Considered a native American plant, but not collected in Michigan before 1861 or after 1939. During that 80-year period, recorded from farmyards, roadsides, and disturbed places.

Other species have frequently been misidentified as this one. The knotweeds are often troublesome to determine, as any of the characters cited is open to exception and one must too often make a judgment on a balance of characters. The leaves of P. erectum may be similar to the shapes in P. aviculare, but run distinctly larger. Mature plants are rather strongly heterophyllous, with flowers (fruits) in axils of much-reduced leaves or bracts.