The species name rotundifolium is derived from the Latin "rotund" meaning "round" and "foli(um)" meaning "leaf." The genus name Eupatorium honors Mithridates VI of Pontus (132BC - 63BC), who was also known as Eupator Dionysius (Wikipedia contributors). Eupatorium rotundifolium contains eupatorin acetate, a guaianolide which may have anti-cancer properties, as well as eupachlorin acetate, a related compound which may also inhibit tumors (Wikipedia contributors).
There are five existing populations, but two of them have fewer than 10 plants. There is one other historical occurrence on Staten Island.
The larger populations seem stable, although one of them has not been revisited. There is no recent information on the smaller populations, so their trend is unknown.
There were only ever a couple of historical populations of this species and one of them was rediscovered. Five additional populations were subsequently discovered.
Some plants occur near phragmites that may eventually encroach on the plants. The populations along roads and power lines are threatened by succession if their open habitat is not maintained, or they are directly impacted by maintenance machines.
This species needs disturbance to reduce competition from woody plants, but too much direct disturbance to the plants will reduce the population. Its habitat could be disturbed in the non-growing season to open it up for seed germination and colonization, but direct disturbance should be prevented during the growing season. Any nearby exotic invasive species need to be controlled.
In New York, Serrate Round-leaf Boneset has been found growing in open, often moist, sandy ground along roadsides, powerline right-of-ways, and next to interdunal swales and wet depressions (NYNHP 2010). Moist, low ground, roadsides, sandy soils (FNA 2006). Woods, in dry or seldom wet soil (Gleason and Cronquist 1991).
This plant is currently known from Suffolk County on Long Island, with one historical collection from Staten Island and an unconfirmed report from Queens.
This herb grows throughout the Southeast from Florida to Texas, north to Southern Pennsylvania, and up through Long Island to Southern New England. It is rare only in New York and Pennsylvania.
Eupatorium rotundifolium var. ovatum is a perennial herb, 40 to 100+ cm tall. The stems grow singly from rhizomes, are sparsely branched distally, and have tiny hairs. The leaves are sessile or nearly so, mostly opposite (distal sometimes alternate, lateral buds dormant or producing 1 pair of leaves) 3 to 6.0 cm wide and 1 to 2 times as long . The leaf blades are 3-nerved, deltate to orbiculate and broadest near the middle, with wedge-shaped bases, pointed tips and serrate margins, and are hairy and dotted with glands. The infloresence is of discoid flowers only, arranged into corymbiform (flat or round-topped) heads of 5 florets each, the corollas are white and 3-4 mm long, and the calices form pappi of 30-40 bristles 4 to 4.5 mm long. There are 8-10 phyllaries (involucral bracts) in 2 to 3 rows, each 2 to 6 mm long with acute tips, and pubescent and gland-dotted on their outer (abaxial) sides.
Flowers or fruit with leaves and entire stems are needed for identification of this species.
Eupatorium pilosum has leaves 2 to 3 times as wide as long, often with purple leaf bases. Eupatorium rotundifolium var. rotundifolium has leaves 3-nerved from their bases with crenate margins and subtruncate to broadly cuneate bases (in contrast to E. rotundifolium var. ovatum's leaves, which are 3-nerved distally to their bases with serrate margins and broadly cuneate to cuneate bases). E. rotundifolium var. scabratum has narrower leaf blades (2 to 5 cm), broadest near the base.
The time of year you would expect to find Hairy Thoroughwort flowering and fruiting in New York.
Eupatorium pubescens Muhl. ex Willd.
This species is hybrid-derived and should not be treated as a variety. It is now treated as a full species.
Flora of North America Editorial Committee. 2006. Flora of North America North of Mexico. Vol. 21. Magnoliophyta: Asteridae, Part 8: Asteraceae, part 3. Oxford Univ. Press, New York. xxii + 616 pp.
Fernald, M.L. 1950. Gray's manual of botany. 8th edition. D. Van Nostrand, New York. 1632 pp.
Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.
Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.
New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.
New York Natural Heritage Program. 2020. New York Natural Heritage Program Databases. Albany, NY.
Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research http://www.fccdr.usf.edu/. University of South Florida http://www.usf.edu/]. New York Flora Association http://newyork.plantatlas.usf.edu/, Albany, New York
This guide was authored by: Stephen M. Young
Information for this guide was last updated on: September 6, 2012
Please cite this page as:
New York Natural Heritage Program. 2020. Online Conservation Guide for Eupatorium pubescens. Available from: https://guides.nynhp.org/serrate-round-leaf-boneset/. Accessed April 2, 2020.