I feel about bok choy as Supreme Court Justice Potter Stewart did about obscenity. It is hard to define, but I know it when I see it. More serious foragers in Chinese markets allow themselves to get bogged down in the not insignificant differences separating bok choy or pak choi from Canton, Shanghai, Taiwan (or Fengshan); choy sum, tatsoi, and yau choy, in their seedling, baby, mature, and flowering varieties, not to mention white-stemmed, dwarf-stemmed, and green-stemmed forms, some of which are different stages or different names for each other. The scientific name is even less help, especially when dealing with Chinese greengrocers, who know no more than you do about the fine taxonomic nuances of Brassica rapa, Chinensis group. Nor does it reduce the nomenclatural turbidity to know that the English vernacular names for this group of Brassica—among them Chinese cabbage, Chinese celery cabbage, Chinese white cabbage—may easily be confused with that other Chinese cabbage of the same species, B. rapa, Pekinensis group, the cabbagey white, leafy plant also known as Napa, da bai cai, wong bok, and—horribile dictu—bok choy. Then there is the matter of Chinese broccoli or kale, B. oleracea, Alboglabra group, which I am going to ignore in order to achieve what St. Paul called the peace “which passeth all understanding.”*
Suffice it to say that in the real world of vegetable markets in the West, it is almost impossible to confuse the two great groups of Chinese cabbages. The large stalkless white cabbagey types are Pekinensis and will be sold either as Napa or simply Chinese cabbage. The green-leafed plants with the stalks are the Chinensis group, and almost anyone, even a botanist, is likely to call them “bok choy” when speaking English. For my taste, the type that most merits a trip to Chinatown is any small bok choy variety with the tiny flowers. Tender and succulent, this variety, like all the others of its group, is normally stir-fried. The cook triumphs over Nature in all her perplexing diversity.