This plant popped up as a volunteer. I'm certain it's something I've grown before, I just don't know what. (Could it be knautia?) Leaves are opposite, serated.
My guess is a type of Buddleia, aka Butterfly Bush, aka Buddleja davidii. Possibly a seedling? In the Database, one can see the square stems in this variety.
Name: Kurt Woodbridge , Va (Zone 7a) Jai guru deva om
, I did the same thing not long ago.
knew it looked familiar but could not place it
sprouted up in the middle of no where , far from my butterfly bushes
A pint can't hold a quart , If it is holding a pint it is doing the best that it can.
and it is written ,
if the evil spirit arms the tiger with claws , brahman provided wings for the dove.
(Could it be knautia?) Leaves are opposite, serated.
, I did the same thing not long ago. 
