Indian hemp is a spreading upright perennial that often grows streamside or in moist depressions. It grows in the mud and cobble along the Clark Fork, but occasionally you'll find it in much drier sites. It resembles milkweed (although it isn't), and like milkweeds it offers valuable resources for the caterpillars of certain pollinators. 
 
 
 
Indian hemp is named after the tough fibers that native peoples used to make ropes, nets, and the like, and is poisonous if ingested (do not ingest!). This plant can be aggressive in small spaces, so plant it where it has space to roam a bit, or plant it with other agressive sun and water lovers, and let them duke it out (that's what I do, anyway). Canada goldenrod, showy milkweed, and fireweed are good options. 
 
 
 
Image: By Fritzflohrreynolds - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31373979