Curry leaves lend a lingering aroma to the dish, and are discarded before serving. They come from the curry plant, a shrub native to India and Sri Lanka. They are slender, dark green and similar to a small, narrow bay leaf.
The leaves smell fresh and pleasant, remotely reminiscent of tangerines, and add an aromatic curry flavour to any dish. They are the trademark of southern Indian cooking, used to flavour meat, fish, vegetables, lentils, rice and bread. They are also used in preparing Madras curry powders.
If you cannot get hold of fresh curry leaves, try the dried variety. You can buy either from Asian shops.