Helianthus L. pron.: // (sunflower) is a genus of plants comprising 52 species in the Asteraceae family, 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 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.
A key to identify the species and a comprehensive listing of species can be found in the Flora North America treatment.
The domesticated sunflower, Helianthus annuus, is the most familiar species. These are usually tall annuals, growing to a height of 50-390 or more cm. 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. The upper leaves are alternate and narrower. 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 recently become popular that have red-colored ray florets, all of these stem from a single original mutant). These flower heads follow the direction of the sun, going from east to west during the day.
- 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.
- 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
- Helianthus debilis ssp. cucumerifolius (Torr. & A.Gray) Heiser – Cucumberleaf Sunflower
- Helianthus debilis ssp. debilis – Beach Sunflower, Dune Sunflower
- Helianthus debilis ssp. silvestris Heiser – Cucumberleaf Sunflower
- Helianthus debilis ssp. tardiflorus Heiser – Cucumberleaf Sunflower
- Helianthus debilis ssp. vestitus (E.Watson) Heiser – Cucumberleaf Sunflower
- Helianthus decapetalus L. – Thinleaf Sunflower
- Helianthus deserticola Heiser
- Helianthus divaricatus L. – Woodland Sunflower
- Helianthus eggertii Small – Eggert's Sunflower
- Helianthus floridanus A.Gray ex Chapm. – Florida Sunflower
- Helianthus giganteus L.
- 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.
- 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.
- Helianthus neglectus Heiser – Neglected Sunflower
- Helianthus niveus (Benth.) Brandegee
- Helianthus nuttallii Torr. & A.Gray
- Helianthus occidentalis Riddell – Fewleaf Sunflower
- Helianthus paradoxus Heiser – Paradox Sunflower
- Helianthus pauciflorus Nutt.
- Helianthus petiolaris Nutt.
- Helianthus porteri (A.Gray) Pruski – Porter's Sunflower
- Helianthus praecox Engelm. & A.Gray
- Helianthus praetermissus – New Mexico Sunflower
- Helianthus pumilus Nutt. – Little Sunflower
- Helianthus radula (Pursh) Torr. & A.Gray – Rayless Sunflower
- Helianthus resinosus Small – Resindot 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
- Helianthus verticillatus Small
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.)
|Wikimedia Commons has media related to: Helianthus|
|Wikispecies has information related to: Helianthus|
- "Genus: Helianthus L.". Germplasm Resources Information Network. United States Department of Agriculture. 2011-01-06. http://www.ars-grin.gov/cgi-bin/npgs/html/genus.pl?5474. Retrieved 2011-02-22.
- Sunset Western Garden Book, 1995:606–607
- Shorter Oxford English dictionary, 6th ed.. United Kingdom: Oxford University Press. 2007. pp. 3804. ISBN 0199206872.
- RHS A-Z encyclopedia of garden plants. United Kingdom: Dorling Kindersley. 2008. pp. 1136. ISBN 1405332964.
- Flora North America treatment vol. 21 pages 141-169, 2006
- Heiser, C. B. 1981. The Sunflower. University of Oklahoma Press.
- "GRIN Species Records of Helianthus". Germplasm Resources Information Network. United States Department of Agriculture. http://www.ars-grin.gov/cgi-bin/npgs/html/splist.pl?5474. Retrieved 2011-02-22.
- "Helianthus". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=36611. Retrieved 2011-02-22.