Man-made plants

For a brief historical summary of the way that cultivated plants have become an ever-increasing component of the worlds vegetation and landscapes see cultivated plant globalization.

Introduction – Man-Made Plants

Human impact on the Earth’s global flora is most clearly demonstrated by changes in historical patterns of plant distribution – notably changes in human-induced species composition and biomass.  This is most starkly represented by the relative proportions and distribution of wild and cultivated plants across the planetary surface. The most dramatic changes to plants themselves are a consequence of human selection, breeding, and genetic engineering.

Man-made or anthropogenic plants (technically referred to as cultigens) are those plants that have been genetically altered or specially selected for human use. Most cultigens differ genetically from their wild relatives.

The coevolution of plants and people has been a reciprocal process. Plant domestication is thought to have gathered momentum with the domestication of plants during the Neolithic Agricultural Revolution when human plant selection began the process of human influence on plant genetics. However, there is a compelling sense in which plants were the agents – that it was because of the enforced sedentary urbanization that followed necessarily from the development of agriculture that human foragers and nomadic hunter-gatherers became ‘civilized’.

Over the last 100 years or so, under the impact of an increased food supply generated by industrial agriculture, an exploding human population has converted natural landscapes consisting of wild plants into cultural landscapes comprised of cultivated plants, almost all of these man-made (cultigens). The cultivated plants of both garden and field have escaped into the wild at the expense of indigenous flora.

Cultigens are plants of commerce produced for use in forestry, agriculture and horticulture. Those produced for forestry are relatively few: the remainder can be conveniently divided into staple agricultural cereals, horticultural crops, and ornamental plants. Included under these categories would be smaller operations like market gardens, vineyards, orchards, and plant cultivation for floristry.

Cultigens are important because, over time and as human population has increased, partly as a consequence of the global distribution of agricultural and horticultural crops, natural landscapes of the world consisting of wild plants have been progressively converted into cultural landscapes consisting mostly of cultigens.

Vast areas of arable land have been appropriated for the cultivation of food crops, but also to a lesser degree the desire for ornamental plants and the introduction of ornamental plants as part of a global plant exchange that gathered momentum with the global plant exchange in the 17th century and reached a peak in the 18th century. This was facilitated by: botanic gardens, improved transport and communication systems, the commercialization of plants through plant nurseries. In recent times additional momentum has been provided by the advent of genetics and plant breeding and, most recently, the use of genetic engineering.

Cultigens are plants of commerce produced for use in forestry, agriculture and horticulture. Those produced for forestry are relatively few: the remainder can be conveniently divided into staple agricultural cereals, horticultural crops, and ornamental plants. Cultigens are important because, over time and as human population has increased, partly as a consequence of the global distribution of agricultural and horticultural crops, natural landscapes of the world consisting of wild plants have been progressively converted into cultural landscapes consisting mostly of cultigens. Part of this has been a consequence of the appropriation of vast areas of arable land for the cultivation of food crops, but also to a lesser degree the desire for ornamental plants and the introduction of ornamental plants as part of a global plant exchange that began in the seventeenth century, facilitated by botanic gardens, and gathering momentum with improved transport and communication systems, the commercialization of plants through plant nurseries, the advent of genetics and plant breeding and, most recently, the use of genetic engineering.

Plant domestication and plant cultivation

Plant domestication and plant cultivation are overlapping ideas but it is important to distinguish between the two. For our purposes plant domestication refers to the modification of plants for human purposes: that is, the genetic alteration of plants so that they have characteristics that are not found in wild plants. Since the application of the expression ‘domesticated plants’ is ambiguous, plants that have been genetically altered in this way have been called anthropogenic plants or, for simplicity and precision, cultigens.^[1][2][3]

Almost all agricultural plants are cultigens, as are many of the trees used in forestry, and most of the popular plants used in horticulture (like the multitude of rose and camellia cultivars). However, many garden plants are also genetically indistinct from wild plants, being plants introduced directly from the wild into cultivation.

