XXV.2.3 Evolutionary systematists try to classify organisms using a closed system of taxa of various taxonomic levels, while cladists must usually do without such a closed system
Evolutionary systematists took a formalized Linnaean system of taxa at various levels, including their nomenclature, from their structuralistically oriented predecessors. They differentiated the originally hierarchical system of organisms into the lowest super-species level of the genus and then gradually into the family, order, class and phylum. As this number of hierarchical levels (ranks) was insufficient for some evolutionary lines, further levels were gradually introduced; for example supplementary categories were created by adding the prefixes sub-, super- and infra- and thus, for example, subgenuses, subfamilies, infrafamilies, superfamilies, and additional categories, for example tribes and cohorts. Basically, it is a matter of convention which taxonomic levels are differentiated for the individual taxon. For example, it is certainly not possible to compare taxa at the same level that belong to different groups of organisms, such as the families of crustaceans and families of birds, on the basis of their evolutionary age or degree of mutual phenotype similarity of their members. In the past, attempts were made to determine the level of a taxon on the basis of its evolutionary age, but this approach has not become established.
Cladists were forced by objective circumstances to abandon the system of formal taxonomic ranks. As they attempted to create a system of strictly monophyletic taxa (see below), the number of taxonomic levels increased disproportionately, so that it was no longer possible to introduce separate names for them. Consequently, cladists mostly restrict themselves to expressing the rank of a taxon by a number or graphically, by placing (offsetting) the relevant name of the taxon (in cladistic terminology, clad) on the page. They do not attempt to classify the created clads into predetermined categories according to their taxonomic rank. Consequently, evolutionary taxonomists sometimes (pejoratively) call their work, not classification but rather cladification. The cladistic system is less illustrative and less didactic, but contains all the information obtained on the cladogenesis of the studied evolutionary line.