This occurs mostly from mid-western to mid-Atlantic states, but it is remarkably absent from the central and upper Ohio Valley (K). In Ky. it is largely restricted to regions where open woodland or grassland was maintained by fire before settlement. Parthenium has a remarkably clearcut northern limit within Appalachian regions; there are no records from PULA, ROCK, LAUR, KNOX and BELL. This limit may reflect the northern extent of more open fire-maintained woodland before settlement (Campbell et al. 1991). Several segregates have been described within this polyploid species (2n = 72), but they have not been recognized in most recent treatments (M, FNA 21). These include the relatively short, large-headed, hairy, broad-leaved and rhizomatous taxon, P. hispidum Raf., which should be investigated further (Mears 1975; Y). P. hispidum is largely midwestern, and typical of more base-rich soils (Ladd & Thomas 2015); it has also been reported from Ky. (BARR at CM) and Tenn., but verification is needed. The closely related P. auriculatum Britt. is reported from central Appalachian regions on calcareous soils; its basal leaves are relatively small and its cauline leaves are auriculate-clasping (W). Rafinesque (1836, 2:25-26) described three additional taxa in Parthenium of Ky. that did not become recognized at all by later authors: (1) angustifolium, "In the barrens or glades of West Kentucky"; (2) pumilum, "In the mts. Wasioto or Cumberland"; and (3) amplectans, "Glades of Kentucky." Did these perhaps match hispidum, auriculatum and integrifoilium (sensu stricto), respectively? Species of Parthenium contain sesquiterpene lactones (parthenin, parthenolide) with powerful physiological effects and traditional medicinal uses. P. integrifolium, or "wild quinine", was reputedly used by the U.S. Army to prevent malaria during World War One, but documentation is lacking. The true quinine and other anti-malarial quinoline alkaloids are largely restricted to Rubiaceae and Rutaceae (Michael 2007). More recent;ly, parthenolide has shown promise to alleviate effects of some cancers (e.g. Yang et al. 2013).