A cultigen (from the Latin cultus - cultivated, and gens - kind) is a plant that has been deliberately altered or selected by humans; it is the result of artificial selection. These "man-made" or anthropogenic plants are, for the most part, plants of commerce that are used in horticulture, agriculture and forestry. Because cultigens are defined by their mode of origin and not by where they are growing, plants meeting this definition remain cultigens whether they are naturalised in the wild, deliberately planted in the wild, or growing in cultivation. Cultigens arise in the following ways: selections of variants from the wild or cultivation including vegetative sports (aberrant growth that can be reproduced reliably in cultivation); plants that are the result of plant breeding and selection programs; genetically modified plants (plants modified by the deliberate implantation of genetic material); and graft-chimaeras (plants grafted to produce mixed tissue, the graft material possibly from wild plants, special selections, or hybrids).
Cultigens may be named in any of a number of ways. The traditional method of scientific naming is under the International Code of Botanical Nomenclature, and many of the most important cultigens, like maize (Zea mays) and banana (Musa acuminata), are so named. Although it is perfectly in order to give a cultigen a botanical name, in any rank desired, now or at any other time, these days it is more common for cultigens to be given names in accordance with the principles, rules and recommendations laid down in the Cultivated Plant Code which provides for the names of cultigens in three classification categories, the cultivar, the Group (formerly Cultivar-group), and the grex. From that viewpoint it may be said that there is a separate discipline of cultivated plant taxonomy, which forms one of the ways to look at cultigens. The Cultivated Plant Code does not recognize the use of trade designations and other marketing devices as scientifically acceptable names.
Not all cultigens have been given names according to the Cultivated Plant Code. Apart from ancient cultigens like those mentioned above there may be occasional anthropogenic plants such as those that are the result of breeding, selection, and tissue grafting that are of no commercial value and have therefore not been given names according to the Cultivated Plant Code.
Read more about Cultigen: Formal Definition, The Distinction "wild" and "cultivated", Origin of Term, Bailey's Definitions, Cultigens and Cultivars, Recommended Usage, Critique of Definition