My grandmother brought me a bunch of shade-loving plants from her garden to help me fill in a few gaps in my own. She had most of them identified but this one had her stumped. Here's what I know from her:
This is a perennial that thrives in shady conditions. It grows about 5 foot tall and produces small, but very fragrant, white blossoms in July or August. It spreads easily without human intervention. It was found in New York and may be a native species, but that is not guaranteed.