The peppery leaves of the mustard plant are a rich dark green and have a pungent mustard flavor. They belong to the same family of vegetables as collard greens, broccoli, Brussels sprouts, kale and kohlrabi. A popular "soul food" ingredient. These oval-shaped leaves with frilled or scalloped edges have a sharp, nippy taste. Young, tender leaves can be added to salads, providing a radishy “bite” along with its attractive appearance. They benefit from slow cooking which creates a mellow flavor; or blanch them and add to soups, creamy purees or sautes. Select small leaves for salads; any size for cooking since tenderness doesn’t depend on size when cooked. 

 
Look for crisp young leaves with a rich green color. Reject those with yellow or pitted leaves or thick, fibrous stems. Refrigerate greens in a plastic bag for up to a week. 

Rinse leaves in cool water to remove sand and dirt. Strip off stems and discard. Boil or steam. Add to soups. Saute with other cooked greens. 

Mustard Greens are available year-round. They are low in fat and cholesterol free. They are also very low in sodium and calories and high in folate and vitamins A and C, good source of calcium and loaded with anti-oxidants.


Here is a great site for all greens:
http://internet.epicurean.com/latest/current/greens/leaves.html

http://www.agr.state.nc.us/markets/commodit/horticul/leafy/

http://www1.epicurious.com/e_eating/e02_wintering/winterveges/greens.html