Eupatorium semiserratum DC.
Family - Asteraceae
Stem - Erect, to 1.2 m, moderatly to densely short-hairy, not hollow.
Stem and node.
Leaves - Mostly opposite, +/- sessile, often twisted to appear erect. Blades to 8 cm, oblanceolate to elliptic, tapered at base, blunt at tip, margins irregularly toothed, surfaces short-hairy and gland dotted. Lateral veins branching from midvein 2-12 mm from base of leaf. Axillary fascicles sometimes present at some nodes.
Inflorescence - Terminal panicles, +/- flat-topped.
Involucres - Narrowly cup-shaped, 2.5-4.0 mm. Bracts densely short-hairy, green.
Florets - Disk florets 5 per head. Corollas 2.5-3.5 mm long, white, sometimes glandular.
Flowering - August - October.
Habitat - Forest margins, swamps, old fields.
Origin - Native to the U.S.
Other info. - Despite its weedy appearance, this plant is uncommon in Missouri and represents an unusual and notable find. Its range in the state is restricted to the bootheel region.
Photographs taken at Otter Slough Conservation Area, Stoddard County, MO, 8-13-2015 (SRTurner).