Bidens tripartita L.
Family: Asteraceae
straw-stem beggar-ticks, swamp marigold, swamp tickseed
Bidens tripartita image
Emmet J. Judziewicz  
Etymology: Bidens: derived from Latin bis, "twice," and dens, "tooth," hence meaning "2-toothed" and referring to the bristles on the achenes
Plants: erect, annual, 4"-80" tall, mostly smooth forb with straw-colored stems
Leaves: mostly stalkless, usually toothed, simple but with 1-4 lobes near the base
Flowers: head with or without 1 1/2" rays, pale yellow to greenish disk 1/3"-3/4" wide, leafy bracts usually longer than the disk; inflorescence of a few stalked, erect heads; blooms Aug.-Oct.
Fruits: usually with 3 barbed awns (the center one shortest), smooth except for the edges of the barbs, very flat fruit drawing
Habitat: moist to wet; disturbed areas