Thank you both.
Yes, Mike. I call it Pilea. It's also known here as artillery plant because the seeds are so plentiful and extremely tiny that it looks like gunpowder has been dropping from the plant. When it first showed up in my greenhouse (I don't know from where), I thought it was very beautiful; so, I let it be. BIG MISTAKE! This stuff volunteers everywhere and I have to constantly pull it out of seedling compots etc., or else it will overwhelm the plants.
I noticed in my local Garden Centre last week that they have 2.5" pots of this manace for sale at $3.99 each! Yikes! I've been killing thousands of dollars worth of the stuff, each month! But, I bet there isn't a local market for hundreds of pots of it. *sigh*