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Plant nomenclature

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Chrysanthemum.
Photo: Jardin botanique de Montréal (Gilles Murray)

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With just a few exceptions, most Chrysanthemum were reassigned to Dendranthema, or Arctanthemum, or Leucanthemum?

In the end, botanists reversed their decision and then gave the florist’s chrysanthemum back its old genus name of Chrysanthemum, but changed the epithet from x morifolium to x grandiflorum.

Welcome to the wonderful world of taxonomy (from the Greek taxis, for “arrangement”, and nomos, for “method”), the science of classifying biological organisms, which uses systems, codes and rules for coming to an understanding on plants.

Latin nomenclature

Since Linnaeus and the first edition of Species Plantarum in 1753, a plant’s scientific name has always consisted of at least two words: the genus and the species, both in Latin. Although this dead language has little interest for the vast majority of people, it gives scientific communications an essential neutrality.

But that doesn’t make it simple. To properly arrange the some 250,000 natural species, taxonomists have grouped genera into families, families into orders, and so on, and allowed species to be subdivided into subspecies, varieties and forms. All together, this is called a classification system.

The division into families, genera and species is based on evolutionary theory, which explains how complex heredity and mutation phenomena occur.

A family contains a number of individuals that share certain genes and features, because they are all descended from the same parents. A family usually includes several genera, which themselves include several species.

Since there are many taxonomists, there are several classification systems. This can sometimes lead to confusion when it comes to families: for instance, some people consider that Fabaceae, Cesalpinaceae and Mimosaceae are very distinct families, while others simply group them into subfamilies in a single family, i.e. Fabaceae (or Legumes).

Another source of confusion is that some plants may have been named and described twice, or the wrong name may be mistakenly attributed to a plant year after year.

Moreover, after detailed studies, a genus may be subdivided into several genera, or a subspecies may be promoted to a species. In that case, sometimes well-known names have to be changed – which naturally leads to much confusion and frustration. The former names then become synonyms, and appear after the valid name, e.g. Chrysanthemum x grandiflorum (= Chrysanthemum x morifolium).

Up until 2003, the Montréal Botanical Garden used the system devised by the Russian taxonomist A. Takhtajan. Since then, because it is managing its collections inventory with a computer application called BG-BASE, the Garden has adopted the system developed by Brummitt, at the Royal Botanic Gardens, Kew.

The rules of botanical nomenclature are established at international congresses held every six years. The first of these was held in Paris, in 1867. Each congress adopts revisions to the International Code of Nomenclature for Cultivated Plants, a sort of taxonomist’s bible.

Horticultural nomenclature

By cross-breeding species or individuals of the same species, human beings obtained cultivated varieties, called “cultivars.”  

Since January 1, 1959, the cultivar name has no longer been in Latin, like the old ‘Roseum’, ‘Flore Pleno’, ‘Grandiflora’, etc. In addition, it must retain its original form. In other words, Bergenia ‘Silberlicht’ is not to be sold as Bergenia ‘Silver Light’. Another subject that leads to confusion is the fact that hybrids between two species may be registered under a cultivar name (Paeonia ‘May Apple’: note the lack of the species name) or under a new species name (Lilium x hollandicum).

Vernacular nomenclature

Most common names are based on folklore, convey local colour and are generally evocative. They are easy ways for people to remember plant names.

A problem with common names is that there are sometimes none, or too many. Remember that a plant will be given a common name if it is part of people’s daily lives. So a well-known plant in China will probably have a vernacular name in Chinese, but not in English or French.

Along the same lines, a plant that is neither ornamental nor economic may not have a common name at all. Other plants, however, have a multitude of common names. Arctium minus, for example, is also known as lesser burdock, burweed, louse-bur, common burdock, button-bur, cuckoo-button, and wild rhubarb. Lastly, the anglicized version of the Latin name is simply used as the common name for many highly ornamental plants such as begonias, irises, and so on.

Rules

In the jungle of nomenclature, there are a few rules for survival. Cautiously trust Latin names, be wary of all “varieties,” be wary of all traditional and made-up common names, and, as a last resort, consult your taxonomist, or at the very least the sources he or she considers trustworthy.

Terminology

Botanical terms can certainly cause confusion! However, because there are more than 600,000 species of plants, according to some experts, a classification system was desperately needed in order to tell one from another! Classification by family, genus and species is based on the theory of evolution through which complex phenomena of heredity and mutations present themselves.

A family is composed of individuals with common traits and genes, as they all come from the same parents. A family generally comprises several genera, which in turn comprise several species. Each plant has a genus and a species in accordance with Linneus’ system of binomial nomenclature. A species is defined as a group of plants that descend from a common ancestor and can reproduce with one another, but generally not with the members of another species. The characteristics unique to the species are reproduced through their seeds from one generation to another. A variety is an individual plant within a species that is different from other members of the species. The characteristics that make this plant different can be reproduced through its seeds from one generation to another.

Based on an article by Édith Morin in Quatre-Temps magazine and subsequently updated.

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