Cultivar

A cultivar is a domesticated plant selected by humans for specific desirable traits that it reliably passes on when propagated. Common propagation methods include division, cuttings from roots or stems, offsets, grafting, tissue culture, or carefully managed seed production. While most cultivars result from deliberate human breeding, some come from wild plants with naturally distinctive features. Cultivar names follow the rules of the International Code of Nomenclature for Cultivated Plants (ICNCP), and not every cultivated plant qualifies as a cultivar.

Horticulturists generally believe the term "cultivar" was coined to mean "cultivated variety." Popular ornamental plants such as roses, camellias, daffodils, rhododendrons, and azaleas are often cultivars, developed through breeding, selection, or sports to enhance flower color, size, plant shape, or other traits. Similarly, nearly all agricultural food crops are cultivars selected for improved yield, flavor, or disease resistance. Since genetic engineering emerged in the 1970s and was applied to crop breeding in the 1980s, very few wild plants are now used as commercial food sources. Trees in forestry are also specially selected cultivars grown for better timber quality and yield; for example, the American timber company Weyerhaeuser is the leading grower of genetically modified Douglas-fir trees, one of the most commonly harvested species.

Cultivars form a major part of Liberty Hyde Bailey's broader group, the cultigen, defined as a plant whose origin or selection is primarily due to intentional human activity. A cultivar is not the same as a botanical variety, which is a taxonomic rank below subspecies, and the rules for naming and using botanical varieties differ from those for cultivars. Since the Plant Patent Act of 1930, cultivar naming has been complicated by statutory plant patents and plant breeders' rights. The International Union for the Protection of New Varieties of Plants (UPOV) provides legal protection for plant cultivars to individuals or organizations that introduce new cultivars commercially.

UPOV requires that a cultivar be "distinct," "uniform," and "stable." To be distinct, it must have characteristics that easily set it apart from any other named cultivar. To be uniform and stable, it must retain these traits through repeated propagation. Naming cultivars is a key part of cultivated plant taxonomy, governed by the Rules and Recommendations of the International Code of Nomenclature for Cultivated Plants (ICNCP, often called the Cultivated Plant Code). A cultivar name consists of the scientific Latin botanical name followed by a cultivar epithet.

Etymology

The epithet is usually in a vernacular language, and this is required for cultivars named after January 1, 1959. The word "cultivar" arose from the need to distinguish wild plants from those with characteristics that emerged in cultivation, now called cultigens. This distinction dates back to the Greek philosopher Theophrastus (370–285 BC), the "Father of Botany," who was keenly aware of the difference. Botanical historian Alan Morton noted that Theophrastus, in his Historia Plantarum (Enquiry into Plants), "had an inkling of the limits of culturally induced (phenotypic) changes and of the importance of genetic constitution" (Historia Plantarum, Book 3, 2, 2 and Causa Plantarum, Book 1, 9, 3).

The International Code of Nomenclature for algae, fungi, and plants takes as its starting point for modern botanical nomenclature the Latin names in Linnaeus' (1707–1778) Species Plantarum (tenth edition) and Genera Plantarum (fifth edition). In Species Plantarum, Linnaeus listed all plants he knew, either directly or from his extensive reading. He recognized the rank of varietas (botanical "variety," below species and subspecies) and indicated these varieties with Greek alphabet letters such as α, β, and δ before the varietal name, rather than using the abbreviation "var." as is common today. Most of the varieties Linnaeus listed were of "garden" origin rather than wild plants.

Over time, the need to distinguish wild plants from cultivated variations grew. In the nineteenth century, many "garden-derived" plants received horticultural names, sometimes in Latin and sometimes in vernacular languages. From around the 1900s, cultivated plants in Europe were recognized in Scandinavian, Germanic, and Slavic literature as stamm or sorte, but these terms could not be used internationally because international agreements required new denominations to be in Latin. In the twentieth century, an improved international nomenclature for cultivated plants was proposed.

Liberty Hyde Bailey of Cornell University in New York, United States, coined the word "cultivar" in 1923 when he wrote: "The cultigen is a species, or its equivalent, that has appeared under domestication – the plant is cultigenous. I now propose another name, cultivar, for a botanical variety, or for a race subordinate to species, that has originated 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." In that essay, Bailey used only the rank of species for the cultigen, but it was clear to him that many domesticated plants were more like botanical varieties than species, and that realization likely motivated his suggestion of the new category of cultivar. Bailey created the word "cultivar."