Brassica rapa chinensis
This species has been cultivated as a food crop for many hundreds of years and, in that time, several quite distinct forms have arisen. The nomenclature of these forms is confused, to say the least, and by no means universally accepted. We have followed the treatment used by GRIN, though it is very likely to be revised in the future[
Brassica campestris chinensis (L.) Makino
Brassica chinensis L.
Brassica chinensis utilis M.Tsen & S.H.Lee
Brassica dubiosa L.H.Bailey
Brassica napus chinensis (L.) Schulz.
Brassica oleracea chinensis (L.) Prain
Brassica rapa amplexicaulis Y.Tanaka & Ono
Brassica rapa chinensis (L.) Kitam.
Brassica rapa rosularis M.Tsen & S.H.Lee
Raphanus chinensis (L.) Crantz
Common Name: Pak Choi
Pak choi is a biennial plant developed in cultivation from Brassica rapa. Growing from a taproot that is not fleshy, it forms an open head of twenty or more leaves from a basal rosette. The leaves have thick, fleshy petioles. The plant grows 20 - 40cm tall, eventually producing a flowering stem up to 100cm tall.
The plant is widely cultivated in both temperate and tropical areas, but especially in China, for its edible leaves[
The oil contained in the seed of some varieties of this species can be rich in erucic acid which is toxic. However, modern cultivars have been selected which are almost free of erucic acid.
A cultivar of garden origin
Not known in the wild
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Pak choi arose through cultivation in the warm temperate zone and can also be cultivated in the tropics and subtropics . It grows best in areas where annual daytime temperatures are within the range 20 - 25°c, but can tolerate 10 - 32°c[
]. Plants are not tremendously winter-hardy, though they will withstand light frosts[
]. It prefers a mean annual rainfall in the range 900 - 1,400mm, but tolerates 300 - 2,000mm[
Succeeds in full sun in a well-drained fertile preferably alkaline soil[
]. Prefers a cool moist reasonably fertile soil[
]. Prefers a pH in the range 5.5 - 7, tolerating 4.3 to 7.5[
]. The plant is shallow rooted and intolerant of drought, it needs to be grown in a moist fertile soil for the best quality leaves[
A fast-growing plant, there are many named varieties and some can be ready in as little as five weeks from sowing the seed[
Forms with green stems tend to stand up better to adverse conditions than white-stemmed forms[
Yields may be 10 - 20 tonnes per hectare for small cultivars and 20 - 30 tonnes for large cultivars[
Leaves - raw or cooked[
]. They can be eaten at any stage from seedling to mature plant[
]. Well-flavoured, they are sweet with a hint of mustard[
].The leaves are also dried for winter use[
]. The leaves have pronounced stems and these can also be eaten, they tend to have a mild, almost bland flavour[
]. A nutritional analysis is available[
Immature flowering stems - cooked like broccoli[
]. A sweet flavour[
An edible oil is obtained from the seed[
The leaf is antiarthritic, antiscorbutic and resolvent[
Some forms of this plant are cultivated for their oil-rich seeds[
]. A semi-drying oil, it can be used as a lubricant, luminant, in soap making etc[
Seed - sow in situ May to August. Spring sown crops are prone to run quickly to seed if there is a spell of cold weather[
]. Some varieties can also be sown in a cold greenhouse in autumn or early spring to provide leaves overwinter and in late spring.