One of the most important flavorings in Thai cooking, this herb has long, thin, gray-green leaves and a scallionlike base. Citral, an essential oil also found in lemon peel, gives lemon grass its sour-lemon flavor and fragrance. Lemon grass is available fresh or dried in Asian (particularly Thai) markets. It’s used to make tea and to flavor soups and other dishes. Lemon grass is also called citronella and sereh.