Glossary of "Cladistics (2nd ed.)" by Kitching et al. (1998)
- An artificial outgroup taxon in which each character is coded with the putative plesiomorphic state as estimated by an a priori method of polarization. See also all-zero outgroup.
- Kitching, I. J., Forey, P. L. Humphries, C. J. & Williams, D. M. 1998. Cladistics, 2nd ed.: the Theory and Practice of Parsimony Analysis. -xii + 228 pp. Oxford University Press, New York.