Choy sum is a cultivar of Brassica rapa, a species of vegetable that includes a wide range of subspecies including turnips, bok choy, and napa cabbage. Choy sum is a leafy green also know as Chinese flowering cabbage. It is eaten widely around the world. The shoots and young leaves can be stir-fried, boiled, or steamed, and contain Vitamin A, calcium, potassium, and folic acid. Growing conditions are very similar to mustand green. Harvested 30 to 50 days after sowing. 

Mae Tha

Productive, large-leaf variety from Green Net in Mae Tha, Thailand.

Burmese

Smaller leaves. From the Irrawaddy Delta region of Myanmar.