This ancient herb (one of the five bitter herbs of the Jewish Passover festival) is a native of eastern Europe but now grows in other parts of Europe as well as the United States. Though it has spiky green leaves that can be used in salads, horseradish is grown mainly for its large, white, pungently spicy roots. Fresh horseradish is available in many supermarkets. Choose roots that are firm with no sign of blemishes or withering. Horseradish should be refrigerated, wrapped in a plastic bag, and peeled before using. It's most often grated and used in sauces or as a condiment with fish or meat. Bottled horseradish is available white (preserved in vinegar), and red (in beet juice). Also available is dried horseradish, which must be reconstituted before using. See also wasabi.