T1.5 Cultivars and Clones
name - species - subspecies - cultivars - hybrids - common names
A cultivar may be defined as ‘‘an internationally agreed term for a cultivated variety’’ and a clone as ‘‘genetically uniform group of plants originating from a single plant by vegetative propagation.’’
A variety within a species is usually identified form the typical form by botanical characteristics which may or may not be relevant to its selection and use within horticulture or landscape work. A cultivar is a plant which has been specifically selected by man because it exhibits different characteristics from the typical species and is worth maintaining in cultivation by vegetative propagation or by seed in the case of true breeding cultivars. Acer platanoides ‘Crimson King’ is a cultivar of Acer platanoides the Norway Maple selected and cultivated for its deep purple leaves. In this instance the change in leaf colour arose by chance and it is easier to maintain in cultivation by vegetative means than relying on seed. Clones are the vegetatively produced offspring from a single parent and are, therefore identical to the parent in all respects. Many cultivars are, in fact, clones, propagated vegetatively in order to perpetuate the characteristics of the original selection.
In the example above, Acer platanoides ‘Crimson King’ is exactly like the green leafed Acer platanoides except for its leaf colour. It is not, therefore, difficult to identify that it is a variation of a particular species and the cultivar name qualifies the species name. However, through selection, hybridisation and mutation, it is not always easy to link a cultivar name to a species or hybrid. An example is Prunus ‘Snow Goose’. Its exact botanical origins are in doubt but it is a cultivar within the genus Prunus which has been selected and continues to be propagated. In these instances the species name is left out.
Cultivars are common in commercial and amenity horticulture. Whilst the genus, species and variety is identified by the use of italic type face and the use of a combination of upper and lower case letters, cultivar names are in Roman letters, with an upper case initial and is within single inverted commas.
e.g. Fraxinus excelsior ‘‘Westhof’s Glorie’ or Sorbus ‘Sheerwater Seedling’