Sorry about the offensive title - I didn't name this plant. Kaffir (or wild) lime is a wonderful fruit with spice application.
Kaffir lime tree in full leaf
Ripening kaffir lime fruits
Ripe kaffir lime fruits
Kaffir leaves are native to almost the whole of South-East Asia.
The leaves, which have a characteristic shape due to their winged petioles that resemble leaves themselves. The fruits, especially the skin, may also be used.
Rutaceae (citrus family). Within the genus citrus, kaffir lime belongs to subgenus papeda and is less closely related to those species yielding the popular citrus fruits.
Strongly lemon-like. Although many people judge the fragrance to be crude, dominating and penetrating on first contact, most find it uniquely refreshing after having grown accustomed to it.
The word "kaffir" in English and other European languages is used as an offensive term for black people, having been historically applied by white Dutch settlers to the Xhosa people indigenous to South Africa. It comes from Arabic kaffir "infidel" or "non-Muslim" via obsolete Spanish and Portuguese cafre "barbarian". The ultimate source is a Semitic root kpr "village", with a derogatory connotation of backwardness. The meaning "infidel" arose from an implication of retarded or incomplete Islamisation in remote villages. Distantly related is Turkish gâvur "infidel", which was loaned to Old English as giaour. The German term kaff (derogatory for "remote place" or "small village") might have Yiddish sources, although others derive it from Romany gāw "village".
The species name hystrix from the Greek hystrix "porcupine" refers to the many thorns of the plant. The Latin species name citrus "citron tree" has a similar derivation to the Greek kedros "cedar".
Several European names refer to the plant's origins in South-East Asia, e.g. English "Indonesian lime leaf", Dutch Indonesische citroenboom and German Indonesische zitronenblätter.
Kaffir lime leaves are a very popular spice in Thailand, their characteristic flavour appearing in soups, stir-fries and curries. In Thai cuisine, kaffir lime is frequently combined with garlic, greater galangale, ginger, fingerroot and liberal amount of chillies. Fresh Thai basil is needed for the authentic fragrance.
A dish most popular in Thailand and among foreigners is tom yam, a fiery-hot, sour and very aromatic soup. Tom yam gung is prepared from shrimps, tom yam gai from chicken and tom yam pla from fish. The soup is flavoured with chillies, lime juice, fish sauce, greater galangale, lemon grass and kaffir lime leaves. It is served topped with aromatic greens, usually horapha "basil" or coriander. A related soup is tom khaa, which contains more greater galangale and is less spicy due to a splash of coconut milk added. Similar soups are prepared in other South-East Asian countries.
Kaffir lime leaves are popular in the West of Cambodia, but less so in Vietnam. Malay and Indonesian (especially, Balinese) cuisines use them sporadically for chicken and fish. Kaffir lime has a very strong, characteristic fragrance that cannot easily be substituted by other spices (lemon myrtle leaves or lime peel are probably the best substitute). Dried leaves lose their flavour within a year and are therefore best kept frozen. The fruit juice, which is very sour and has the same fragrance as the leaves, is sometimes added to fish or poultry dishes in Malaysia and Thailand and is less commonly used in Indonesia.