How are Plants Named?

History of organized nomenclature

Linnaeus (1707‑1778) was a Swedish botanist, largely responsible for establishing the binomial system (i.e.: using two names or two words to name one plant).  He was also responsible for stabilising some of the other basic principles of nomenclature. 

It wasn't however until 1867 though, at the first International Botanical Congress, that the first set of rules was officially adopted by the botanical world.

Deficiencies in this code led to the establishment of a number of other sets of rules.

A compromise between the existing codes was adopted in 1930 and published as the 3rd edition of the International Rules of Botanical Nomenclature.  More recent editions are basically modifications of this code.

International Code of Botanical Nomenclature

Published in 1966, this most recent edition of the code contains an enormous amount of detail which is only of any real interest to the specialist, however, some of the <st1:st1:personname w:st="on">information from the code outlined below is valuable in helping us understand better the way in which plants are classified.

Ranks of Taxa

The code indicates the ranks (i.e. : levels of classification) of taxa which can be used, and specifies the order in which they must be placed.  In all, there are 23 ranks listed and provision is made for supplementary ranks.  It isn't necessary to use all ranks for a particular organism.  In day to day use, the genus and species are the two ranks which are commonly used.  The endings of names of taxa of some ranks are standardised (i.e. : Names of the rank of family end in 'aceae' ...e.g.: Rosaceae).  The most commonly used ranks are listed below, in order and with examples:

Division ‑ Spermophyta

   Class  ‑  Angiospermae

      Order  ‑  Rosales

         Family  ‑  Rosaceae

            Genus  ‑  Prunus

               Species  ‑  persiecae

                  Variety  ‑  versicolour

Principle of Priority

This provision means that a plant can bear only one legitimate name and two different plants cannot be called by the same name.  The legitimate name of a plant is the one published first, in or after 1753, in accordance with the code.

a)  <st1:st1:personname w:st="on">Valid Publication

To be validly published the name must be published in a suitable book or journal accompanied by a description or diagnosis of it's ranks stating in detail the characteristics which distinguish it from others.

b)  The Type Method

For species categories or anything below that level of classification, a specimen must be nominated as the type (an example of that classification) and deposited in a herbarium.  (Herbariums store collections of pressed plants as a reference point; usually government sponsored and often associated with botanical gardens).  The type provides a permanent record of the kind of plant which is associated with that particular classification.

Under certain circumstances, a photo may be acceptable as a type.

c)  Aim of the Principle of Priority

The aim of the principle is to stabilise nomenclature when two or more names are inadvertently coined for the same taxon.  (i.e.: for the same type of plant) 

The one which was published first takes that name and the other must be renamed.

d)  Exceptions to the Principle of Priority

Occasionally even if published validly, names have to be rejected in certain prescribed circumstances e.g.: if the same name is published for two different genera or families.  Sometimes names are 'conserved' (i.e. remain valid) though they were not the first published of two contending names.  This is usually because they have been more commonly used than the earlier name.  (e.g.: Melaleuca (1767) is conserved against Cajaputi (1763)).

Plant and Animal Nomenclature

Plant nomenclature is independent of animal nomenclature.  It does no matter if the name of a plant is the same as an animal, though it is better to be avoided if possible.

Choice, Construction and Spelling of Names

Botanical names are Latin and are treated as such, the code being very precise on matters of grammar. 

‑Names of orders and sub orders are based on the stem of the name of a family from that particular order or sub order with the ending "ales" for orders and "ineae" for the sub orders.  There are only a few exceptions.  e.g. Order Proteales (from family Proteaceae)  Usually the names of families, sub families, tribes and sub tribes are formed by adding a specified suffix to the stem.

‑The name of a genus is a noun (or sometimes an adjective) which can usually be taken from any source.

‑The name of a species is a binomial i.e.: it consists of two words, the first being the generic name and the second a specific epithet (name).  The specific epithet may be taken from any source, and often describes a particular characteristic about the species (e.g.: spinose‑spiny, paludosus ‑growing in swampy places, citriodora ‑ lemon scented, rubra‑red, pendular‑ weeping, palmatum‑palm like etc.)

‑The main categories or divisions below species are:‑

subspecies (which are divided into varieties)

varieties (which are divided into forms).

Changes in Names

Provided there is good reason it is possible to change names.  For example, if a genus is considered to be in the wrong family or a species in the wrong genus it can be transferred to the correct one.  Sometimes it might be decided that one genus should be divided to make two or three genera.  The code governs the way in which such things happen (e.g. if a genus is split then the original name must be retained for at least one of the new genera.

Nomenclature of Hybrids

The names of hybrids (different species which have cross bred) are governed by the same rules as the names of other taxa.  The hybrid is designated by the use of a multiplication sign preceding a given name (e.g.: Salix X capreola which is a hybrid of Salix aurita and Salix caprea) or by a formula (e.g.: Salix aurita X caprea).

Abbreviations

( )  Indicates the original authority for a name.

e.g.:  Medicago arabica (l) Huds.

This means it was originally names by Linnaeas but the name was changed by <st1:st1:place w:st="on"><st1:st1:city w:st="on">Hudson later.

nom cons. Indicates the name was conserved against some earlier published name.

e.g.:  Olearia Moench, nom. cons.

Means Olearia was conserved against the generic name Shawia which was validly published at an earlier date.

nov. Indicates new taxon.

syn. Indicates a synonymous name.

nov. syn. Used when a name is first reduced to synonymy.

There are many other abbreviations.  You do not need to learn these for this subject, but it is of value to know that there is meaning behind them when you do come across them in books.