| Choy sum (Cantonese) Cai xin (Mandarin) | |
| Species: | Brassica rapa var. parachinensis |
| Group: | Chinensis, Pekinensis groups |
| Origin: | China, before the 15th century |
| Subdivision: | Many; see text. |
Choy sum (also spelled choi sum, choi sam in Cantonese; cai xin, caixin in Standard Mandarin) is a leafy vegetable commonly used in Chinese cuisine. It is a member of the genus Brassica of the mustard family, Brassicaceae (Brassica rapa var. parachinensis or Brassica chinensis var. parachinensis). Choy sum is a transliteration of the Cantonese name, which can be literally translated as "heart of the vegetable". Choy sum is also called yu choy (you cai in Standard Mandarin; Chinese: 油菜). It is also known as Chinese flowering cabbage.[1]
Choy sum is a green leafy vegetable similar to gai lan, and can be characterized by the distinct yellow flowers which it bears. Each flower has four yellow, oval to round petals with six stamens on fleshy, erect stems which are 0.5to in diameter and 15to tall with light to dark green, and are oval (becomes acuminate shaped, or basal-shaped near the flowering stage) with slightly serrated margins leaves, which never forms compact heads like the cabbage. Fruits can develop out of cross-pollination or self-pollination, and are silique structured, that open at maturity through dehiscence or drying to bare open to brown or black seeds that are small and round in shape. A single pod can bear 4 to 46 seeds.
The height of the plant varies greatly, ranging from 10to depending on the growing conditions and the variety. Flowering usually appears when there are about 7 to 8 leaves on the plant or about 20frac=2NaNfrac=2 tall. The bulk of the root system is found within a depth of 12frac=2NaNfrac=2 and is confined to a radius of 12frac=2NaNfrac=2.[2] [3]
The whole plant is overall an annual, herbaceous plant, rarely perennial, rarely growing into subshrubs. The whole plant consists of a simple or branched (when it is near the flowering stage), leafy structure. It grows best in soil with a minimum pH level of 5.6, maximum pH level of 7.5.[4]