Chinese cabbage has been cultivated for over six thousand years in China. ''Brassica rapa'' seeds have been found in jars in the excavated New Stone Age settlement of Banpo. They were a common part of the diet in southern China by the 5th century.
The Ming Dynasty pharmacologist Li Shizhen studied the Chinese cabbage for its medicinal qualities. Before this time the Chinese cabbage was largely confined to the Yangtze River Delta region. The Chinese cabbage as it is known today is very similar to a variant bred in Zhejiang around the 14th century. During the following centuries, it became popular in northern China and the northern harvest soon exceeded the southern one. Northern cabbages were exported along the to Zhejiang and as far south as Guangdong.
They were introduced to Korea, where it became the staple vegetable for making kimchi. In the early 20th century, it was taken to Japan by returning soldiers who had fought in China during the Russo-Japanese War. At present, the Chinese cabbage is quite commonly found in markets throughout the world.
There are two distinctly different groups of ''Brassica rapa'' used as leaf vegetables in China, and a wide range of varieties within these two groups. The binomial name ''B. campestris'' is also used.
This group is the more common of the two, especially outside Asia; names such as ''da baicai'' ; ''Baguio pechay or pechay wombok'' ; ''Chinese white cabbage''; ''baechu'' , ''wongbok, nappa, or napa cabbage''; and ''hakusai'' usually refer to members of this group. ''Pekinensis'' cabbages have broad green leaves with white s, tightly wrapped in a cylindrical formation and usually, but not necessarily, forming a compact head. As the group name indicates, this is particularly popular in northern China around Beijing .
This group was originally classified as its own species under the name ''B. chinensis'' by . When used in English, the name ''bok choy'' typically refers to ''Chinensis''. Smaller in size, the Mandarin term ''xiao baicai'' as well as the descriptive English names ''Chinese chard'', ''Chinese mustard'', ''celery mustard'', and ''spoon cabbage'' are also employed. ''Chinensis'' varieties do not form heads; instead, they have smooth, dark green leaf blades forming a cluster reminiscent of or celery. ''Chinensis'' varieties are popular in southern China and Southeast Asia. Being winter-hardy, they are increasingly grown in Northern Europe.
Commercial variants of ''Chinensis'' include:
*''Bok Choy'' ; succulent, white stems with dark green leaves and ''Baby Bok Choy''; succulent, pale green stems with leaves the same color; both quite common in US West Coast oriental markets.
*''Choy Sum'' : also called ''yu cai'' , this brassica refers to a small, delicate version of pak choi. In appearance it is more similar to rapini or broccoli rabe, than the typical ''pak choi''. In English, it can also be called "Flowering Chinese Cabbbage" due to the yellow flowers that comes with this particular vegetable. "Choy sum" is sometimes used to describe the stem of any Chinese cabbage or the heart of ''Shanghai pak choi''.
*''Shanghai Pak Choi'' refers to dark green varieties where the varioles are also green. It is probably the most common vegetable in Shanghai, where it is simply called ''qingcai'' or ''qingjiangcai'' .
In Mandarin Chinese ''bai cai'' refers to both groups of ''B. rapa''. However, the English word ''bok choy'' and its variations ''bok choi'' and ''pak choi'' are derived from the cognate, which instead denotes one specific variety of cabbage, namely those with white stems and dark green leaves. The other varieties all have different names which entered the English language as ''you choy'', ''choy sum'', ''napa'' and ''baby bok choy'', etc. Hence the English word ''bok choy'' is not equivalent to the Mandarin word ''bai cai'', though the Chinese characters are the same.