Ambrosia polystachya

Resembling no. 4 [Ambrosia artemisiifolia L.], but a colonial perennial from creeping roots; lvs thicker, short-petiolate or subsessile, usually only once pinnatifid, averaging narrower in outline; fruiting invol merely tuberculate above, sometimes obscurely so; 2n=36, 72, 108, 144. Waste places, usually in dry or sandy soil; Mich. and Ill. to La., w. to the Rocky Mts., and casually intr. eastward. (July) Aug.-Oct. (A. coronopifolia)

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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