T. F.  Stuessy and Crisci, J. V., ?Problems in the determination of evolutionary directionality of character state change for phylogenetic reconstruction (Chapter 5)?, in Cladistics: Perspectives on the reconstruction of evolutionary history, T.  Duncan and Stuessy, T., Eds. New York: Columbia University Press, 1984, pp. 71-87.

C. A.  Meacham and Duncan, T., ?The necessity of convex groups in bioliogical classifocation?, Systematic Botany, vol. 12, pp. 78-90, 1987.

T.  Duncan, ?Cladistics for the practising taxonomist - an eclectic view?, Systematic Botany, vol. 5, pp. 136-148, 1980.

T.  Duncan and Stuessy, T. F., Cladistic Theory and Methodology. New York: van Nostrand Reinhold Company, 1985, p. 399.

W.  Burger, McNeill, J., Niklas, K., Thompson, W., Thorne, R., Stuessy, T., Meacham, C., Wiley, E., and Duncan, T., ?Panel Discussion?, Systematic Botany, vol. 5, pp. 221-231, 1980.