I believe this is a native plant here in Indiana. I really like it and it does not appear to be invasive. Kept a small bit when constructing the pond but, recently found a large patch of this plant in another area that I'm going to transplant from. It has directly opposing leaves like a honey suckle and it produces quarter size yellow flowers in the spring. Seems to thrive as much out of water as it does in water. Anyone have a clue what it is?