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  • The action or process of placing a group of organisms on a specific level in a taxonomic hierarchy.
    taxonomy grouping rank

    In retrospect it has become evident that great confusion was caused by the application of the term “species” to two fundamentally different logical categories [...]. The species taxon must be sharply distinguished from the species category. The specis category is the class, the members of which are species taxa. The particular definition of the species category which an author adopts determines which taxa he must rank as species [...]. The determination of species status is thus a two-step procedure. The first step consists of the delimitation of the presumptive species taxon against others and the second is the ranking of the given taxon into the appropriate category, for example, “population,” “subspecies,” or “species.” [...] Most taxonomists, including myself, were confused about this until a few years ago.

    Mayr, E. (1982). The Growth of Biological Thought. Diversity, Evolution, and Inheritance:253-4. 


    Determining species status is logically a two-step procedure involving first grouping and then ranking. It follows, I think, that there must be two parts to a complete concept or definition of species (or of any other taxonomic category)—a group-forming criterion and a criterion for assigning rank. […] Rather than recognize as a species every distinguishable clone, it might be desirabie to employ some other ranking criterion so as to choose more inclusive monophyletic units. Such ranking criteria might include ecological or morphological gaps (perhaps measured in terms of the number of apormorphies). In some cases information about breeding might also enter into the decision.

    Donoghue, M.J. (1985). A critique of the biological species concept and recommendations for a biological alt yyernative. Bryologist 88, 172-181: 176; 179.