Tomatillos are native to Mexico and Central America, where they were cultivated by the Aztecs as early as 800 BC, and they remain a staple of Mexican cuisine today. In Mexico, they are sometimes referred to as tomate verde (green tomato), or tomatillo, which just means small tomato. These fruits are considered ripe once the papery calyx that encloses each fruit has dried and turned from green to light brown, but the fruit itself does not become sweet like a tomato. Even when the fruit is fully ripe, and turns an appealing yellow, it remains somewhat tart. It is the tart, slightly acidic nature of the fruit that makes it perfect for processing (raw or cooked) into salsas, notably salsa verde, and even jam. Diced raw tomatillo also adds a pleasing crunchiness to guacamole.