The tomatillo (Physalis philadelphica), also known as the Mexican husk tomato, is a plant of the nightshade family bearing small, spherical and green or green-purple fruit of the same name.istory [edit]. Tomatillos were domesticated in Mexico before the coming of Europeans, and played an important part in the culture of the Maya and the Aztecs, more important than the tomato. The specific name philadelphica dates from the 18th century.