Origin and philosophy of the groundplan-divergence method of cladistics [Taxonomy, botany]

• Published in: Systematic botany 1980-04, Vol.5 (2), p.173-193
• Main Author: Wagner, W. H.
• Format: Article
• Language: English
• Subjects: Biological taxonomies; Cladistics; Divergent evolution; Evolution; Evolutionary genetics; Ferns; Hybridity; Phylogenetics; Plants; Taxa
• ISSN: 0363-6445; 1548-2324
• DOI: 10.2307/2418624

The Groundplan-divergence Method of constructing phylogenetic trees was created during the 1950's for illustrating systematic principles, but it was taken up widely by researchers carrying out monographic research. Based upon a study of certain Hawaiian ferns, the method attempts to deduce pathways of genetic change on the basis of phenetic evidence. It tries to estimate the amounts (grades), directions (clades), and sequences (steps) of phylogenetic divergence, using the concept of generalized or groundplan characteristics as the basis of judging primitiveness. Groundplan-divergence analysis is concerned with pathways of actual biological changes rather than with their chronology (when the changes took place) or their geography (where they took place). Obvious parallelisms, reticulations, and co-existences of ancestors and derivatives are accepted and embodied in the cladistics. The method involves the interplay of phenetic classification, the detection of taxa of hybrid origin, analysis of character trends, synthesis of generalized character states, estimation of divergence levels, grouping according to divergence formulas, and the connecting of lines with hybrid reticulations. The method is not able to overcome problems that are caused by such factors as major gaps in the phylogenetic record, important missing characters, excessive hybridization, and evolutionary patterns that involve massive randomness or overwhelming amounts of parallelism. Examples of various uses of this method are cited.