Cultigens

For simplicity, man-made (anthropogenic) plants are now referred to collectively as cultigens.^[3]{4]

Included under this category would be the following:

. Ancient selections of crops often of uncertain origin and unknown in the wild
. Simple selections of variants taken from plants in the wild or in cultivation
. Artificial hybrids produced both by accident and intention
. Clonal material reproduced by cuttings, grafting, budding, layering, etc
. Graft-chimaeras
. Selections of aberrant growth such as witches brooms
. The progeny of deliberate repeatable single crosses between two pure lines that produce plants of a
particular phenotype that is desirable for horticulture, but which are not genetically identical
. Plants produced by genetic engineering

Definition

Cultigens are formally defined in the Cultivated Plant Code as plants ‘… whose origin or selection is primarily due to the intentional actions of mankind’, and they ‘require use of the special classification categories cultivar, Group and grex’, which are rank-like names resembling, but not equivalent to, ranks like family, genus and species in the ICN.

Cultivar

For horticulturists it is important to distinguish between cultigens and cultivars.

In a following paper Bailey defined indigens as ‘those that are discovered in the wild’ noting that cultigens ‘arise in some way under the hand of man’ and in this paper he coined the term ‘cultivar’, a contraction of ‘cultivated variety’, to be used as a taxonomic category (‘cultigen’ is a general-purpose term) for plant variants arising in cultivation (Bailey 1923).

The Cultivated Plant Code of 2009 defines the cultivar as ‘ . . . an assemblage of plants that (a) has been selected for a particular character or combination of characters, (b) is distinct, uniform and stable in those characters, and (c) when propagated by appropriate means, retains those characters.’ (Brickell et al. 2009). The word ‘cultivar’ is now the most widely used taxonomic term in cultigen taxonomy, introduced to the wider horticultural community with the first Cultivated Plant Code in 1953.

Etymology

The word ‘cultigen‘ (Latin cultus – cultivated, and gens – kind) was coined in 1918 by Liberty Hyde Bailey (1858-1954), an American horticulturist and botanist who realized that plants altered by humans needed special classification categories because they did not fit neatly into the hierarchical system devised by Linnaeus^[1]. Bailey was again echoing Theophrastus‘s distinction between ‘wild’ and ‘man-made’ or ‘cultivated” plants. He called ‘wild’ plants indigens and ‘man-made’ plants cultigens, the latter being: – a domesticated group of which the origin may be unknown or indefinite, which has such characters as to separate it from known indigens, and which is probably not represented by any type specimen or exact description, having therefore no clear taxonomic beginning. ^{[1,p. 306]}

Origin

The first cultigens were probably the agricultural cereals that arose about 12,000 years ago ^[5] but we have no record of any special names given to cultigens until Roman times. Morton notes that Theophrastus refers to wheat varieties (HP VIII, 1, 2-7) and Roman agricultural writer Columella (4-c. 70 CE) mentions selections of carrots in his De Re Rustica ix,4,5. Botanical historian William Stearn attributes the first record of named cultigens to the Roman statesman Cato the Elder (234-149 BCE) who, writing in De Agri Cultura in about 160 BCE, named 120 kinds (what we would now call cultivars or cultivated varieties) of figs, grapes, apples and olives.^[6]

Pliny the Elder (HN 15.15) refers to the tradition of obtaining celebrity by naming new and improved grafted varieties of fruit as a commemoration of estates or their owners.

Garden cultigens

While devising his system of plant classification and nomenclature Linnaeus was constantly frustrated by the multicoloured and other ornamental cultigens so adored by the non-scientific gardening community. He disparagingly labelled these people anthophiles’ (flower lovers):

botany has been overborne by the system of varieties for long enough … few, if any, agree as to what constitutes a species, or what a variety; … I wish the system of varieties were entirely excluded from Botany and turned over entirely to the Anthophiles, since it causes nothing but ambiguities, errors, dead weight and vanity (Linnaeus 1737)

He added much later

‘… no botanist in his senses will enlist in their camp‘ (Linnaeus 1751, aphorism 310, transl. Stafleu 1971).

Like many scientists of his day Linnaeus believed in natural theology – that the order of the plant kingdom was evidence for the order placed in nature by God and species were immutable. Cultigens were not a part of the natural order.

All the species recognized by Botanists came forth from the Almighty Creator’s hand, and the number now and always will be exactly the same, while every day new and different florist’s species arise from the true species recognized by botanists, and when they have arisen they eventually revert to their original forms. (Linnaeus 1751, aphorism 310, transl. Stafleu 1971).

The genetic complexity of human-altered plants, their absence from the evolutionary process of natural descent with modification, has resulted in difficulties with their classification and therefore continued neglect by botanists today.

