Used in many commercially important plant species and hybrids to distinguish major groups of cultivars sharing common characteristics. An example is the brassica vegetables, most of which are cultivars of the variable species Brassica oleracea. The cabbages, the cauliflowers, Brussels sprouts, broccolis and kales each constitute a cultivar group of this species. Cabbages, for example, were once designated Brassica oleracea var. capitata but modern principles of nomenclature demand that they now be named Brassica oleracea Capitata Group—this name covers numerous cultivars, some of which form subgroups, such as the Savoy cabbages. The thousands of cultivars in such complex hybrid groups as the roses, tulips and dahlias are generally classified into cultivar groups, sometimes in quite artificial ways.