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Helianthus schweinitzii
''Helianthus schweinitzii'', known by the common name Schweinitz's sunflower, is a perennial wildflower endemic to the Piedmont physiographic province of North Carolina and South Carolina.〔(Biota of North America Program, 2014 county distribution map )〕 It is classified in the Sunflower Family (Asteraceae). Nationwide it is one of the rarest species of sunflower in the United States, but within its range it is not uncommon along utility and highway rights-of-way in North Carolina and South Carolina. There are only about 90 known populations, many containing less than 40 plants each. It was listed as a federal endangered species on May 7, 1991.〔(Hilton Pond Schweinitz Sunflower Recovery ). Retrieved on 2008-07-29.〕
Schweinitz's Sunflower grows from 1 to 4 m (40-160 inches) tall, producing tubers and rhizomes underground. Its stems are usually solitary, branching only at or above mid-stem. It flowers for about two to three weeks in early October. One plant generally produces 3-6 yellow flower heads, each with 8-15 ray florets surrounding 40 or more disc florets.〔(Flora of North America, ''Helianthus schweinitzii'' Torrey & A. Gray, 1842. Schweinitz’s sunflower )〕
The species is named for Lewis David von Schweinitz (1780-1834), a Salem, North Carolina clergyman and botanist who discovered the species. It was first described in 1842 by botanists John Torrey (1796-1873) and Asa Gray (1810-1888).〔(Torrey, John, + Asa Gray. 1842. Flora of North America 2(2): 330 )〕
It is believed by some that Schweinitz's Sunflower formerly occupied prairie-like habitats or Post Oak-Blackjack Oak savannas maintained by some degree of disturbance. Historically, this was provided by fire and/or native grazing animals such as Elk and American Bison, but these species were never common in North or South Carolina, so it is much more likely that suitable habitat was maintained by periodic controlled burns by native Americans. However, repeated mowing during the flowering and fruiting season is harmful to the species.〔(Hilton Pond Schweinitz Sunflower Recovery ). Retrieved on 2008-07-29.〕 Schweinitz's sunflower is known from a variety of soil types but is generally found growing on shallow, poor, clayey and/or rocky soils.〔 ("Schweinitz's Sunflower" ), U.S. Fish and Wildlife Service. Retrieved on 2008-07-29.〕
==References==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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