The basic unit of classification of all living organisms, including plants, is the species. The basis for naming all plant species, except mosses and some algae, is the book Species plantarum , written by the famous Swedish naturalist Carolus Linnaeus. This was the first consistent use of the system of binomial nomenclature, now recognized internationally. In this system, a plant (or animal) has two names; the first name designates the genus and the second the species.
The scientific nomenclature of plants is governed by precise rules. A plant is given a name and its appearance and characteristics are summed up by an apt description in Latin. The type is designated at the same time. This is the specimen possessing all the distinctive characters of the species used as the basis for comparison with other plants of the same species. Frequently, plants have been described more than once by different people and given a different name each time; such names are called synonyms (abbreviated ‘syn.’ in the text).
The names of hybrids may be designated in one of two ways. They may be given the names of the parent species in alphabetical order with an x between the names; for examplex . Alternatively, they may have a binomial designation with an x between the generic and specific name; for example, Fuchsia x hybrida. Some hybrids are designated only in the second of the two ways because it is not known which species figured in their parentage; for example x wittrockia-na. In the case of intergeneric hybrids an x is placed before the generic name, such as x , which is often formed by joining parts of the generic names of the parents, in this case, Fatsia and Hedera. In some instances species of the same genus are so interbred that they cannot be designated by a specific name. In this case, they are designated by the generic name plus the abbreviation for the word hybrid.
Decisions on the correct nomenclature of plants, not only of species, but of all levels of classification, from the lowest – form, variety, sub-species – to the highest – family, order, class, phylum, kingdom – are determined by the International Code of Botanical Nomenclature. However, the rules are not always observed in practice. For example a later but established synonym may be used as the valid name. There is no book in the world that could contain the truly’ correct name of plants, for the science of botany is continually developing, evaluations are changed by new discoveries and new species and hybrids continue to be described. Naturally the use of certain names is influenced most by widely circulated handbooks and compendiums.
The names of cultivars are additionally governed by the international code for cultivated plants. Cultivars are designated by the name of the ‘botanical’ species or hybrid, after which the abbreviation cv. (cultivar) appears. This is followed by the name of the cultivar written with an initial capital letter. Alternatively, the name of the cultivar is written simply in quotation marks.