Charles Darwin ‘The Variation of Animals and Plants under Domestication’ (1868)
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.
Almost all agricultural plants are cultigens, many trees used in forestry are cultigens, and most of the plants used in horticulture are cultigens (like the multitude of rose and camellia cultivars). However, many garden plants are also genetically indistinct from wild plants. In general cultigens can be distinguished from plants that are genetically identical to those growing in the wild by their names – for example the cultivars Rosa ‘Peace’, Camellia x williamsii ‘Anticipation’ (which are cultigens) are distinguished from the non-manipulated wild plants Cornus capitata, Quercus robur, Cedrus deodara, and Eucalyptus crenulata.
Domesticated plants (cultigens)
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.
Cultigens have originated in various ways:
• Simple selections of variants taken from plants in the wild or in cultivation, notably ancient selections of crops of uncertain origin and unknown in the wild
• Artificial hybrids produced both by accident and intention
• Clonal material reproduced by cuttings, grafting, budding, layering etc.
• Graft-chimaeras (plants grafted with tissues from different species)
• Selections of aberrant growth such as witches’ brooms
• As 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
The first cultigens were probably the agricultural cereal crops that arose about 12,000 years ago.
It was not until Roman times that cultigens would be given the names needed to distinguish one from another. Botanical historian 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.
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).
Plant nomenclature was given a boost when the Lois de la Nomenclature Botanique (Laws of Botanical Nomenclature) were formulated at an International Botanical Congress convened in Paris in 1867. This system of nomenclatural rules, now regularly updated, is known as the Botanical Code or, more formally, the International Code of Nomenclature for algae, fungi, and plants (ICN), or, this title established at the Melbourne Botanical Congress of 2011. Then in 1953 a separate Code was dedicated to the names of cultigens, the 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)(Brickell, C.D. et al. 2009).
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.
The word ‘cultigen’ (Latin cultus – cultivated, and gens – kind) originated in 1918, coined by Liberty Hyde Bailey (1858–1954) an American horticulturist and botanist who noted that plants altered by humans needed special classification categories because they did not fit neatly into the hierarchical system devised by Linnaeus (Bailey 1918). Bailey was echoing again the 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.’
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 ICNCP 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.
Commentary & sustainability analysis
Cultigens are important because over time, and as human population and economic activity has increased, natural landscapes of the world consisting of wild plants have been progressively converted into cultural landscapes consisting mostly of cultigens. Part of this process has been a consequence of the appropriation of vast areas of arable land for the cultivation of food crops, but also to a lesser extent the desire for ornamental plants and the and the introduction of them as part of a global plant exchange that gathered momentum in the 17th century. This was facilitated by: botanic gardens, improved transport and communication systems, the commercializtion of plants through plant nurseries, the advent of genetics and plant breeding and, most recently, the use of genetic engineering.