Persicaria maculosa
A plant of streams and low, wet areas. Listed in older books as Polygonum persicaria. I haven't seen it in Indiana, so my pictures are from New Mexico.
Plant habit near the Gila River south of the Gila Cliff Dwellings, New Mexico, 7/11/05.
Foliage & inflorescences near the Gila River, 7/11/05.
An inflorescence near the Gila River, 7/11/05.