About Eupatorium rotundifolium var. scabridum (Elliott) A.Gray
This taxon is the variety scabridum of round-leaved thoroughwort, with the accepted scientific name Eupatorium rotundifolium var. scabridum (Elliott) A.Gray. Stems grow up to 100 cm (40 inches) tall and develop from short rhizomes. Its inflorescences are made up of many small white flower heads; each flower head contains 5 disc florets and has no ray florets. Individual plants of this species can vary widely in their traits because of widespread hybridization. The species Eupatorium rotundifolium ranges across eastern and central North America, occurring from Massachusetts, New York, Indiana, and Oklahoma in the north, southward to southern Florida and Texas. It grows in a variety of habitats that range from moist to dry: these include woodlands, pine savannas, seepage bogs, and roadside verges. Chemically, Eupatorium rotundifolium contains guaianolide-type sesquiterpene lactones, specifically euparotin acetate and eupachlorin acetate. When these two compounds are isolated from the plant, they inhibit tumor growth in laboratory in vitro cultures. Historically, this plant was used medicinally to treat intermittent fevers.
