A new species of Macrosiphum is described from southern Mexico City, Mexico based on apterous and alate viviparous females and alate males. Macrosiphum tonantzin, n. sp., was found living year-round on Pittosporum undulatum (Pittosporaceae), a plant native to Australia and grown in Mexico as an ornamental. Relationships of this species to other Macrosiphum are discussed, as well as hypotheses about its possible geographic origin and life cycle.