Perilla (aka Japanese Basil, Beefsteak Plant, Shiso)
I found an expected resident growing vigorously next to my zuccini plants, and eventually tracked it down as Perilla, also known as Beefsteak Plant (I have no idea why), Japanese Basil (which is plausible), and Shiso. It's native to Asia, used in cooking and herbal medicine, and oil can be pressed from the seeds "for use in paint, dyes, and inks". The leaves, when crushed, smell something like sesame oil (in my opinion).
Does anyone have experience with this plant to share?