Australian Cultivar Registration Authority Inc.
The cultivar is the basic grouping, or taxon (= culton), for cultivated varieties. The word was coined by L. H. Bailey in 1923 and is now commonly used. Their naming is governed by the International Code of Nomenclature for Cultivated Plants (ICNCP), the current version of which was published in 1995. A new version should be published very soon. This is a separate system to that used for wild plants, the International Code of Botanical Nomenclature (ICNB).
"By cultivated plants is meant plants raised in cultivation which differ sufficiently from their wild ancestors or, if taken into cultivation from the wild, are worthy enough of distinction from wild populations for horticultural purposes to merit special names"
W. T. Stearn (1986)
The rank of cultivar (ICNCP) is not the same as the categories variety or form in ICBN. A cultivar name can only be given to cultivated plants whose origin or selection is primarily due to the intentional actions of mankind. Normal forms of plants brought from the wild into cultivation retain the same name (ICBN) and similarly plant forms maintained solely by cultivation practices are not eligible for cultivar status. It is important to note that not all plants in cultivation are cultivars, and not all cultivars are in cultivation!
The equivalent of the ICBN type is the standard. This usually includes a herbarium specimen and a description. The standard may only be a description or illustration and in the case of grain crops it is usually just a sample of seed.
Plants that can be considered as cultivars include:
Hybrids, which are created sexually, can be either maintained asexually or by seed. F1 hybrids, which require to be re-created for each new generation, qualify as cultivars if the cross produces stable, repeatable forms.
Selections are usually asexually propagated (cloned) to maintain a particular plant form. Clones can be created in a variety of ways. For example, they may be taken from parts of the plant which result in a particular growth habit as when prostrate plants are derived from cuttings of lateral branches. Some clones maintain a particular phase of the plants life cycle. For example many Ficus cultivars are selected from forms of juvenile leaves that are maintained in a juvenile state. A common source of new cultivars is aberrant growth such as variegation of leaves.
To find out more about cultivars, visit the web site of the International Cultivar Registration Authority.