The tomatillo (Physalis philadelphica) is a plant of the nightshade family, related to the cape gooseberry, bearing small, spherical and green or green-purple fruit of the same name. Tomatillos, referred to as green tomato (Spanish: tomate verde) in Mexico, are a staple in Mexican cuisine. Tomatillos are grown as annuals throughout the Western Hemisphere. Often self-incompatible, tomatillos need a second plant to enhance pollination and guarantee fruit set.
The tomatillo fruit is surrounded by an inedible, paper-like husk formed from the calyx. As the fruit matures, it fills the husk and can split it open by harvest. The husk turns brown, and the fruit can be any of a number of colors when ripe, including yellow, red, green, or even purple. Tomatillos are the key ingredient in fresh and cooked Latin American green sauces. The freshness and greenness of the husk are quality criteria. Fruit should be firm and bright green, as the green colour and tart flavour are the main culinary contributions of the fruit. Purple and red-ripening cultivars often have a slight sweetness, unlike the green- and yellow-ripening cultivars, and are therefore somewhat more suitable for fruit-like uses like jams and preserves. Like their close relatives cape gooseberries, tomatillos have a high pectin content.
Tomatillo plants are highly self-incompatible (two or more plants are needed for proper pollination; thus isolated tomatillo plants rarely set fruit).
Ripe tomatillos will keep in the refrigerator for about two weeks. They will keep even longer if the husks are removed and the fruits are placed in sealed plastic bags stored in the refrigerator. They may also be frozen whole or sliced.