Eupatorium rotundifolium, commonly called roundleaf thoroughwort, is a North American species of plant in the family Asteraceae. It native to the eastern and central United States, in all the coastal states from Maine to Texas, and inland as far as Missouri and the Ohio Valley.Biota of North America Program 2014 county distribution map It is found in low, moist habitats such as wet savannas and bogs.Flora of North America, Eupatorium rotundifolium Linnaeus, 1753. Roundleaf thoroughwort
Description The stems up to 100 cm (40 inches) tall and are produced from short rhizomes. The inflorescences are composed of a large number of small white flower heads, each with 5 disc florets but no ray florets. Plants can be highly variable due to hybridization.
Distribution and habitat Eupatorium rotundifolium is found from Massachusetts, New York, Indiana, and Oklahoma south to southern Florida and Texas. It grows in moist to dry woodlands, pine savannas, seepage bogs, as well as along roadsides. Taxonomy Three varieties of Eupatorium rotundifolium are recognized. They are: Eupatorium rotundifolium var. ovatum (Bigelow) Torr. Eupatorium rotundifolium var. rotundifolium Eupatorium rotundifolium var. scabridum (Elliott) A.Gray
The plants known as Eupatorium rotundifolium var. saundersii have often been treated as a variety of E. rotundifolium. They can be distinguished based on morphology, and molecular evidence also suggests that these plants may be different enough from E. rotundifolium to recognize them as a species, Eupatorium pilosum.
Hybridization As is common in Eupatorium, E. rotundifolium can form hybrids with other species in the genus. In particular, Eupatorium godfreyanum is a hybrid of E. rotundifolium and Eupatorium sessilifolium.
Uses Eupatorium rotundifolium contains sesquiterpene lactones of the guaianolide type including euparotin acetate and eupachlorin acetate, both of which inhibit tumor growth in vitro when isolated from the plant.
Medicinally, the plant was used to treat intermittent fevers in the past.
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