The lime is a small, round, intensely green citrus fruit, prized for a juice that is sharper, more aromatic and more bitter than lemon. Thin-skinned and seedy, it carries a high-toned, almost piney perfume in its oil-rich peel. From the daiquiri and the margarita to ceviche, Thai curries and key lime pie, it is one of the kitchen's essential sources of bright, fragrant acidity.