I guess that rules out that idea! It's the only thing I could come up with, and if you hadn't posted the pictures, it would have slipped right by me. I guess it will remain a mystery as to how it made its way to my house!
It's in almost full shade, behind a hosta, and under the window AC, so I'll see what happens. I am so tempted to pull it, but I really want to see if it blooms. It just needs to survive to do that. Guess I better learn how to take care of it until then!
Thanks so much to all of you for your help! I truly appreciate it!