I have no idea what this is. It's a pretty good size - probably 14 to 18 inches tall now. At first we thought it might be a potato plant, but after looking them up online, it looks nothing like one. It's growing in the one of the beds of my garden (we did dump food scraps/compost in there over the winter, so it's pretty likely that it's a vegetable or fruit.) Any ideas? I'm pretty sure it's not a lettuce of any kind, but other than that, I don't know.
