1. Leaf bases (except sometimes the uppermost) connate around the stem.
1. Leaf bases entirely free and separate from the stem.
2. Leaves with distinct petioles; florets 8–50 (or more) per head.
2. Leaves sessile or nearly so (at most tapering to a narrow, winged base); florets fewer than 8 (usually 5) per head.
3. Stem densely puberulent on middle internodes; leaves tapered to narrow base (or short-winged petiole), with 3 prominent longitudinal veins (at least on basal half).
3. Stem glabrous on middle internodes (or sparsely puberulent); leaves truncate to broadly rounded at the base, with only 1 long vein (the midrib) prominent beneath.
All species found in Eupatorium
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. July 20, 2017. http://michiganflora.net/genus.aspx?id=Eupatorium.