Since the pre-Hispanic period, Xochimilco's economy has traditionally been based on agriculture, mostly by supplying to the needs of Mexico City. This not only dominated the economy but also the area's religious practices, some of which can still be seen to the present day. Agriculture still remains important in the borough, but most of the focus has shifted to flowers and ornamental plants. One major reason for this is the poor quality of the area's water supply. Xochimilco has four major markets dedicated to the sale of plants and flowers: Cuemanco, Palacio de la Flor, Mercado de Madre Selva and the historic market at San Luis Tlaxialtemalco. Cuemanco is the largest in Xochimilco and the largest of its kind in Latin America, covering thirteen hectares, with its own cactus garden and forms part of the ecological preserve of Cuemanco. The borough produces 2.5 million poinsettias each year, accounting for most of the 3.5 million sold each year in Mexico City. This represents an income for the borough of about 25 to 30 million pesos annually, grown by about 10,000 growers.