hierarchical classification

A system in which individuals are grouped into an ascending series of successively larger and broader categories, so that lower groups are always subordinate to, and included in, those that are higher in the hierarchy. Within the hierarchy, classification is based on the affinities of the component units. The order in which the 12 principal ranks are used is governed by the *International Code of Botanical Nomenclature and, although all available ranks in the hierarchy need not be used, their sequential order must not be altered. In ascending order the ranks are: form, variety, species, series, section, genus, tribe, family, order, class, division, and kingdom. Additional subcategories can also be designated (e.g. subseries and subclass) thus further extending the total number of ranks to 24.