Brassica rapa var. pekinensis, B. rapa. var. chinensis
Other names: Taiwan Bok Choi, Kwai Tsai, Kuai Choi, Kuai Cai, Baby Napa, Baby Chinese cabbage, Napa, Nappa, Wa Wa Tsai, Wa Wa Cai. *pak=bok, boc, pac, bai, bac, bak, pe. *choy=choi, tsai, tsoi, cai.
In North America, Taiwan Pak Choy is a special group of Chinese cabbage, distinguished by fast growing, early maturity and hairless leaves. They are mainly bunched for sale after harvested.
Taiwan Pak Choy has two types. Classical type (Brassica rapa var. chinensis) is a non-heading Chinese cabbage, such as Dynasty. Another new type is Kuai Cai (B. rapa var. pekinensis). Kuai Cai means "fast-growing Chinese cabbage" in China. It can be harvested in bunches at 25~35 days, which is similar to classical Taiwan Pak Choy. If planted with more space, It can be harvested later when a small head is developed. Therefore some growers call it Wa Wa Tsai in North America. If the weather allows it, It can grow into normal Chinese cabbage. Qingdao Express F1 and other QD series belong to this type.