Tomatillo (Physalis ixocarpa) is known in Mexico as tomate verde (green tomato), tomate de cáscara (husk tomato), and miltomate, though it is not a tomato at all. In actuality it is related to the Cape gooseberry and American ground cherry. In all three of these the fruit (a small to medium-size berry) is encased in a thin, translucent paperlike outer skin that must be removed before cooking. According to Teresa Castellò Yturbide in Presencia de la Comida Prehispánica, tomatillo husks furnish a leavening agent when boiled in agua de tequesquite. The fruit is bright green, yellow-green, or sometimes purple, and can vary in size from a marble to a Ping-Pong ball.
