Plant Nomenclature Syntax

By Mike Short, 2024-12-26

There is a printable version at Plant-Nomenclature-Syntax.pdf

A layman’s shot at demystifying the Latin naming conventions used in botany. The author is not a botanical expert, and does not have any botanical qualifications. What follows is information put together from the web and from books. The definitions below are by no means incontrovertible and may be over-simplified.

Nomenclature vs Taxonomy … my interpretation is that Nomenclature refers to the structure and syntax of scientific names whereas Taxonomy is what the government takes out of my pay packet, no seriously it refers to the actual names of plants and takes into account their place in the schema of life.
Nomenclature is clearly specified, but taxonomy is constantly changing as plants are being re-categorized regularly due in part to modern techniques of molecular DNA analysis.

CONTENTS

OVERVIEW

The system of binomial nomenclature that is in use today was started by Carl Linnaeus in 1753 with his book Species Plantarum.

It is now governed by the International Association for Plant Taxonomy (IAPT) who administer the International Code of Nomenclature for algae, fungi, and plants (ICN).

The naming of cultivars is governed by the International Society for Horticultural Science (ISHS) who administer the International Code of Nomenclature for Cultivated Plants (ICNCP). A “cultivar” is defined as a plant whose origin or selection is primarily due to intentional human activity.

The term “binomial” indicates that there were originally two words (in Latin) to describe a species, however many have extra words to describe their divergence from the base species giving rise to the term “trinomial”. These extra (infra-specific) terms include variety, form, and cultivar and are used to differentiate species while maintaining the relationship between species.

A better term for the complete name is the “taxonomic name”, abbreviated as “taxon”, plural “taxa”.

Taxa are considered to be organized in a hierarchical system of rank where the highest rank is all inclusive and the lowest rank is a single organism. All plants are under the kingdom called Plantae, the major ranks being:

There are more ranks and subdivisions of rank that are defined, also defined are clade and strain, see the section RANK below. However the main focus of this document is on genus and ranks below along with their subdivisions, in order of rank:
   genus > species > variety > form.

A common source of confusion is that the word “species” is often used to refer to the second word of a taxon. However the technically correct usage is that the species is the combination of the first two words, although it is more commonly used to describe the full taxonomic name.

For example for the plant Aloe vera it is often said that the genus is Aloe and the species is vera, however the correct usage is that the species is Aloe vera, the word vera being the “epithet” (a.k.a. specific epithet).

This document will use the term “epithet” for the second word to avoid confusion.

There are several dictionary definitions of the word species, the Cambridge Dictionary uses “a set of animals or plants in which the members have similar characteristics to each other and can breed with each other”.

TAXON EXAMPLE 1

DEFINITIONS

Genus

(plural: genera, abbreviation: gen.):
A subdivision of Family (example Cactaceae) including plants of similar nature especially in their sexual characteristics. The genus name forms the first part of the binomial species name for each species within the genus. Examples: Agapanthus, Sedum.

Subgenus

(plural: subgenera, abbreviation: subg.):
Rarely used, can be used to separate plants within a genus that will eventually be moved to another new genus.

Epithet

Also known as the Specific Epithet, Specific Name, or just Species.
“The major subdivision of a genus, regarded as the basic category of biological classification, composed of related individuals that resemble one another, are able to breed among themselves, but are not (usually) able to breed with members of another species”.

The epithet is the second word of a taxon. When the genus is known but the species is not the abbreviation sp. is often used, ex: Aloe sp.

Connecting Terms:

In botany when a taxon has more parts than the two binomial ones, Genus and Epithet, a connecting term is used that indicates the rank of the following words. Also known as the “Taxon Rank” in some publications, not to be confused with the general term “Rank” see below.

These 6 are the most commonly used in order of rank (see below for rare connecting terms):

Note that in zoology there is only one rank, subspecies, so connecting terms are not used.

Rare Connecting Terms

In addition to the common connecting terms mentioned above there are these less common ones:
‘agamosp.’, ‘convar.’, ‘ecas.’, ‘group’, ‘lusus’, ‘microf.’, ‘microgene’, ‘micromorphe’, ‘modif.’, ‘monstr.’, ‘mut.’, ‘nid’, ‘nothof.’, ‘nothosubsp.’, ‘nothovar.’, ‘positio’, ‘proles’, ‘prole’, ‘prol.’, ‘provar.’, ‘psp.’, ‘sect.’, ‘ser.’, ‘stirps’, ‘subgen’, ‘sublusus’, ‘subproles’, ‘subsect.’, ‘subser.’, ‘subspecioid’.

Infraspecific Epithet

The part of a taxon following a connecting term. A taxon with one is known as an infraspecies, the full name may be termed the infraspecific name. Example “Aloe officinalis var. angustifolia” where angustifolia is the infraspecific epithet.

Unfortunately it’s common to see the specific epithet omitted when there is also an infraspecific epithet, this is not good practice because the infraspecific epithet may not be unique among the genus. For example “Euphorbia polygona var. minor” might be written as simply “Euphorbia minor” but that could also refer to “Euphorbia lydenburgensis var. minor“.

