"Unordered" Versus "Ordered" Characters

Multistate morphological characters have generally been treated as either “unordered” or “ordered” in phylogenetic analyses using parsimony. Because ordering relations do not apply to the states of characters treated under these methods, I prefer “maximally connected” character to “unordered” character and “minimally connected” character to “ordered” character. This paper formally defines the two character types, compares their properties, and considers the consequences of the two methods for both resolution and congruence. The results demonstrate that minimally connected characters increase resolution relative to maximally connected characters. Minimally connected characters do not, however, necessarily increase congruence among data sets. Because both methods produce nonrandom congruence among data sets, both character types constitute valid phylogenetic methods. A mixed-parsimony approach is advocated, wherein multistate characters are treated as minimally connected whenever reasonable but treated as maximally connected otherwise.