Glossary of "Cladistics (2nd ed.)" by Kitching et al. (1998)
- A character in which the transformations in one direction cost the same number of steps as the transformations in the opposite direction. For example, in the undirected character, 0 <-> 1, the transformations 0 -> 1 and 1 -> 0 each cost the same number of steps. Wagner optimization and Fitch optimization use undirected characters. Cf. directed.
- 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.