2a. var. ambrosioides

Spikes with leaflike bracts 0.3–2.5 cm long at most of the nodes. Calyx lobes rounded to very slightly keeled dorsally. July–November.

Introduced, scattered nearly throughout the state, but more common south of the Missouri River (native of tropical America; naturalized widely in the U.S. and Canada). Banks of rivers; also crop fields, fallow fields, gardens, roadsides, railroads, and open, disturbed areas.