An Asian vegetable and green related to the Pak Choy family of cabbage plants, that is often considered to be the flowering version of this vegetable green. Also referred to as Bok Choy Sum, this plant has small yellow flowers that bloom on long fleshy white or green stalks topped with dark green oval-shaped leaves.
Choy Sum is grown for its thick-stemmed shoots and flower tips that are crisp and flavorful. It is often served in salads, Asian soups or stir-fried dishes containing meat and vegetables, providing a crisp textured vegetable with a delicate, slightly mustard-like flavor. It has a similar appearance and may be confused with broccoli raab however, it provides a milder and sweeter flavor.
To prepare, wash the greens thorougly and then trim a small amount from the bottom of the stalks. The stalks can be served cooked until wilted but retain the crunchy texture. The greens can be prepared by boiling, steaming or stir-frying. If blanched to eat as a vegetable, choy sum can be served at room temperature and dressed lightly with soy sauce or a sesame oil. To store, place the greens in a plastic bag and refrigerate.
Source: http://www.recipetips.com/glossary-term/t--36228/choy-sum.asp
