Bok choy is a type of Chinese cabbage. Chinensis varieties do not form heads and have green leaf blades with lighter bulbous bottoms instead, forming a cluster reminiscent of mustard greens.
Its Chinese name, "pak choi," translates to "white cabbage," probably because of its blanched centers, but there are green varieties too. The stalks are crisp and the leaves are smooth and tender with a flavor somewhere between cabbage and chard. Plants form an upright head, with outward flaring leaves, and it's white or green stalks look like smooth, non-stringy celery. The stalk can shoot up to twice the size of the plant. Flower stalks grow from the center of the plant and have the yellow, 4-petal cross typical of the cruciferous family.