Cultivar

(Enclosed in single quotes, see SYNTAX below. Historically cv. which is now deprecated)
A variation of a species, subspecies, or variety, being created by man and not found in nature.

They can be created by means that include, selection, cross-pollination, and various forms of hybridization.

A cultivar name is written between single quotes, for example Aeonium ‘Sunburst’ or Crassula ‘Tom Thumb’. The general rule is that names are English (not Latin) and each word is capitalized except for conjunctions like ‘and’ and ‘or’.

Cultivars are given names by the growers that create them but those names are not accepted as species by authorities like IPNI (International Plant Names Index) or WCVP (World Checklist of Vascular Plants).

Cultivar names are random in that they are not related to the genetics of a plant but often describe some feature of a plant, like ‘Black and Blue’ or ‘Gollum’.

Cultivar Registration:

Cultivars are considered to be the “Intellectual Property” of the creator and the names can be registered with the International Society for Horticultural Science (ISHS) to avoid duplication. The ISHS appoints a number of International Cultivar Registration Authorities (ICRAs) each covering a group of genera. A list of the many current authorities is at the Directory of ICRAs.

Many cultivars are of food crops and are important financially to the creator. However many (maybe most) cultivar names are not registered and, although popularly known, cannot be considered official.

Hybrid

(abbreviated ×, unicode 00D7, see SYNTAX below for more)
A crossbreed between two species, subspecies, varieties, or occasionally genera.
They can exist in nature but most are man-made. Many man-made hybrids are given cultivar names and lose the record of their parentage.

Grex

(plural greges or grexes; abbreviation gx)
Derived from the Latin noun grex, gregis, meaning ‘flock’, used in botanical nomenclature to describe hybrids of orchids, based solely on their parentage. Grex names are governed by the International Code of Nomenclature for Cultivated Plants.

TAXON EXAMPLE 2

SYNTAX

Syntax is important for effective communication, including the case and slant of any text. The rules below are applied to the full names of species, but are optional when only referring to a part of a name, like the genus.

Genus

Names are written in italics (or underlined), the first letter is capitalized, ex: Juniperus.

Subgenus

If present is used instead of Genus using the same syntax.

(Specific) Epithet and Infraspecific Epithet

Names are written in italics (or underlined) all lowercase, ex: ovata. An epithet can consist of two names which must be hyphenated, ex: castello-paivae.

Connecting Term

(subsp., var., f., etc.) are lowercase. The abbreviation is preferred over the full term, and the dot is always included. They are not written in italics, ex: Crassula arborescens subsp. undulatifolia.

Cultivar

Names are written between single quotes. The quotes can be either:

Even Grave Accent (`  unicode 0060) and Acute Accent (´  unicode 00B4) are accepted.

Each word is capitalized (except words like and), examples ‘Blue Flame’, ‘Black and Blue’.

Note that single quotes can create problems on computers, especially when the name contains one, using curly quotes with an apostrophe inside the name is a solution ex: ‘Hummel’s Sunset’, or the other way round with curly one inside straight ones, ex: ‘Hummel’s Sunset’ (can you spot the difference?).
Also note that many word processors will insert curly quotes when apostrophe is tapped on the keyboard.

Hybrid

Names use the symbol for the multiplication sign (×), unicode 00D7, although if the multiplication sign is not available it can be approximated by the lower-case letter “x” (not italicized).

There are three ways of writing hybrids:

When a hybrid has a parent with infraspecific information the prefix “notho” may be used with the connecting term making nothof, nothosubsp, and nothovar, ex: Aloe ciliaris nothovar. gigas. It is possible to denote an F2 hybrid by doubling the multiply signs, ex: Anacamptis × × olida nothosubsp. olida.

WORD ENDINGS

Latin epithets (Specific, Variety, Form, etc.) are often adjectives in which case they should if possible use the same Latin gender as the Genus name, -a -us, or -um. Examples: Crassula ovata, Cereus peruvianus, Conophytum bilobum. However some plants have genus names derived from Greek, in which case gender is more complicated.

COMPOUNDING

Stringing together epithets in a name is popular and informative, however such names are rarely found in the official lists like the WCVP (World Checklist of Vascular Plants) supplied by Kew Gardens. An example of compounding is Lithops schwantesii subsp. schwantesii var. rugosa ‘Blue Moon’ which has two infraspecific epithets and also a cultivar name.

Often seen is a species that uses ‘subsp.’ being further divided by variety or form using ‘var.’ or ‘f.’ terms. Recent trends discourage compounding preferring subsp alone.

RANK

The above dissertation only covers binomial or trinomial naming which is just a part of the ranking of a plant. A more complete list is below. The principal ranks are more commonly used than the secondary ones.

In addition there are subdivisions of the principal and secondary ranks. From the ICN code: If a greater number of ranks of taxa is desired, the terms for these are made by adding the prefix “sub-” to the terms denoting the principal or secondary ranks.

