A cultivar is a cultivated plant that has received a name under the International Code of Nomenclature for Cultivated Plants (the ICNCP, commonly known as the "Cultivated Plant Code"). For this, it must be distinct from other cultivars and it must be possible to propagate it reliably, in the manner prescribed for that particular cultivar. Status as a cultivar is a quite limited one, with nomenclatural consequences only; it offers no legal protection.
The word cultivar is a portmanteau coined by Liberty Hyde Bailey from "cultivated" and "variety" but is not interchangeable with the botanical rank of variety, nor with the legal term "plant variety".
Article 2.1 of the International Code of Nomenclature for Cultivated Plants states that a cultivar is the "primary category of cultivated plants whose nomenclature is governed by this Code." and defines a cultivar as "an assemblage of plants that has been selected for a particular attribute or combination of attributes, and that is clearly distinct, uniform and stable in its characteristics and that, when propagated by appropriate means, retains those characteristics" (Art. 2.2).
Nature of a cultivar
A cultivar is a particular variety of a plant species or hybrid that is being cultivated and/or is recognised as a cultivar under the ICNCP. The concept of cultivar is driven by pragmatism, and serves the practical needs of horticulture, agriculture, forestry, etc.
There is not necessarily a relationship between any cultivar and any particular genome. The ICNCP emphasizes that different cultivated plants may be accepted as different cultivars, even if they have the same genome, while cultivated plants with different genomes may be a single cultivar. In some cultivars, the human involvement was limited to making a selection among plants growing in the wild. Other cultivars are strictly artificial: the plants must be made anew every time, as in the case of an F1 hybrid between two plant lines. It is not required that a cultivar can reproduce itself. The "appropriate means of propagation" vary from cultivar to cultivar. This may range from propagation by seed which was the result of natural pollination to laboratory propagation. Many cultivars are clones propagated by cuttings, grafting, etc.
Cultivars are identified by uniquely distinguishing names. Names of cultivars are regulated by the International Code of Nomenclature for Cultivated Plants, are registered with an International Cultivar Registration Authority (ICRA) and conform to the rules of the ISHS (International Society for Horticultural Science) Commission for Nomenclature and Cultivar Registration. There are separate registration authorities for different plant-groups. In addition, cultivars may get a trademark name, protected by law (see Trade Designations and "Selling Names", below).
A cultivar name consists of a botanical name (of a genus, species, infraspecific taxon, interspecific hybrid or intergeneric hybrid) followed by a cultivar epithet. The cultivar epithet is capitalised and put between single quotes: preferably it should not be italicized. Cultivar epithets published before 1 January 1959 were often given a Latin form and can be readily confused with the specific epithets in botanical names: after that date, newly coined cultivar epithets must be in a modern vernacular language to distinguish them from botanical epithets.
- Cryptomeria japonica 'Elegans'
- Chamaecyparis lawsoniana 'Aureomarginata' (pre-1959 name, Latin in form)
- Chamaecyparis lawsoniana 'Golden Wonder' (post-1959 name, English language)
- Pinus densiflora 'Akebono' (post-1959 name, Japanese language)
- Some incorrect examples:
- Cryptomeria japonica "Elegans" (double quotes are unacceptable)
- Berberis thunbergii cv. 'Crimson Pygmy' (this once-common usage is now unacceptable, as it is no longer correct to use "cv." in this context; Berberis thunbergii 'Crimson Pygmy' is correct)
- Rosa cv. 'Peace' (this is now incorrect for two reasons: firstly, the use of "cv."; secondly, "Peace" is a trade designation or "selling name" for the cultivar R. 'Madame A. Meilland' and should therefore be printed in a different typeface from the rest of the name, without any quote marks, for example: Rosa Peace.)
Where several very similar cultivars exist, these are 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" (or its equivalent in other languages)
- Brassica oleracea Capitata Group (the group of cultivars including all typical cabbages)
- Brassica oleracea Botrytis Group (the group of cultivars including all typical cauliflowers)
- Hydrangea macrophylla Groupe Hortensis (in French) = Hydrangea macrophylla Hortensia Group (in English)
Where cited with a cultivar name the Cultivar Group should be enclosed in parentheses, as follows:
- Hydrangea macrophylla (Hortensia Group) 'Ayesha'
Some cultivars and Cultivar Groups are so well "fixed" or established that they "come true from seed", meaning that the plants from a seed sowing (rather than vegetatively propagated) will show very little variation. In the past, such plants were often called by the terms "variety", "selection" or "strain"; these terms (particularly "variety", which has a very different botanical meaning – see below) are best avoided with cultivated plants. Normally, however, plants grown from seed taken from a cultivar can be very variable and such seeds or seedling plants should never be labelled with, or sold under, the parent cultivar's name (See  an article by Tony Lord of The RHS Plant Finder).
Trade designations and "selling names"
Cultivars that are still being developed and not yet ready for release to retail sale are often coded with letters and/or numbers before being assigned a name. It is common for this code name to be quoted alongside the new cultivar name or trade designation when the plant is made available commercially (for example Rosa Fascination = 'Poulmax') and this may continue, in books or magazines and on plant labels, for several years after the plant was released. Because a name that is attractive in one language may have less appeal in another country, a plant may be given different selling names from country to country. Quoting the code allows the correct identification of cultivars around the world and helps to avoid the once-common situation where the same plant might, confusingly, be sold under several different names in one country, having been imported under different aliases.
Cultivars in the natural world
Some cultivars are "naturalized" in gardening, in other words they are planted out and largely left to their own devices. With pollination and regrowth from seed, true natural processes, the distinct cultivars will disappear over time. The cultivar's genetic material however may become part of the gene pool of a population, where it will be largely but not completely swamped.
The practice of patenting, (or legally protecting) living plants is considered unethical by some people. To most is considered an essential tool to encourage the developement of new useful cultivars. "Cultivars" are the result of deliberate breeding programand selection activity by nurserymen or plant breeders and are often the result of years of dedicated work involving painstaking trialling and selection. "Plant patents" and "plant breeder' rights" (which is itself expensive to obtain) allows the inventor to obtain some financial reward for their work, normally for a limited period and geographical area.
With plants produced by genetic engineering becoming more and more widely used, it is important to note that the companies producing these plants (or plants produced by traditional means) often claim a patent on their product. Thus the notion that "letting seed germinate and grow into a crop is the most natural thing in the world" is no longer appropriate; it can be illegal to harvest seeds (even in one's own fields) from a patented "variety" (which may or may not also be a cultivar) except for personal use. Such plants are often labelled "PBR", which stands for "plant breeders' rights", or "PVR", which stands for "plant variety rights").
- Sale point of the Latest Edition (February 2004) of The International Code of Nomenclature for Cultivated Plants
- International Cultivar Registration Authorities
- The Language of Horticulture
- Opinion piece by Tony Lord (from The Plantsman magazine)
- HORTIVAR - The FAO Horticulture Cultivars Performance Database