Cultigen

A cultigen is a plant that is the result of artificial selection by humans. Liberty Hyde Bailey, an American botanist was the first to use the term, in 1918.Bailey L.H. 1918. The indigen and cultigen. Science series 2, 47:306-308 Bailey noticed that the classification Linné introduced for plants was not useful for classifying plants which came from human cultivation and selection. He called the plants which grow in the wild without human selection indigens. A cultigen was: " ... a domesticated group of which the origin may be unknown...  [It has] such characters as to separate it from known indigens, and is probably not represented by any type specimen or exact description".  The point is that a cultigen cannot always be placed in the traditional Linnean system of botanical classification.

Bailey later changed his definition to "Plant or group known only in cultivation; presumably originating under domestication; contrast with indigen", which is the definition used above. Examples of cultigens are maize and cabbage.

 Cultigens and cultivars 
Cultigen and cultivar may be confused with one-another. Cultigen is a general-purpose term encompassing not only plants with cultivar names but others as well (see introductory text above). Cultivar is a formal classification category in the International Code of Nomenclature for Cultivated Plants (ICNCP).

Although in his 1923 paper Bailey used only the rank of species for the cultigen, it was clear to him that many domesticated plants were more like botanical varieties than species and so he established a new classification category for these, the cultivar, generally assumed to be a contraction of the words “cultivated” and “variety”.Trehane P. 2004. 50 years of the International Code of Nomenclature for Cultivated Plants. Acta Horticulturae 634: 17-27. He defined cultivar in his 1923 paper as:  ... "a race subordinate to species, that has originated and persisted under cultivation; it is not necessarily, however, referable to a recognised botanical species. It is essentially the equivalent of the botanical variety except in respect to its origin".

This definition and understanding of cultivar has changed over time.

 Definition of cultigen 
The definition has been discussed:
The selection process is called artificial if humans cause it. This does not mean humans are not part of nature, it is simply a way to distinguish natural selection from human-influenced (artificial selection)
What is the meaning of altered? The whole flora is changing because of climate change, which humans inflenced, yet no one would say that all the plants changing because of climate change are cultigens.
Some plants are used in gardens or parks. They are the same that those that occur in nature.
There may be gene flow from a cultigen that escaped into the wild and an indigen. There may be a practical problem of how to name such plants. 
Some plants have an unknown origin; it is therefore impossible to say if they are cultigens.
Some crossings that are used in cultivation, may also occur in the wild. This makes the classification problematic.

References

Category:Botany