This wetland plant took me a while to key out, since I had never seen it’s flowers.  Interestingly, I keyed it out using some guess-and-check with Google Image, and the next day I found some with flowers!  The first two images are from last year, and the rest are from this year.  There is a distinct change in leaf morphology once the plant has established, and to tell the two species apart in this genus, you must examine the relative density and size of the hairs covering the stems.