I'm in z 6 (Boston MA). I found this plant and at first thought it's Pontederia cordata (Pickerel weed). The blooms look very similar but 3/4 in. Leaves look more like mint's - narrow, toothed but chartreuse colored. It has 3-4 stems about 10in and are reddish -mistard like colored. I guess it should be smth wild/native. Thank you!