Thank you, Stewart and Nelly!
Nelly, the berries on this one aren't ripe yet, but I think
I had another one of these in another planter a while back,
and its flowers were black. So it may be a solanum negrum.
In any event, given the leaf and flower photos I've found,
I'm sure you're both correct that it's something in the
solanum family. (But not a tomato. I do know how to recognize