Taxonomy is the science of classifying and naming living species. It plays an essential role in the study of biodiversity and in scientific communication. The following text provides an overview of how plants are named and classified.
Hierarchical categories
To organize and classify the roughly 375,000 known plant species, plant taxonomists have grouped them into hierarchical categories based on evolutionary relationships.
Species are grouped into genera, genera into families, families into orders, orders into classes, etc. There can be subdivisions within taxonomic ranks, such as subfamilies and subspecies.
Distinguishing between family, genus, and species
A family groups together plants that share morphological characteristics that are inherited from common plant ancestors. For example, all plants belonging to the Asteraceae family (sunflowers, daisies, dandelions, etc.) have a unique inflorescence with a flower head made up of many individual flowers often resembling a single flower, called a capitulum.
Within each family there are often several genera, and within each genus several species. A species includes plants that are similar in appearance, can reproduce with one another, and that distinguish themselves from other species by morphological and/or genetic differences.
When there are minor variations between individual plants or plants populations, the species can then be subdivided into subspecies, varieties, or forms.
Distinguishing between hybrids, varieties, and cultivars
Natural and artificial hybrids
Naturally occurring hybrid plants are the result of natural cross-pollination between two plants from different species, subspecies, varieties, or even genera.
Humans can also artificially create hybrid plants with unique and enhanced traits, such as:
- different colours
- extended flowering period
- increased productivity
- improved disease resistance
Did you know? Hybrids are not genetically modified organisms (GMO). Hybridization has always occurred in nature and artificial hybridization does not use genetic engineering techniques.
Distinguishing plant varieties from cultivars
It’s important not to confuse naturally occurring plant varieties with cultivars.
Plant varieties are the result of minor morphological variations within certain plant populations of a given species in its native range.
Cultivars are the result of human intervention through selection or artificial hybridization. For example, the “Celebrity” tomato is a cultivar that was created at the end of the 20th century by an American plant breeder.
The word “cultivar” comes from the contraction of the words “cultivated variety”.
Creating a universal system for naming species
In the 18th century, the Swedish botanist Carl Linnaeus suggested using two Latin terms to name all living organisms.
In this system, known as binomial nomenclature, the first name is the genus and the second is the specific epithet. Together, they form the name of the species. These two words are written in italics, with the genus being capitalized. For example, the red maple is called Acer rubrum.
In scientific texts, the name of the species is sometimes followed by the name (or an abbreviation of the name) of the first person to have described it (for example, L. for Linnaeus).
Why Latin?
Latin names, or scientific names, are universal, making it possible for everyone to understand one another regardless of spoken languages. Common or vernacular names, in contrast, vary depending on language and region.
Using Latin is also preferable because one species can be known under many common names. For example, the eastern red cedar (Juniperus virginiana) is also called red juniper, eastern juniper and Virignian juniper.
Conversely, one common name might be used to refer to several different species. For example, hemlock is often used to refer to poisonous plants in the Cicuta genus (such as water hemlock) as well as to the Tsuga genus of conifers (commonly called hemlock trees). Some species simply do not have any common names. Using Latin helps avoid confusion across the board.
Botanical nomenclature – key rules
There are many rules within the International Code of Nomenclature for algae, fungi and plants, including:
Common abbreviations
Scientific names often include abbreviations or letters. Here is what they stand for and how to use them correctly:
- The subspecies (subsp. or ssp.), the variety (var.) and the form (f.) are not italicized. Some examples are:
- Phragmites australis subsp. australis or Phragmites australis ssp. australis
- Viburnum opulus var. americanum
- Berberis tunbergii f. atropurpurea
- An “x” in a plant name means that the plant is a hybrid. For example:
- Iris x robusta (hybrid between Iris versicolor and Iris virginica)
- x Laeiliocattleya (hybrid between orchid genera Laelia and Cattleya)
- The abbreviations “sp.” and “spp.” are sometimes found following the name of a genus. The “sp.” abbreviation means species and desginates an unspecified species within a genus, whereas “spp.” refers to several or all of the species within a genus. Some examples are:
- Acer sp.: an unspecified species of maple
- Acer spp.: all species of maple.
- The abbreviation of the word cultivar is “cv.” (singular) or “cvs.” (plural). For example:
- Juniperus communis cv.: an unspecified cultivar of common juniper.
- Juniperus communis cvs.: several common juniper cultivars.
How to write cultivar names
The name of a cultivar is placed between single quotation marks and is not italicized (for example, Acer platanoides ‘Crimson King’). It should also not be in Latin. The only exceptions are old cultivar names that were already in use before this rule was applied, such as ‘Roseum’, ‘Flore Pleno’, ‘Grandiflora’, etc.
If there has been crosses between more than two species within a genus, the name of the cultivar may only appear next to a genus, such as Paeonia ‘May Apple’.
A cultivar’s name should never be translated. Its original spelling and language, be it French, English, German, etc., must remain as is. For example, the Bergenia ‘Silberlicht’ should not technically be sold as Bergenia ‘Silver Light’. That being said, many cultivars with foreign denominations end up being translated in the horticultural industry.
Naming plant families
In Latin, the suffix “aceae” is used at the end of plant family names, which are written in italics. For example, all roses belong to the Rosaceae family.
The old names for certain botanical families are still commonly used, such as Umbelliferaea (Apiaceae), Leguminosae (Fabaceae), Cruciferae (Brassicaceae), and Gramineae (Poaceae).
When plant names change
As science progresses, plant classification changes and it is relatively common for plant names to change. In these cases, the old name becomes a synonym, and may be added to the new name with the abbreviation “syn.”.
For example, Japanese knotweed could be written as:
Reynoutria japonica var. japonica, syn. Fallopia japonica
Feeling a bit overwhelmed? The rules of botanical taxonomy can seem confusing at first, but by naming and classifying plants in a precise and rigorous manner, plant taxonomists help expand our understanding of the incredible plant kingdom.