Nomenclature

The naming of cultivated plants
The binomial system
The name given to a plant species is very important. It is the key to identification in the field or garden, and also an international form of identity, which can lead to much information from books and the Internet. The common names which we use for plants, such as potato and lettuce, are, of course, acceptable in English, but are not universally used. A scientific method of naming can also provide more information about a species, such as its relationship with other species.

Linnaeus, working on classification and with the more detailed question of naming, formulated a system that he claimed should identify an individual plant type uniquely, by means of the composed genus name followed by the species name. For example, the chrysanthemum used for cut flowers is Chrysanthemum genus and morifolium species; note that the genus name begins with a capital letter, while the species has a small letter. Other examples are Ilex aquifolium (holly), Magnolia stellata (star-magnolia), Ribes sangui-neum (redcurrant).

Subspecies can evolve and display more distinct characteristics than the varieties detailed below, e.g. Rhododendron arboreum subsp. cinnamomeum. The genus and species names must be written in italics, or underlined where this is not possible, to indicate that they are internationally accepted terms. However, these two words may not encompass all possible variations, since a species can give rise to a number of naturally occurring varieties with distinctive characteristics. In addition, cultivation, selection and breeding have produced variation in species referred to as cultivated varieties or cultivars.
The two terms, variety and cultivar are exactly equivalent, but the botanical variety name is referred to in Latin, beginning with a small letter, e.g. Rhododendron arboreum var roseum, while the cultivar is given a name often relating to the plant breeder who produced it, e.g. Rhododendron arboreum 'Tony Schilling'. There is no other significant difference in the use of the two terms, and therefore either is acceptable. However, the term cultivar will be used throughout this text. A cultivar name should be written in inverted commas and begin with a capital letter, after the binomial name or, when applicable, the common name. Examples include: Prunus padus 'Grandiflora', tomato 'Ailsa Craig', apple 'Bramley’s seedling'.

If a cultivar name has more than one acceptable alternative, they are said to be synonyms (sometimes written syn.) e.g. Phlox paniculata ‘Frau Alfred von Mauthner' syn. P. paniculata 'Spitfire'.

Hybrids
When cross-pollination occurs between two plants, hybridization results, and the offspring usually bear characteristics distinct from either parent. Hybridization can occur between different cultivars within a species, sometimes resulting in a new and distinctive cultivar, or between two species, resulting in an interspecific hybrid, e.g. Prunus × yedoensis and Erica × darleyensis. A much rarer hybridization between two different genera results in an intergeneric hybrid, e.g. × Cupressocyparis leylandii and × Fatshedera lizei. The names of the resulting hybrid types include elements from the names of the parents, connected or preceded by a multiplication sign (×). A chimaera, consisting of tissue from two distinct parents, is indicated by a 'plus' sign, e.g. + Laburnocystisus adamii, the result of a graft.