Naming

It was not until Roman times that cultigens would be given the names needed to distinguish one from another. Botanical historian Morton notes that Theophrastus refers to wheat varieties (Historia Plantarum VIII, 1, 2-7) and Roman agricultural writer Columella (4- c. 70 CE) mentions selections of carrots (De Re Rustica ix,4,6).

Botanical historian William Stearn attributes the first named cultigens to the Roman statesman Cato the Elder (234–149 BCE) who, writing in his De Agri Cultura in about 160 BCE, named 120 different kinds of what we would now call cultivars (cultivated varieties) of figs, grapes, apples and olives.^[5]

In the modern era Linnaeus, while working on his theory of plant classification and nomenclature, was constantly frustrated by the different colours and forms of garden cultigens so beloved by the gardening community. He disparagingly called these people ‘anthophiles’ (flower lovers): ‘ .. botany has been overborne by the system of varieties for long enough … few, if any, agree as to what constitutes a species, or what a variety; … I wish the system of varieties were entirely excluded from Botany and turned over entirely to the Anthophiles, since it causes nothing but ambiguities, errors, dead weight and vanity …’ (Linnaeus 1737) adding much later ‘… no botanist in his senses will enlist in their camp’ (Linnaeus 1751, aphorism 310, transl. Stafleu 1971). For Linnaeus cultigens were not a part of God’s natural order. ‘All the species recognized by Botanists came forth from the Almighty Creator’s hand, and the number now and always will be exactly the same, while every day new and different florist’s species arise from the true species recognized by botanists, and when they have arisen they eventually revert to their original forms.’ (Linnaeus 1751, aphorism 310, transl. Stafleu 1971).

Following the initial systematization of plant nomenclature by Linnaeus, further order was put into the developing chaos of plant names when the Lois de la Nomenclature Botanique (Laws of Botanical Nomenclature) were established at an International Botanical Congress convened in Paris in 1867. This system of nomenclatural rules has been regularly updated and is now known as the International Code of Nomenclature for algae, fungi, and plants (ICN), the current title coined at a Botanical Congress in Melbourne in 2011.

Although the difficulties with cultigens noted by the acerbic Linnaeus persisted, it would take until 1953, a date we can assign to the beginning of cultivated plant taxonomy, before his wish for a separate code would be granted with the publication of the first, Wageningen, International Code of Nomenclature for Cultivated Plants (ICNCP), abbreviated to Cultivated Plant Code. This was followed by seven subsequent editions – in 1958 (Utrecht), 1961 (update of 1958), 1969 (Edinburgh), 1980 (Seattle), 1995 (Edinburgh), 2004 (Toronto), and the latest in 2009 (Wageningen).^[2]

Cultigens are defined in the Cultivated Plant Code as plants ‘… whose origin or selection is primarily due to the intentional actions of mankind’ and they use of the special classification categories cultivar, Group and grex, which are names similar to ranking names like family, genus, and species in the ICNCP. The ICNCP names, sometimes called variety names, like Apple ‘Jonathan’ or Malus ‘Jonathan’, are in non-Latin form which helps the gardeners, nurserymen, farmers, foresters who use them. Wild plant taxonomy and cultigen taxonomy are both about the science of plant names but the former is plant-centred and the latter is human-centred, recalling the theme of studying plants either for their own sake or for their utility, as pure and applied science.

In general cultigen names are distinguished by having cultigen epithets – names, often in English, that supplement the usual Latin names and are presented within quotation marks. For example the cultivars Rosa ‘Peace’, Camellia x williamsii ‘Anticipation’ (which are cultigens) can be distinguished from the non-manipulated plants Cornus capitata, Quercus robur, Cedrus deodara, and Eucalyptus crenulata, the latter three species found both in the wild and in cultivation.

The plants of commerce

Botanical neglect of cultigens arises not only because they lie outside the evolutionary world of descent with modification but also because these are the plants of commercial enterprise.

In practical terms cultigen taxonomy serves a particular community of people – those requiring non-Latin names for plants available in the commercial worlds of agriculture, forestry and horticulture,
so it is farmers, foresters, horticulturists, nurserymen and gardeners who are the most frequent users of these names.

Wild plant taxonomy and cultigen taxonomy are both about the science of plant names, but the former is plant-centred and the latter is human-centred, recalling the theme of studying plants either for their own sake or for their utility, as pure and applied science.

First published on the internet – 1 March 2019
. . . 18 July 2022 – major revision
. . . 29 June 2023 – minor revision

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