Cladistics for the Practicing Taxonomist-An Eclectic View

Abstract

An outline of the use of character compatibility analysis as an aid in taxonomic studies is given through a summary of phenetic and cladistic analyses of the Ranunculus hispidus complex. These results form a basis for discussing cladograms as an aid in the formulation of a classification. Simpson's concept of consistency is more desirable for analyzing a cladogram and its correspondence to a classification than is the sister group criterion of Hennig. Any classification is consistent (in Simpson's sense) with what is known about phylogeny if all the classes in the classification are convex. Convex, as applied to fully resolved cladograms, is operationally defined. Several examples, including studies of the Ranunculus hispidus complex, demonstrate the nature of convex groups, traditional classification, and cladograms. The use of the more flexible consistency criterion with an eclectic view of classification in which numerous lines of evidence can be helpful in understanding the taxonomic and evolutionary relationships of organisms is advocated. Placing classificatory results in an evolutionary context is one of the primary interpretive activities of the practicing systematist. One means by which these interpretations are expressed is in branching diagrams or cladograms that describe the sequence and direction of evolutionary change that could have occurred in a set of characters. Cladistics comprises idealized concepts by which such reconstructions are achieved and operational interpretations are developed as data analytic procedures. Although botanical systematists induce evolutionary relationships as part of their taxonomic studies, few are familiar with the field of cladistics and the way in which cladistic methods may be used as an aid in this regard. I will address from the view of a user of cladistic methods two issues. First, by means of a brief discussion of the results of phenetic and cladistic analyses of the Ranunculus hispidus complex, I will indicate how cladistic analyses have been a useful tool in taxonomic studies of this group, and in particular how character compatibility analysis has enabled a more explicit and repeatable analysis to be conducted. Second, and more fundamental to taxonomists, I will discuss the role of cladistic analysis in taxonomic decisions and in the construction of classifications. CHARACTER COMPATIBILITY ANALYSIS Cladistic methods involve analysis of the changes in the states of sets of characters for groups of organisms, most frequently contemporaneous organisms. This analysis can be accomplished in several ways. Two general classes of methods, parsimony analysis and character compatibility