G. E.  Schatz and Le Thomas, A., ?Annonaceae: a primitive dicot family with an ancient center in Africa-South America?, in Biological relationships between Africa and South America, P.  Goldblatt, Ed. New Haven: Yale University Press, 1993.

G. E.  Schatz, ?A new Xylopia (Annonaceae) from Panama?, NovonNovon, vol. 3, pp. 475-477, 1993.