Chinese cabbage (Brassica rapa, subspecies pekinensis and chinensis) can refer to two distinct varieties of Chinese leaf vegetables used often in Chinese cuisine. These vegetables are both related to the Western cabbage, and are of the same species as the common turnip. Both have many variations in name, spelling, and scientific classification–especially the “bok choy” or chinensis variety.
Main article: Napa cabbage
This group is the more common of the two, especially outside Asia; names such as napa cabbage, da baicai (lit. “large white vegetable”); Baguio pechay or pechay wombok (Tagalog); Chinese white cabbage; baechu (Korean), wongbok and hakusai (Japanese: 白菜) usually refer to members of this group. Pekinensis cabbages have broad green leaves with white petioles, tightly wrapped in a cylindrical formation and usually forming a compact head. As the group name indicates, this is particularly popular in northern China around Beijing (Peking).
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 B. chinensis by Linnaeus.
Chinensis spelling and naming variations
Other than the ambiguous term “Chinese cabbage,” the most widely used name in Northern America for the chinensis variety is bok choy (from Cantonese, literally “white vegetable”; also spelled pak choi, bok choi, and pak choy). Less commonly, the Mandarin term xiao baicai (“small white vegetable”) as well as the descriptive English names Chinese chard, Chinese mustard, celery mustard, and spoon cabbage are also employed.
 Commercial variants of Chinensis
* Bok choy (Chinese: 白菜; literally "white vegetable"); succulent, white stems with dark green leaves. * Choy sum (Chinese: 菜心; pinyin: càixīn; literally "vegetable heart"; Hokkien chai sim), this brassica refers to a small, delicate version of bok choy. In appearance it is more similar to rapini or broccoli rabe, than the typical bok choy. In English, it can also be called "Flowering Chinese Cabbage" due to the yellow flowers that comes with this particular vegetable. The term "choy sum" is sometimes used to describe the stem of any Chinese cabbage, or the soft inner core of a bok choy with the tougher outer leaves removed. * Baby bok choy or Shanghai bok choy (Chinese: 上海白菜; pinyin: Shànghǎi báicài; Japanese: 青梗菜, chingensai) refers to greener varieties where the varioles are also green. It is simply a less-mature version that could develop into the white-stemmed variety with more time to grow before being harvested. In Shanghai and other eastern China provinces, it is simply called qingcai (青菜; literally blue/green vegetable) or qingjiangcai (青江菜; literally "blue/green river vegetable").