Cultigen

A cultigen is a plant that has been deliberately altered or selected by humans; it is man-made (human-altered) or anthropogenic. Anthropogenic plants are derived and used almost exclusively within horticulture, agriculture and forestry. The following plants are cultigens:

• plants with cultivar and Group (formerly Cultivar-group) names. This comprises by far the greatest number of cultigens and includes:
  • selections of variants from the wild or cultivation
  • plants that are the result of breeding and selection programs
  • genetically modified plants (plants modified by the deliberate implantation of genetic material)
  • the graft-chimaera (plants grafted to produce mixed tissue, the graft material possibly from wild plants, special selections, or hybrids)

For the full range of plants that are given cultivar or Group names see International Code of Nomenclature for Cultivated Plants (ICNCP) and External Links below.

• anthropogenic plants that have not been given cultivar or cultivar group names. This includes:
  • unnamed plants that are the result of breeding, selection, and tissue grafting
  • ancient cultigens - plants with binomials (i.e. without cultivar names) that occur in the wild but which have undergone selection and distribution by humans for so long that their original ancestral distributions and forms in the wild are uncertain or unknown
  • unnamed (presumed) anthropogenic plants no longer known in the wild

Many ancient cultigens are precursors of important economic crops like Maize, Zea mays and Banana, Musa x cavendishii.

All plants in the above groupings remain cultigens when they are growing in the wild, whether they are naturalised or deliberately planted.

Formal definition

A cultigen is a plant whose origin or selection is primarily due to intentional human activity.

Origin of term

The word cultigen was coined in 1918 by American 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 Code of Botanical Nomenclature (ICBN).

In 1923 Bailey extended his original discussion pointing out that, at the rank of species, it was possible to distinguish two groups of plants, the cultigen and the indigen. He referred to indigens as:

" those that are discovered in the wild "

and cultigens as plants that:

" arise in some way under the hand of man "

He then defined a cultigen as:

... " a species, or its equivalent, that has appeared under domestication " ...

Cultigens and cultivars

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”. 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” and “variety” which seems more appropriate . 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 (see current definition in cultivar).

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 taxonomic (classification) category.

Usage

Bailey's last definition

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:

" Plant or group known only in cultivation; presumably originating under domestication; contrast with indigen "

This, in essence, is the definition given at the head of this piece. This last definition of the cultigen permits the inclusion of cultivars, unlike the 1923 definition which restricts the idea of the cultigen to plants at the rank of species.

Usage in botany

In botanical literature the word cultigen is used for plants that have been given binomials and are now known only in cultivation (as plants of unknown origin, generally presumed to be human selections) but there is no essential difference in principle between these ancient plants and modern plants altered by human activity that are named under the International Code of Nomenclature for Cultivated Plants (ICNCP). The use of a Latin binomial (only) for such plants seems misleading (even though it is permissible under the ICBN) because binomials are overwhelmingly used for “wild” plants, and cultivar names used for virtually all cultigens.

The use of cultigen in this botanical sense essentially follows Bailey's definition of cultigen given in 1923.

Usage in horticulture

In horticulture the definition and use of the term cultigen has varied but generally, unlike usage in botany, it encompasses cultivars. One example is the definition given in the Botanical Glossary of The New Royal Horticultural Society Dictionary of Gardening which defines cultigen as:

" A plant found only in cultivation or in the wild having escaped from cultivation; included here are many hybrids and cultivars, "...

The use of cultigen in this sense is essentially the same as the last definition of the cultigen published by Bailey in 1924.

Other usage

The term cultigen is occasionally applied in a very general sense to any organisms that do not have a wild or uncultivated counterpart, see for example . Animal breeds raised in captivity would be included here. It might seem that the word "domesticate" could serve the same purpose as cultigen. However, the widely held view that domesticated plants and animals are simply wild plants and animals used in domestic situations (often as tamed wild animals, or plants introduced directly from the wild, rather than being specially selected for particular desirable characteristics) would not support this view. However there is debate about what constitutes domestication and some authors maintain that to be termed domesticated or a "domesticate" a plant or animal must have been "changed" in some way from its wild counterparts. Regardless of this debate, it is clear that the term cultigen originated within horticulture and botany and that these areas are where it has mostly been applied.

