In naming cultivated plants, a Group (with a capital G), previously called a cultivar-group, is a formal classification category in the International Code of Nomenclature for Cultivated Plants (ICNCP):

ICNCP Art. 3.1: "a formal category for assembling cultivars, individual plants or assemblages of plants on the basis of defined similarity."

Every word in a Group epithet (name) is capitalised, except where not permitted by English-language custom, e.g. conjunctions, prepositions (that do not begin the epithet), and words following a hyphen (that are not proper names). (Art. 21.3)