What is this plant?

[brandonsdad02]

I got this from a friend of mine this spring and put it in my stream.. Grew really well and took off like mad. Very invasive and sends out vines that root and grow up. Got very big and has purplish flowers on it. Has been hard to control and I've been yanking it out all summer.

This is what it started out as this spring.

 

[Waterbug]

Pic of flower would help. My guesses would be a mint like Mentha longifolia, but there are many kinds it could be. Peppermint, water mint, spear mint, etc. You can tell by crushing a leaf to test if it's aromatic.

Maybe one of the Joe Pye Weeds like hardy ageratum.

 

[addy1]

Looks like marsh betony, I have it also, grows like crazy, easy to yank out and control. Shallow runners, in my bog.

 

[taherrmann4]

agree with addy, marsh betony. Mine started growing over my bog wall and into my landscaping.

 

[addy1]

I have found all of the plants that like the bog can very easily become "invasive" they grow like crazy. I just go out and do the old yank and toss.
Even the day lilies have gone insane, next spring they are being thinned from the bog and heading out to dirt planting in the yard.

Can't complain, the pond is kept perfect by the bog and the plants that grow in it.