Torr. & A.Gray
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. It is classified in the Sunflower Family (Asteraceae). Nationwide it is one of the rarest plants 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.
Schweinitz's Sunflower grows from 1 to 4 m tall. Its stems are usually solitary, branching only at or above mid-stem. It flowers for about two to three weeks in early October. It is named for Lewis David von Schweinitz (1780-1834), a Salem, North Carolina clergyman and botanist who discovered the species. It was first described by botanists John Torrey (1796-1873) and Asa Gray (1810-1888).
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. Schweinitz's sunflower is known from a variety of soil types but is generally found growing on shallow, poor, clayey and/or rocky soils.