pak choi (Chinese: 白菜; Brassica rapa subsp. chinensis)
Bok choy is a type of Chinese cabbage. Chinensis varieties do not form heads; instead, they have smooth, dark green leaf blades forming a cluster reminiscent of mustard or celery. Chinensis varieties are popular in southern China and Southeast Asia. Being winter-hardy, they are increasingly grown in Northern Europe. This group was originally classified as its own species under the name Brassica chinensis by Linnaeus.