Kaffir lime, or or Citrus hystrix, is also known as Indonesian lime, wild lime or by its Thai name – makrut lime. Both the rind of the fruit and the leaves are used. The fruit is a dark lime green in color and looks like a pear with the outer rind being knobby and wrinkled. The juice of the fruit is sour and rarely used. The grated rind is added to curry pastes, fish cakes and larb (a type of minced meat salad). Kaffir Lime Leaves are a signature flavor of many Thai curries, salads, soups and stir-fries.
Kaffir Lime leaves have a shiny appearance and these leathery leaves grow together in an unusual attached form (looking like they are attached at the stem). Similar to bay leaves, whole Kaffir leaves are generally removed from the dish prior to serving. If you are going to leave them in a dish you should shred them very, very thin or grind them. They do retain their flavor when cooked so it is okay to add these early in the cooking process. But be careful with these, as the longer they are in a dish the more flavor they provide.