF). The International Journal of Life Cycle Assessment. Journal of Environmental Management. 22 (4): 492–501. doi:10.1007/s11367-016-1089-6.
  18. Castro, C.; Leite, Regina. "Main aspects of sunflower production in Brazil". ProQuest 2036361008. Cite journal requires |journal= (help)
  19. Mastuura, M. I. S. F.; Dias, F. R. T.; Picoli, J. F.; Lucas, K. R. G.; Castro, C.; Hirakuri, M. H. (2017). "Life-cycle assessment of the soybean-sunflower production system in the Brazilian Cerrado" (PDF). The International Journal of Life Cycle Assessment. 22 (4): 492–501. doi:10.1007/s11367-016-1089-6.
  20. "Major producer countries of sunflower seed, 2018/2019". Statista. Retrieved 2018-08-10.
  21. "Helianthus". The Plant List. Missouri Botanical Garden. Royal Botanic Gardens, Kew.CS1 maint: others (link)
  22. "Helianthus". County-level distribution maps from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). 2014.
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