In additiono there are other rarely used ranks which are too complex for this document, examples are superkingdom and infratribe.

Note that there are differences between the taxonomy of the plant kingdom and the animal kingdom.

More information at Wikipedia – Taxanomic Rank

Rank Hierarchy

Ranks applied to plants, in descending order.

Rank	Latin	Type	Suffix
kingdom	regnum	principal
subkingdom	subregnum
division	divisio	principal	-phyta
subdivision	subdivisio		-phytina
class	classis	principal	-opsida
subclass	subclassis		-idae
order	ordo	principal	-ales
suborder	subordo		-ineae
family	familia	principal	-aceae
subfamily	subfamilia		-oideae
tribe	tribus	secondary	-eae
subtribe	subtribus		-inae
genus	genus	principal
subgenus	subgenus
section	sectio	secondary
subsection	subsectio
series	series	secondary
subseries	subseries
species	species	principal
subspecies	subspecies
variety	varietas	secondary
subvariety	subvarietas
form	forma	secondary
subform	subforma

Example ranking: Crassula perfoliata var. falcata (J.C.Wendl.) Toelken

Clade

Many publications replace the ranking ‘Class’ with ‘Clade’ defined as a group of organisms composed of a common ancestor and all its direct descendants. A single plant can be a member of multiple clades and a clade can itself contain multiple clades, therefore clades are not considered hierarchical. The main use of clade is to indicate the evolutionary history of a plant.

The clades shown in Wikipedia for Crassula ovata (Jade) are:
   Tracheophytes – vascular plants
   Angiosperms – flowering plants
   Eudicots – having two seedling leaves

Strain

The term has no official ranking status in botany but is used to refer to a group of descendants produced by modification or mutation from a common ancestor that are similar in form. Plants within a strain show enough difference to each warrant a cultivar name. For example the group of Echinopsis known as “Schick Hybrids”. The strain name itself is not used in the binomial nomenclature.

COMMON NAMES

Common names are local names for plants and are usually in the local language. Although fun they cause confusion when trying to communicate between nationalities, even between regions within a nation. For example a web search for images of “Bluebell” will reveal at least a dozen different species.

CHECKLISTS

Checklist is a term used for a database maintained by an authority containing the accepted names of known plants.

The two main checklists for species are the World Checklist of Vascular Plants (WCVP) supplied by Kew Gardens and the World Flora Online (WFO). The WCVP checklist contains over 1.5 million names.

Checklists for cultivars are kept by various International Cultivar Registration Authorities, of which there are many, each being responsible for a small number of genera.

WCVP has an online interface at Plants of the World Online (POWO).
WFO is online at World Flora Online.
MOPDB by the author of this document has tools for searching the checklists at https://mopdb.shortsnet.com/taxonlookup

Non-cultivar plant names are registered at the International Plant Names Index (IPNI).

Cultivar names, as described above, are registered through the authority responsible for the particular genus. However finding lists of the registered cultivar names can be difficult. The overseeing body is the International Society for Horticultural Science (ISHS)

RENAMING

Driven by the results of molecular analysis (DNA), many species have been re-named recently. In the past, plants might have been given a unique name just because they didn’t look like any species known to the person naming them. DNA can find plants that are really the same species leading to one of them being renamed.

Name changes have been dubbed with the terms lumping and splitting, used by Charles Darwin back in 1857.
Lumping is when it is found that two plants are actually the same species, resulting in both being given the same (scientific) name.
Splitting is when it is found that two plants that had been given the same name are different, one of them is given a different name, possibly an already existing name.

LUMPING vs. SPLITTING: The choice depends on which is thought most important, similarities or differences.
A potential problem with lumping is the recovery of a previous name when future discoveries find that the differences really were important and they need to be split again. Once plants have the same name, nobody except the DNA analysts will know which are to be split unless there are visible differences. Whereas maintaining the extra information in the name, like the place of origin, can avoid such problems later. Lumping can also end up with a lay person finding it hard to understand how two obviously different looking plants have the same name.

Through time the number of accepted species has grown so much that lumping seems a good option. Someone may have given a plant an extra infra-epithet (especially var) because it looked different from the main species. Then it turns out that the visible differences can be reproduced when a plant from the main species is grown in the same conditions as the plant that was thought different.

The current trend seems to be lumping, much to the chagrin of many collectors and producers who need to print new labels. Also difficult for book authors whose heavily researched offerings become out of date.

Today we are much better positioned to correct some of the past mistakes, we have better communication and online databases accessible to all. Someone deciding if they have discovered a new plant can see a vast array of photos online to help with their decision.

It seems that we need to accept renaming, assuming that it will lead to improved accuracy, and with the hope that those making the changes get it right.

Flow Chart of Nomenclatural Bodies and Processes

The chart below is from the “International Code of Nomenclature for Cultivated Plants” ninth edition by ISHS. This chart demonstrates the relationships between the various international bodies that govern the international nomenclature of plants, resulting in the provision of a correct nomenclature.

Confused yet?

For more in-depth reading try “The Code Decoded” by Nicholas Turland.