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 a height of 2 meters. 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 arranged alternately 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]

• Helianthus debilis subsp. cucumerifolius - cucumberleaf sunflower. The subspecies with the widest distribution.^[5][9]
• Helianthus debilis subsp. debilis - beach sunflower. Endemic to Florida.^[10][11]
• Helianthus debilis subsp. silvestris - forest sunflower. Endemic to Texas.^[12][13]
• Helianthus debilis subsp. tardiflorus - slow-flowering sunflower. Mississippi to Florida.^[14][15] Limited to rare, specialized coastal habitat.^[16]
• Helianthus debilis subsp. 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]

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

• 
  Sea Grapes and Dune Sunflowers
• 
  Dune Sunflower Closeup