Perilla frutescens. There's a green-leaved version as well. It's used as an herb. It imparts a clove/anise flavor, with the green having less anise and more clove-like flavor. It's used extensively in Japanese cooking. It's actually naturalized here (as in: East TN), could easily become invasive. If you let it go to seed, you * will* have more than you want, lol.

Common names include beefsteak plant, shiso, and many more.

Oh, and something I didn't know until recently, it's poisonous to herbivores (cattle, horses) when dried. They won't eat it fresh, but have been poisoned by eating it dried where it has infested fields harvested for hay. It is NOT poisonous to humans, and has been used in Asian medicine and cooking for centuries.

If you wish to research this plant use the scientific name, Perilla frutescens, because there is another plant, Iresine herbstii, which also goes by Beefsteak Plant.