Understanding Plant Nomenclature
Cerwin
Linnaeus created the current system of plant classification and naming
around 1753. He devised the binomial system of nomenclature (a system
of naming). This means that all plants have at least two names
attached to them - the genus and the species names. In addition, a
plant may also carry a variety or cultivar name or both.
This fact sheet describes how plants are named.
Genus
This term is used for a closely related and definable group of plants
consisting of one or more species. Classification is usually based on
similarities of flower and fruit but can include other plants as well.
The genus, Rosa, has between 100 to 200 species whereas the genus
Ginkgo has only one.
The genus name is always the first in the string of plant identifiers
and is therefore always capitalized and italicized as in Cornus.
Species
The term 'species' is generally thought to mean a kind of plant that
is distinct from others by a significant feature that has succeeded
through generations in an identifiable way. In practice, species are
difficult to categorize because, in nature, there is much variation in
patterns of growth.
A species name is always written in lower case and italicized
immediately following the genus name, as in Cornus florida.
Varieties (or Botanical varieties)
The term "variety" is used to describe a group or class of plants that
is subordinate to a species. This is a botanically recognized group.
It is usually used to describe naturally occurring variations, as seen
in nature that are inheritable by succeeding generations. Humans do
not create varieties.
Variety names are always written in lower case with the species as in
Cornus florida rubra or Cornus florida var. rubra.
Cultivars (cultivated variety) and groups
Cultivars and groups are sub-categories of plants that have been
created by humans and are recognized horticulturally. The term
'cultivar' is used to identify discrete populations bred by plant
breeders and maintained in cultivation, as opposed to plants that
occur and perpetuate themselves in the wild.
Cultivar names are written with single quotes around them. Each word
is capitalized but not italicized, as in Cornus florida rubra
'Cherokee Chief'.
According to the rules of the International Code of Nomenclature for
Cultivated Plants, cultivars named after 1959 cannot be given Latin-
form designations. They must have modern language names.
Plants that form part of a group are given a particular name that is
capitalized but not italicized and has no inverted commas, as in Fagus
sylvatica Purpurea.
Hybrids
Hybrids can occur in the wild or in cultivation. When two species
cross in nature or are crossed in a greenhouse, and the union results
in a distinct plant, it is called a hybrid. An 'x' in a plant name
signifies a hybrid. For example, Magnolia x loebneri, is a cross
between M. kobus and M. stellata, made, in this case, by the plant
breeder Max Loebner.
Synonyms
The word "synonym" or the abbreviation 'syn.' or the = sign means that
there is an old name for the plant that is no longer accepted. Plant
names are changed from time to time if they are proven botanically
imprecise or if a similar name is shown to already exist. Sophora
japonica, for instance, has recently been renamed because of recent
chromosome research and because the roots of true Sophora species
harbour nitrogen-fixing bacteria while those of S. japonica do not. It
is now called Styphnolobium japonicum.