Recommended usage

Wider use of the term cultigen as defined here has been proposed for the following reasons:

• supports the intent of Bailey's last definition of 1924
• 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 ICNCP, 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 ICNCP
• gives greater precision and clarity to the definition of the respective scope, terminology and concepts of the International Code of Botanical Nomenclature (ICBN) and the International Code of Nomenclature for Cultivated Plants (ICNCP)
• avoids the potential for confusion within the ICNCP 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)
    • simply providing a mechanism for allocating names to those “cultivated” plants requiring special categories outside the Linnaean hierarchy of the ICBN .

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.

• • What exactly does altered mean?

There are cases that do not seem to comply with the definition. For example, we can presume that the entire global flora is changing as a result of human-induced climate change. Does this mean that all plants are cultigens?

In cases like this the definition refers to "deliberate" selection and this would be of particular plant characteristics that are not exhibited by a plant's wild counterparts (but see Selections from the wild).

• • What exactly does selected mean?

From the moment a plant is taken from the wild it is subject to human selection pressure - from the selection of the original propagation material to the purchase of the plant in a nursery. Does this mean that all cultivated plants are cutigens?

In cases like this the definition implies plants that have been deliberately selected, generally for commercial or aesthetic reasons; they have characteristic(s) that distinguish them from their wild counterparts and are almost always named.

• • What about plants selected from the wild?

Plants like Quercus robur, Oak, Liquidambar styraciflua, Liquidamber and Eucalyptus globulus, Blue Gum grown in parks and gardens are essentially the same as their wild counterparts and are therefore not cultigens. However, occasionally within natural plant variation there occur characters that are of value to horticulture but of little interest to botany. For example a plant might have flowers of several different colours but these may not have been given formal botanical names. It is customary in horticulture to introduce such variants to commerce and to give them cultivar names. Technically these plants have not been deliberately altered in any way from plants growing (or once growing) in the wild but as they are deliberately selected and named it seems permissable to refer to them as cultigens. These occurrences are very few. The definition could be (clumsily) extended by mentioning that selection can be for "desirable variation that is not recognised in botanical nomenclature" (which excludes those plants simply transferred from the wild into cultivation).

• • What about gene flow between populations?

Occasionally cultigens escape from cultivation into the wild where they breed with indigenous plants. Selections may be made from the progeny in the wild and brought back into cultivation where they are used for breeding and the results of the breeding again escape into the wild to breed with indigenous plants. Lantana has behaved much like this. The genetic material of a cultigen may become part of the gene pool of a population where, over time, it may be largely or completely swamped. In cases like this what plants are to be called cultigens?

Whether a plant is a cultigen or not does not depend on where it is growing. If it complies with the definition then it is a cultigen. Cases like this have always been difficult for botanical nomenclature. Unnamed progeny in the wild might be given a name like Lantana aff. camara (aff. = having affinities with) or may remain unnamed. Its cultigenic origin may or may not be recognised by the allocation of a cultivar name.

• • Plants of unknown origin

Occasionally plants will occur whose origin is unknown. Plants growing in cultivation that are unknown in the wild may be determined as cultigenic as a result of scientific investigation, but may remain a mystery.

• • Difficult cases

It may happen that a hybrid cross that has occured in nature is also perfomed deliberately in cultivation and that the progeny appear identical. How do we know which plants are cultigens?

If the cross in cultivation is followed by deliberate selection and naming then this will indicate a cultigen. However in a case like this it may not be possible to tell.

Etymology: culti(vated) or culti(cultigen) + gen (gens Latin - kind)

See also Domestication of plants.

Further reading

Spencer, R.D. and Cross, R.G. 2007. The cultigen. Taxon 56(3):938-940

Spencer, R, Cross, R & Lumley, P. 2007. (3rd edn) Plant names: a guide to botanical nomenclature. CSIRO Publishing, Collingwood, Australia. (Also CABI International Wallingford, UK. The definition of cultigen given in the Glossary of this reference does not include deliberately selected plants that are identical to plants growing (or once growing) in the wild.

External Links

• [3] A definition of cultigen extending beyond the sphere of plants
• [4] International Society for Horticultural Science (includes useful links)