Helianthus

Helianthus
Sunflower (Helianthus annuus)
Scientific classification
Kingdom: Plantae (unranked): Angiosperms (unranked): Eudicots (unranked): Asterids Order: Asterales Family: Asteraceae Subfamily: Helianthoideae Tribe: Heliantheae Genus: Helianthus L.
Species
See text.

The genus Helianthus L. (pronounced /ˌhiːliˈænθəs/)^[1] comprises 52 species and several subspecies in the Asteraceae family, all of which are native to North America, with some species (particularly Helianthus annuus (sunflower) and Helianthus tuberosus (Jerusalem artichoke) cultivated in Europe and other parts of the world 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 ^[2].

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^[3]). These flower heads follow the direction of the sun, going from east to west during the day.

Helianthus species are used as food plants by the larvae of some Lepidoptera species (see list of Lepidoptera that feed on Helianthus).

Species

• Helianthus agrestis : Southeastern Sunflower
• Helianthus angustifolius : Swamp Sunflower
• Helianthus annuus : Common Sunflower, Girasol (Spanish)
• Helianthus anomalus : Western Sunflower
• Helianthus argophyllus  : Silverleaf Sunflower
• Helianthus arizonensis : Arizona Sunflower
• Helianthus atrorubens
• Helianthus bolanderi : Serpentine Sunflower
• Helianthus californicus : California Sunflower
• Helianthus carnosus : Lakeside Sunflower
• Helianthus ciliaris : Texas Blueweed
• Helianthus cinereus
• Helianthus couplandii : Prairie Sunflower
• Helianthus cusickii : Cusick's Sunflower

Prairie Sunflower (Helianthus petiolaris)

• Helianthus debilis : Cucumberleaf Sunflower
  • Helianthus debilis ssp. cucumerifolius : Cucumberleaf Sunflower
  • Helianthus debelis ssp. debilis : Beach Sunflower, Dune Sunflower
  • Helianthus debilis ssp. silvestris : Cucumberleaf Sunflower
  • Helianthus debilis ssp. tardiflorus : Cucumberleaf Sunflower
  • Helianthus debilis ssp. vestitus : Cucumberleaf Sunflower
• Helianthus decapetalus : Thinleaf Sunflower
• Helianthus deserticola
• Helianthus divaricatus : Woodland Sunflower
• Helianthus eggertii : Eggert's Sunflower
• Helianthus floridanus : Florida Sunflower
• Helianthus giganteus
• Helianthus glaucophyllus : Whiteleaf Sunflower
• Helianthus gracilentus : Slender Sunflower
• Helianthus grosseserratus: Sawtooth Sunflower
• Helianthus heterophyllus : Variableleaf Sunflower
• Helianthus hirsutus
• Helianthus laciniatus : Alkali Sunflower
• Helianthus laetiflorus
• Helianthus laevigatus : Smooth Sunflower
• Helianthus longifolius : Longleaf Sunflower

Willowleaf Sunflower (Helianthus salicifolius)

• Helianthus maximiliani : Maximillian Sunflower
• Helianthus microcephalus : Small Woodland Sunflower
• Helianthus mollis
• Helianthus multiflorus
• Helianthus neglectus : Neglected Sunflower
• Helianthus niveus
  • Helianthus niveus ssp. canescens : Showy Sunflower
  • Helianthus niveus ssp. tephrodes : Algodones Sunflower
• Helianthus nuttallii
  • Helianthus nuttallii ssp. nuttallii : Nuttall's Sunflower
  • Helianthus nuttallii ssp. parishii : Parish's Sunflower
  • Helianthus nuttallii ssp. Rydbergii : Rydberg's Sunflower
• Helianthus occidentalis : Fewleaf Sunflower
  • Helianthus occidentalis ssp. occidentalis : Fewleaf Sunflower
  • Helianthus occidentalis ssp. plantagineus : Fewleaf Sunflower
• Helianthus paradoxus : Paradox Sunflower
• Helianthus pauciflorus
  • Helianthus pauciflorus ssp. pauciflorus : Stiff Sunflower
  • Helianthus pauciflorus ssp. subrhomboideus : Stiff Sunflower
• Helianthus petiolaris
  • Helianthus petiolaris ssp. fallax : Prairie Sunflower
  • Helianthus petiolaris ssp. petiolaris : Prairie Sunflower
• Helianthus porteri : Porter's Sunflower
• Helianthus praecox
  • Helianthus praecox ssp. hirtus : Texas Sunflower
  • Helianthus praecox ssp. praecox  : Texas Sunflower
  • Helianthus praecox ssp. runyonii : Runyon's Sunflower

Jerusalem Artichoke (Helianthus tuberosus)

• Helianthus praetermissus : New Mexico Sunflower
• Helianthus pumilus : Little Sunflower
• Helianthus radula : Rayless Sunflower
• Helianthus resinosus : Resindot Sunflower
• Helianthus salicifolius : Willowleaf Sunflower
• Helianthus schweinitzii : Schweinitz's Sunflower
• Helianthus silphioides : Rosinweed Sunflower
• Helianthus simulans : Muck Sunflower
• Helianthus smithii : Smith's Sunflower
• Helianthus strumosus  : Paleleaf Woodland Sunflower
• Helianthus tuberosus : Jerusalem Artichoke, Sunchoke

References

External links

• [1] on-line version of Flora North America treatment of Helianthus
• See here for a more complete list of species

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