~ Editing my original post to say the plant was identified as
Bitter Dock (Rumex obtusifolius)
I found another unknown plant popping up in a container on my deck. There is a lily of some sort (can't remember the name) growing in this pot and a few weeks ago I noticed something else sprouting in the container ... nothing I planted, so it's either a gift from the birds or was in the potting medium I used. I have no clue what it is so I thought I'd post a picture and see if anyone recognizes it. Probably a weed but it sure has pretty foliage: