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 with commercial value used in horticulture, agriculture or 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 Nomenclature for algae, fungi, and plants, 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 International Code of Nomenclature for Cultivated Plants (ICNCP) 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 ICNCP does not recognize the use of trade designations and other marketing devices as scientifically acceptable names, but does provide advice on how they should be presented.
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 ICNCP.
A cultigen is a plant whose origin or selection is primarily due to intentional human activity.
The wild/cultivated distinction
Interest in the distinction between wild and cultivated plants dates back to antiquity. Botanical historian Alan Morton notes that wild and cultivated plants (cultigens) were of intense interest to the ancient Greek botanists (partly for religious reasons) and that the distinction was discussed in some detail by Theophrastus (370–285 BCE) the "Father of Botany". Theophrastus was a pupil of both Plato and Aristotle and succeeded the latter as head of the Peripatetic School of Philosophy at the Lyceum in Athens. Theophrastus accepted the view that it was human action, not divine intervention, that produced cultivated plants (cultigens) from wild plants and he also "had an inkling of the limits of culturally induced (phenotypic) changes and of the importance of genetic constitution" (Historia Plantarum III, 2,2 and Causa Plantarum I, 9,3). He also noted that cultivated varieties of fruit trees would degenerate if cultivated from seed.
Origin of term
The word cultigen was coined in 1918 by Liberty Hyde Bailey (1858–1954) an American horticulturist, botanist and cofounder of the American Society for Horticultural Science. He was aware of the need for special categories for those cultivated plants that had arisen by intentional human activity and which would not fit neatly into the Linnaean hierarchical classification of ranks used by the International Rules of Botanical Nomenclature (which later became the International Code of Nomenclature for algae, fungi, and plants).
In his 1918 paper Bailey noted that for anyone preparing a descriptive account of the cultivated plants of a country (he was at that time preparing such an account for North America) it would be clear that there are two gentes or kinds (Latin singular, gens; plural, gentes) of plants. Firstly, those that are of known origin or nativity "of known habitat". These he referred to as indigens. The other kind was:
He called this second kind of plant a cultigen, the word derived from the conflation of the Latin cultus – cultivated, and gens – kind.
In 1923 Bailey extended his original discussion emphasising that he was dealing with plants at the rank of species and he referred to indigens as:
and cultigens as plants that:
He then defined a cultigen as:
Bailey soon altered his 1923 definition of cultigen when, in 1924, he gave a new definition in the Glossary of his Manual of Cultivated Plants as:
This, in essence, is the definition given at the head of this piece. This definition of the cultigen permits the recognition of cultivars, unlike the 1923 definition which restricts the idea of the cultigen to plants at the rank of species.
In later publications of the Liberty Hyde Bailey Hortorium, Cornell, the idea of the cultigen having the rank of species returned (e.g. Hortus Second in 1941 and Hortus Third in 1976): both of these publications indicate that the terms cultigen and cultivar are not synonymous and that cultigens exist at the rank of species only.
Recent usage in horticulture has, however, maintained a distinction between cultigen and cultivar while nevertheless allowing the inclusion of cultivars within the definition (see "Usage in horticulture" below).
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), while cultivar is a formal classification category (in the 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. Bailey was never explicit about the etymology of the word cultivar and it has been suggested that it is a contraction of the words "cultigen" or "cultivated" and "variety". He defined cultivar in his 1923 paper as:
This definition and understanding of cultivar has changed over time (see current definition in cultivar).
In botanical literature the word cultigen is generally used to denote a plant which, like the bread wheat (Triticum aestivum) is of unknown origin, but presumed to be an ancient human selection. Plants like bread wheat have been given binomials according to the Botanical Code and therefore have names with the same form as those of plant species that occur naturally in the wild, but it is not necessary for a cultigen to have a species name, or to have the biological characteristics that distinguish a species. Cultigens can have names at any of various other ranks, including cultivar names, names in the classification categories of grex and group, variety names, forma names, or they may be plants that have been altered by humans (including genetically modified plants) but which have not been given formal names.
The year 1953 was an important one for cultivated plant taxonomy because this was the date of publication of the first International Code of Nomenclature for Cultivated Plants in which Bailey's term cultivar was introduced. It was also the year that the eponymous journal commemorating the work of Bailey (who died in 1954), Baileya, was published. In the first volume of Baileya taxonomist and colleague of Bailey, George Lawrence, wrote a short article clarifying the distinction between the new term cultivar and the variety. In the same article he also tried to clarify the critical term taxon which had been introduced by German biologist Meyer in the 1920s but had only just been introduced and accepted in botanical circles. This brief article by Lawrence is useful for its insight into the understanding of the meaning of the word cultigen at this time. He opens the article:
In horticulture the definition and use of the terms cultigen and cultivar has varied. One example is the definition given in the Botanical Glossary of The New Royal Horticultural Society Dictionary of Gardening which defines cultigen as:
The use of cultigen in this sense is essentially the same as the definition of the cultigen published by Bailey in 1924.
The Cultivated Plant Code, however, states that cultigens are "maintained as recognisable entities solely by continued propagation", and thus would not include plants that have evolved subsequent to escape from cultivation.
Wider use of the term cultigen as defined here has been proposed for the following reasons:
- supports current usage in horticulture
- assists clarity in non-technical discussions about "wild" and "cultivated" plants (for example, cultivated plants as commonly understood (plants in cultivation) are not the same as the "cultivated plants" of the Cultivated Plant Code, and the distinction between "wild" and "cultivated" habitats is becoming progressively blurred)
- has the potential to simplify the language and definitions used in the Articles and Recommendations of the Cultivated Plant Code
- gives greater precision and clarity to the definition of the respective scope, terminology and concepts of the Botanical Code and the Cultivated Plant Code
- avoids the potential for confusion within the Cultivated Plant Code over its scope, that is, whether it is concerned with: where plants are growing (in the wild or in cultivation) how they originated (whether they are the result of intentional human activity or not) whether it simply provides a mechanism for regulating the names of those cultigens requiring special classification categories that are not part of the Linnaean hierarchy of the Botanical Code i.e. cultivar and Group names
Critique of definition
Potential misunderstandings and questions arising from the definition of cultigen given here have been discussed in the literature and are summarised below.
- Natural and artificial selection
- What exactly does altered mean?
- What exactly does deliberately selected mean?
- What about plants selected from the wild?
- What about gene flow between populations?
- Plants of unknown origin
- Difficult cases