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How Plants Are Named

Taxon

Taxonomy is the science of plant classification. The word taxon (plural, taxa) refers to any taxonomic entity, regardless of rank. In other words, the plant family Ericaceae is a taxon, the genus Vaccinium is a taxon, and the species Vaccinium angustifolium is a taxon.

Genus and Species

The basic category of plants is the species. Every species on Earth has one, and only one, correct scientific name by which it is known throughout the world. This species name is called a binomial because, in fact, it is two words: the genus and the specific epithet. The binomial system we use today was founded by the Swedish botanist Linnaeus over 200 years ago. Because there has been a standard method of naming plants and rules for the creation and application of new names, we not only can communicate more effectively but also read works from Linnaeus's day and easily understand which species the author was referring to.

The following is the scientific name for the potato:

Solanum tuberosum Linnaeus

Solanum, the first part of the scientific name for potato, is the genus. It comes from the classical Latin name for this large and varied group that includes bittersweet, nightshade, potato, and Jerusalem cherry. In fact, the genus name is often based on the original Latin or Greek name for the plant. It also may be derived from a number of other sources, including the name of a botanist or an anagram. The name of the genus is written in italics.

The specific epithet is "tuberosum." It should almost always be in lower case; occasionally, if it is a proper noun (for example, someone's name), it can have an initial capital letter (this is optional under the code). The specific epithet is usually an adjective that modifies the genus. In this case, tuberosum indicates that potato is a tuberous species in the genus Solanum. Like the genus, the species is always written in italics.

"Linnaeus" refers to the author of the scientific name for potato. In other words, Linnaeus was the first person to use the binomial Solanum tuberosum for the potato plant. If the species were first classified in a different genus or at a different rank (if, for example, it were once considered a subspecies of another species) and was reclassified in its current genus and rank at a later time, the original author's name would be placed in parentheses, followed by the author of the current binomial. For example, Petroselinum crispum (Miller) A. W. Hill indicates that the botanist Philip Miller first named parsley using the epithet "crispum." Its original name was Apium crispum Miller. Later, this species was transferred by a botanist named Arthur Hill to the genus Petroselinum. In the interest of brevity, in many gardening books the author's name is omitted.

Subspecies, Variety, or Form

Often, a species exhibits some variation, such as different flower color, leaf shape, or height. If this variation is sufficient to warrant naming a new species, then a new species is named; but if the variation is minor or there is a broad range of overlap, a subspecies, variety, or form may be named. When one of these ranks is recognized, its name is formed by using the species name followed by "subsp.," "var.," or "f.," an additional epithet, and the name of the author of the subspecies, variety, or form. Which of these three ranks is used depends upon the type and magnitude of the differences between it and the other members of the species.

Subspecies is usually used to designate a group of populations that are approaching species status, and given time it is expected that the subspecies will evolve into a species. A subspecies is usually geographically distinct and has other characteristics that distinguish it from the species; however, the degree of separation is insufficient to call it a species. This is admittedly subjective and is one of the reasons why botanists change the names of plants. An alternative view held by many botanists is that subspecies is a rank between species and variety. In other words, subspecies are groups of varieties.

An example of a subspecies is

Chimaphila umbellata subsp. cisatlantica S. F. Blake

This is the scientific name for the eastern North American variant of pipsissewa. This plant is larger, with longer leaves and racemose inflorescences (the flower stalks occur along a branch), compared to the typical European subspecies, which has umbellate inflorescences (the flower stalks all come from a common point).

Variety has traditionally been used in the same manner as subspecies, to distinguish taxa that are approaching species but have not yet reached species status. Variety is also used to distinguish groups of populations with ecological differences. Variety and subspecies are often used interchangeably.

A form is usually used to designate a minor variation within a population or a region. For instance, albino forms of species are often designated as f. alba.

Cultivar

The names of cultivated variants are created in a similar manner. If a plant has been selected for some purpose-color, shape, growth characteristics, or other properties-and this selection can be propagated, it can be given a cultivar name. This name is created by taking the binomial species name and appending a non-Latin, non-italicized name placed in single quotation marks. (It is no longer acceptable to use "cv." before the cultivar name.) When a new cultivated plant is derived by hybridizing two species, the name is derived from the genus only, followed by the cultivar epithet in single quotes. Some examples include:

Clematis alpina 'Ruby'
Magnolia 'Elizabeth'

In other words, Clematis alpina 'Ruby' is a selection of the species Clematis alpina. Magnolia 'Elizabeth' is a magnolia hybrid resulting from the crossing of at least two Magnolia species.