A cultivar is a plant or grouping of plants selected for desirable characteristics that can be maintained by propagation. Most cultivars have arisen in cultivation but a few are special selections from the wild. Popular ornamental garden plants like roses, camellias, daffodils, rhododendrons, and azaleas are cultivars produced by careful breeding and selection for flower colour and form. Similarly, the world's agricultural food crops are almost exclusively cultivars that have been selected for characteristics such as improved yield, flavour, and resistance to disease: very few wild plants are now used as food sources. Trees used in forestry are also special selections grown for their enhanced quality and yield of timber.
Cultivars form a major part of Liberty Hyde Bailey's broader grouping, the cultigen, defined as a plant whose origin or selection is primarily due to intentional human activity. Cultivar was coined by Liberty Hyde Bailey and it is generally regarded as a portmanteau of "cultivated" and "variety", but could also be derived from "cultigen" and "variety". A cultivar is not the same as a botanical variety, and there are differences in the rules for the formation and use of the names of botanical varieties and cultivars. In recent times the naming of cultivars has been complicated by the use of statutory Plant Patents and Plant Breeders' Rights names.
The International Union for the Protection of New Varieties of Plants (UPOV – French: Union internationale pour la protection des obtentions végétales) offers legal protection of plant cultivars to people or organisations who introduce new cultivars to commerce. UPOV requires that a cultivar be distinct, uniform and stable. To be distinct, it must have characteristics that easily distinguish it from any other known cultivar. To be uniform and stable, the cultivar must retain these characteristics under repeated propagation.
The naming of cultivars is an important aspect of cultivated plant taxonomy, and the correct naming of a cultivar is prescribed by the Rules and Recommendations of the International Code of Nomenclature for Cultivated Plants (the ICNCP, commonly known as the Cultivated Plant Code). A cultivar is given a cultivar name, which consists of the scientific Latin botanical name followed by a cultivar epithet. The cultivar epithet is usually in a vernacular language. For example, the full cultivar name of the King Edward potato is Solanum tuberosum 'King Edward'. The 'King Edward' part of the name is the cultivar epithet which, according to the Rules of the Cultivated Plant Code, is bounded by single quotation marks.
The origin of the term "cultivar" arises from the need to distinguish between wild plants and those with characteristics that have arisen in cultivation (what we now call cultigens). This distinction dates back to the Greek philosopher Theophrastus (370–285 BCE), the "Father of Botany", who was keenly aware of this difference. Botanical historian Alan Morton notes that Theophrastus in his Enquiry into Plants"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).