Helianthus debilis

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Helianthus debilis
Tournesol de la Plage (5954050557).jpg

Secure (NatureServe)
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Genus: Helianthus
Species: H. debilis
Binomial name
Helianthus debilis
Nutt.
Synonyms[1]
  • Helianthus cucumerifolius Torr. & A.Gray, syn of subsp. cucumerifolius
  • Helianthus vestitus E.Watson, syn of subsp. vestitus

Helianthus debilis is a species of sunflower known by the common names cucumberleaf sunflower, beach sunflower, weak sunflower,[2] and East Coast dune sunflower.[3] It is native to the United States, where it can be found along the Atlantic and Gulf Coasts.[4] It is known elsewhere as an introduced species, such as South Africa, Australia, Taiwan, Slovakia, and Cuba.[5]

This species may be an annual or perennial herb.[4] It is usually perennial but it may last only one season in climates where freezes occur.[6] It can reach 2 meters tall. The stem grows from a taproot and may grow erect or decumbent.[4] It can also spread along the ground, becoming a dense groundcover.[6] The leaves are usually alternately arranged, and are variable in shape and size. The largest are up to 14 centimeters long by 13 wide. The showy inflorescence is a single flower head or an array of two or three heads. There are up to 30 lance-shaped phyllaries each up to 1.7 centimeters long. There are up to 20[4] or 21[7] ray florets, each up to 2.3 centimeters long. They are usually yellow in the wild, but cultivars have been bred to bear whitish,[7] reddish, or orange florets.[6] The center of the head is filled with many red, yellowish,[4] or purplish[7] disc florets. The fruit, a cypsela, is roughly 2 or 3 millimeters long.[4]

There are several subspecies. At one point there were eight.[8] Five are currently recognized.[1][4]

  • H. d. ssp. cucumerifolius - cucumberleaf sunflower. The subspecies with the widest distribution.[5][9]
  • H. d. ssp. debilis - beach sunflower. Endemic to Florida.[10][11]
  • H. d. ssp. silvestris - forest sunflower. Endemic to Texas.[12][13]
  • H. d. ssp. tardiflorus - slow-flowering sunflower. Mississippi to Florida.[14][15] Limited to rare, specialized coastal habitat.[16]
  • H. d. ssp. vestitus - clothed sunflower,[17] hairy beach sunflower.[18] Endemic to Florida.[19] Imperiled; known from about 22 occurrences.[18]

This species grows in several types of coastal habitat, sometimes directly on the beach. It tolerates a moderately saline environment, but not an excessive amount of salt spray or inundation.[20] It is highly drought-tolerant and it will grow in low-nutrient and poor soils, such as alkaline and acidic soils and sand.[6][7] The plant attracts butterflies and birds feed on the fruits.[6]

This plant is used as a garden flower. It is also good for landscaping, especially in poor, dry soils. It is planted on beaches, where it forms a sand-binding groundcover that prevents erosion and stabilizes dunes.[21] It requires supplemental watering only rarely, if ever. It may get "ratty-looking" after the showy flowers have withered.[20] Available cultivars include 'Italian White',[7] 'Flora Sun',[21]'Dazzler', 'Excelsior', and 'Orion'.[6]

Gallery[edit]

Dune Sunflowers growing in Miami Beach sand dunes (South Beach)

References[edit]

  1. ^ a b The Plant List, Helianthus debilis Nutt.
  2. ^ Helianthus debilis. Germplasm Resources Information Network.
  3. ^ Wunderlin, R. P. and B. F. Hansen. 2008. Helianthus debilis. Atlas of Florida Vascular Plants. Institute for Systematic Botany, University of South Florida, Tampa.
  4. ^ a b c d e f g Helianthus debilis. Flora of North America.
  5. ^ a b Helianthus debilis ssp. cucumerifolius. Germplasm Resources Information Network
  6. ^ a b c d e f Gilman, E. F. and S. Park-Brown. Helianthus debilis Beach Sunflower. Environmental Horticulture, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. 1999. Revised 2007.
  7. ^ a b c d e Christman, S. Helianthus debilis. Floridata.com. 1999. Updated 2003.
  8. ^ Wain, R. P. (1983). Genetic differentiation during speciation in the Helianthus debilis complex. Evolution 37(6) 1119-27.
  9. ^ Helianthus debilis ssp. cucumerifolius. Flora of North America.
  10. ^ Helianthus debilis ssp. debilis. Germplasm Resources Information Network.
  11. ^ Helianthus debilis ssp. debilis. Flora of North America.
  12. ^ Helianthus debilis ssp. silvestris. Germplasm Resources Information Network.
  13. ^ Helianthus debilis ssp. silvestris. Flora of North America.
  14. ^ Helianthus debilis ssp. tardiflorus. Germplasm Resources Information Network.
  15. ^ Helianthus debilis ssp. tardiflorus. Flora of North America.
  16. ^ Helianthus debilis ssp. tardiflorus. NatureServe.
  17. ^ Helianthus debilis ssp. vestitus. Germplasm Resources Information Network.
  18. ^ a b Helianthus debilis ssp. vestitus. NatureServe.
  19. ^ Helianthus debilis ssp. vestitus. Flora of North America.
  20. ^ a b Gann, G. D., et al. 2005-2013. East Coast dune sunflower Helianthus debilis. Natives For Your Neighborhood. The Institute for Regional Conservation. Delray Beach, Florida, USA.
  21. ^ a b Maura, C. and S. Sanders. Helianthus debilis ssp. debilis Plant Fact Sheet. USDA NRCS Brooksville Plant Materials Center. 2002.