Brassica rapa
Tatsoi ("Brassica rapa subsp. narinosa" or "Brassica rapa var. rosularis") is an Asian variety of "Brassica rapa" grown for greens. Also called tat choy, it is closely related to the more familiar Bok Choy. This plant has become popular in North American cuisine as well, and is now grown throughout the world.