What’s in a name?
Summary
All living organisms on the planet are classified using a hierarchical taxonomy originally set out by Carl Linnaeus. The two most important levels of this taxonomy are the genus and the species. Species are named using binomial nomenclature: a generic name (the genus) and a specific epithet (identifying the species within the genus). Plant species are named using Botanical Latin. Binomial names are used instead of common names to avoid confusion across different countries and across different plants with the same common name.
There are close to 400,000 species of plants. Attempting to understand the nature and properties of each individually would be a colossal, and perhaps foolhardy, undertaking - an in depth study of just one species could be the work of a lifetime for a botanist, and it would be impossible to apply this knowledge to other plants. Fortunately, there are many common features and characteristics amongst different plants, since the huge diversity present today evolved over millennia from a much smaller number of progenitors.
To bring order to this chaos, biologists (and particularly Carl Linnaeus, a Swedish biologist whose image graces this blog post) developed a systematic approach to naming organisms, using a hierarchy of classifications (the “Linnaean taxonomy”). At the top level of this hierarchy, the diversity of organisms on Earth (not just plants) is divided into three “domains”: the Archaea, Bacteria and Eukarya - the latter containing all animals, plants, fungi and many single-celled lifeforms (and despite this, representing only a small minority of the total number of organisms on the planet). Each domain is then further subdivided into “kingdoms”; each kingdom into “phyla” (singular “phylum”); and so on through “class”, “order”, “family”, “genus” and “species”.
The full Linnaean taxonomic classification of the Asphodel (Asphodelus albus)
These groupings were originally determined based on similarities in appearance, structure and behaviour. With the powerful scientific tools at their disposal, modern geneticists no longer use the Linnaean taxonomy, instead using genetic analysis to group organisms based on their most recent common ancestry (an approach known as “cladistics”). However, other scientists, not to mention horticulturalists, continue to use the simpler approach described here; with new genetic discoveries resulting in reclassification of organisms from time to time (this is why Michaelmas daisies used to have the genus Aster, and now are known as Symphyotrichum, for example).
Further subdivisions
Whilst classification to the level of species is usually sufficient for most scientific purposes, for agriculture and horticulture, it is often necessary to consider yet more precise divisions: “subspecies” and “varieties”. A subspecies is a population of a species that lives in a different area, and varies in size, shape or other physical characteristics (“morphologial characteristics”). A variety is distinguished from a subspecies in that it does not refer to geographic distinctiveness, only to morphological characteristics. The geographical isolation of two separate subspecies means that they do not naturally interbreed (though can be deliberately crossed to produce fertile offspring, unlike two separate species); distinct varieties of a species will hybridise freely. A further rank, “form”, is sometimes uses to describe minor variations within a species, subspecies or variety.
Plant breeders deliberately cross different parents plants to select desired morphological characteristics, notably including resistance to particular pests or pathogens. The offspring are not naturally occurring varieties, so are known as “cultivars” (cultivated varieties).
As an example of the importance of subspecies and varieties in agriculture, Daucus carota var. sativa, commonly known as the carrot, is an important food crop. The overall species, Daucus carota, includes the wild carrot, which although edible, is tough and difficult to chew, and lacks the sweetness of its agricultural cousin. Different cultivars of carrots have different commercially important characteristics, so for example Daucus carota ‘Chantenay’ has a short stubby form, and Daucus carota ‘Bolero’ not only stores particularly well once harvested, but is resistant to blight and powdery mildew.
Breeders may also deliberately cross two different species to form an “interspecific hybrid”, or more rarely, two plants of different, but closely related genera to form an “intergeneric hybrid”.
Binomial nomenclature and Botanical Latin
The lowest level of the Linnaean taxonomy (but not the lowest level for horticulturalists, see below) is the species, and the next highest, the genus. Together, these are usually sufficient to avoid any confusion as to which organism is being discussed, without including higher levels of the taxonomy. As a result (and as originally set out by Linnaeus), species are given a two part name, consisting of a “generic name” (the genus to which the species belongs) and a “specific epithet” (distinguishing the species within the genus). Our namesake flower, the asphodel is in the genus Asphodelus and has the specific epithet albus, giving it its “binomial name”, Asphodelus albus. To avoid confusion, the generic name is always capitalised, and the specific epithet always written in lower case; and in print both are italicised (underlined when written by hand).
The names of genera (plural of genus) and species of plants are always written in “Botanical Latin”. This is something of a misnomer, as many of the words used are derived from non-Latin languages: some based on the language of the country in which the species was discovered; some based on the name of the discoverer; some based on historic common names for the plant; and some for no apparent reason! Botanical Latin is a written only language - there is no standard pronunciation of the words used, and hence no right or wrong way of saying them.
Subspecies, varieties, and forms are written using the abbreviations “subsp.”, “var.”, and “f.” respectively (neither is italicised), followed by the subspecies or variety name (in italics). Cultivars are written with the name in single inverted quotes, always capitalised but never italicised. Interspecific hybrids are identified by a cross, “x”, between the generic name and specific epithet, and intergeneric hybrids by a cross before the generic name. So for example:
Hydrangea anomala subsp. petiolaris (climbing hydrangea)
Acer palmatum var. atropurpureum (purple-leaved Japanese maple)
Viburnum plicatum f. tomentosum (doublefile viburnum)
Cryptomeria japonica ‘Elegans’ (the ‘Elegans’ cultivar of Japanese cedar)
Malus x domestica ‘Granny Smith’ (Granny Smith apple)
X Cuprocyparis leylandii (Leyland cypress)
Binomial names and common names
Many plants have been known for centuries, and have common names that are well understood, and often cherished, within a particular society. These names often evoke cultural associations, and are more familiar than the often sterile-sounding binomial names. For example, “Lady’s mantle” is more evocative than Alchemilla mollis. So why then should we use binomial names rather than common names.
The answer is simple; to avoid confusion and ensure that we are always referring to the same plant.
A single plant species may have different common names in different cultures. Caltha palustris is known to Americans as the “marsh marigold”, and to Britons as "the “kingcup”. And of course common names vary in different languages: Bellis perennis, the daisy, is known in French as “la marguerite”.
Perhaps worse, the same common name may be used to refer to different species. Borrowing an example I found online (here), all of the following species share the common name “Wandering Jew”:
Tradescantia fluminensis
Tradescantia pallida
Tradescantia zebrina
Commelina africana
Commelina benghalensis
Commelina cyanea
Commelina ensifolia
Saxifraga stolonifera
Tinantia pringlei
Furthermore, the common name of a plant may mislead as to the nature of that plant. “Heavenly bamboo” (Nandina domestica) is not a bamboo (a bamboo is a type of grass and is a monocot - don’t worry if this term isn’t familiar - whereas Nandina domestica is a type of barberry and is a eudicot). Asparagus ferns” are not ferns (true ferns are not flowering plants, unlike the asparagus fern; and since the term “asparagus fern” refers to more than one plant, I can’t even give a binomial name).
Using binomial names in Botanical Latin allows scientists, botanists, horticulturalists, plant breeders, gardeners and many others to know with certainty that they are referring to the same plant. The names may be unfamiliar, but they are no more difficult to learn than many of the common names we may be familiar with.