A cultivar is a cultivated variety of a plant species. Modern cultivars are often, but not necessarily, hybrids between species; they may equally well represent particularly desirable selections from populations of a single species. Cultivars generally are identified by uniquely distinguishing names, which may be registered and trademarked. Names of cultivars are registered with an International Cultivar Registration Authority and conform to the rules of the ISHS Commission Nomenclature and Cultivar Registration. There are authorities for different plant-groups.
The word cultivar is a portmanteau coined from "cultivated" and "variety".
In botany a cultivar is indicated by using the abbreviation cv. and/or single-quoting the cultivar name. A cultivar may be ascribed to a particular species, or, if of hybrid or unknown origin, just to a genus. Cultivar names before 1 January 1959 were often given in Latin form and can be readily confused with names of botanical taxa, but after that date, must be in a modern vernacular language to distinguish them from botanical names. Cultivar names, unlike genus and species names, are not italicised. Thus:
Berberis thunbergii cv. 'Crimson Pygmy'
Cryptomeria japonica 'Elegans'
Rosa cv. Peace
Chamaecyparis lawsoniana 'Aureomarginata' (pre-1959 name)
Chamaecyparis lawsoniana 'Golden Wonder' (post-1959 name)
Natural and artificially pollinated hybrids are indicated with an x or multiplication symbol ×:
Berberis × frikartii.
Where several very similar cultivars exist, these may be termed Cultivar Groups; the name is in normal type and capitalised as in a single cultivar, but not in single quotes, and followed by "Group":
Brassica oleracea Capitata Group (the group of cultivars including all typical cabbages)
Brassica oleracea Botrytis Group (the group of cultivars including all typical cauliflowers)
Cultivars that are still being developed and not yet ready for release to seed companies often are coded with letters (signifying the university or other organization working on the variety) and numbers.
True cultural varieties
Some varieties are so well 'fixed' or established that they 'come true from seed,' meaning that the plants from a sowing will show very little variation. Such plants are better described by the more old-fashioned terms 'variety' 'selection' or 'strain,' and leaving the term 'cultivar' to plants that are vegetatively propagated ("cloned"), such as roses, Hemerocallis or iris.
Cultivars in natural settings
Many cultivars are "naturalized" in gardening, planted out and largely left to their own devices. With pollination and regrowth from seed, true natural processes, the distinct cultivars will over time disappear. The cultivar's genetic material however may become part of the gene pool of a population, where it will be swamped. This is why many trees are culled when a "back to nature" regime is in place.
Cultivars that have originated as hybrids of different species are exotic, as is a plant from a different continent. They are in itself a threat to the true type of a species.
With plants produced by genetic engineering becoming more and more widely introduced, it is important to note that the companies of these plants claim patent on their product. Therefore the notion that a plant that occurs from seed is natural is not appropriate any more.
- International Cultivar Registration Authorities (http://www.ishs.org/sci/icra.html)