Nomenclature, Names, and Taxonomy
Internal links; Nomenclature, Scientific names, Pronunciation, Taxonomy, Towards and International Code; PreLinnaeus; Other Codes; First International Code; Limitations; The Code; Principles; Key Provisions, Form of names; Family names; Names of species; Publishing names; Writing names; Authorities; Changing names; Common names, Official names, Botanical Hierarchy, New names


Nomenclature refers to the naming of things.  Botanical nomenclature is (surprise) about naming plants.  Bear in mind that plant names refer to abstract entities - the collection of all plants (past, present, and future) that belong to the same group. As you will recall, taxonomy is about grouping.  Botanical nomenclature is about applying names to taxonomic groups. 

Scientific names of plants reflect the taxonomic group to which the plant belongs. One must first decide on the groups to be recognized; only then does one start to be concerned about assigning an appropriate name to the plant. Common names, at least those that are genuinely common names, usually reflect some conspicuous or valuable characteristic of the plant, not its taxonomic group.  The following comments are about scientific names.

Scientific names are never misleading.  No matter where you are, every plants has only one correct name. so long as its taxonomic treatment is not in dispute.   This last is a major reservation, but we can ignore it for now. The universality of scientific names means that even English speaking people can find out what species grow in China or Saudi Arabia by reading a technical flora of these countries.  Not only are the names the same, they are always written in the Latin alphabet (which is the same alphabet as these notes).  

Pronunciation. There is as little point about worrying over the 'correct' pronunciation of scientific names as there is in worrying over which is the correct pronunciation of English words. It may be difficult to recognize a scientific name if it is spoken by someone from another part of the world BUT one can always recognize it when it is written out.  In this, scientific names are no different from other words.  Think how hard it can be to understand different versions of English.  Nevertheless, it is advantageous to  use the same pronunciation as the other people you work with. Just be prepared to modify your pronunciation if you move to another part of the world.  

Taxonomy refers to forming groups.  Plants that belong to the same group have the same name.  The taxonomic decisions concerning how a group is to be treated (what goes in the group, what rank it should be recognized as ) MUST be made before it can be assigned a name.  It does not matter how you decide what its affinities are (unless, of course, you want others to support and use your treatment), but you must make these decisions before you can decide on an appropriate name for the group.  So remember, taxonomy first

If people are going to communicate around the world, there needs to be an internationally accepted system of nomenclature.  Creating such a system was not, and is not, an easy task.  It was not until 1930 that agreement was reached on an International Code had become standard around 1753. There were, however, many areas where there was widespread agreement in practice, with some of the practices dating back to before Linnaeus. For reasons that you will learn later, Linnaeus is taken as the starting point for botanical nomenlcature. Let's consider for a moment some of the areas of agreement that existed before there wasformal agreement on an International Code of Botanical Nomenclature.

Towards an International Code

Pre-Linnaean Practices

1) Names were formed like Latin words. The reason is quite straightforward; Latin was the common language among all European peoples - and plant taxonomy as we know it has its origins in Europe.   

2) Once a name had been attached to a plant group, it should not be given another name.

3) When commenting on how a name was to be interpreted, one should list the names of others that had used it.   

4) It helps to mention some specimens that one has seen.  

The first attempt at developing an international agreement was made in Paris in 1867.  At this meeting, it was decided that a) the first edition of Linnaeus' Species Plantarum, which was published in 1752, would serve as the starting point of botanical nomenclature and b) if two names had been given to the same plant group, the older name would be the correct name. In addition, various rules were laid down as to what was required to valid publication - a phrase that means "published in such a manner that the name counts". For instance, publication of new names in horticultural catalogs used to be acceptable, but it is not any longer.   

Other Codes

In 1892, a group of US botanists held a meeting in Rochester at which they presented some additions and modifications that they considered more objective (a great phrase in science). Among the changes that they proposed were that a) when publishing a new name one should cite at least one herbarium specimen representing the plant group concerned and b) that, when a species was moved from one genus to another it should, if possible, keeps its specific epithet (it is not possible if that epithet has already been used for another species in the new genus). Some of the new rules conflicted with those proposed in Paris, and the modified version being used at Kew, a major taxonomic center in England. 

Agreement, at last

In 1930, taxonomists finally agreed on a single International Code of Botanical Nomenclature. This Code is revised every 6 years, but the goals of all the revisions are always to achieve stability in scientific nomenclature and or to clarify problems.  The revisions are published in Taxon, the journal of the International Society of Plant Taxonomists, then voted on at a meeting that is held immediately prior to an International Botanical Congress. The last edition of the Code was published in 2000. There is a copy in the herbarium.

Limitations of the Code

Before considering what the Code says, it is important to know what it does, and does not, attempt to do.  

It DOES state what to do when you wish to assign a new name to a plant group, how the names of plant groups are to be informed, how to inform people about new names, and how to choose between two (or more) names that have been given to the same plant group.

It DOES NOT provide any information on how to decide whether a group of plants should be given a scientific name or what rank a group should have. These activities are taxonomic, not nomenclatural.  

Remember: Taxonomy comes before nomenclature. 

The International Code of Botanical Nomenclature

Becoming an expert on botanical nomenclature requires several years of study beyond graduate school, plus access to old, and often rare, literature.  A knowledge of Latin is also essential because many earlier works are in Latin.  What follows is a distillation of some of the keys points of the Code, points that you should endeavor to understand.  Some are presented in rather simplified form; be sure to consult the Code itself, plus a nomenclatural expert, before starting a serious argument or proposing a new name.

Principles of Botanical Nomenclature

There are six principles that guide decisions concerning the Code. 

Uniqueness Principle (Principle IV). The uniqueness principle states that there is only one correct name for a particular taxonomic group within a given taxonomic treatment. It is the central principle upon which all the remainder of the code is based. If people disagree on the taxonomic treatment, they will consider different names to be correct but, within any treatment, each taxonomic group has only one correct name.

Type Principle (Principle II).  The type principle states, "The application of names of taxonomic groups is determined by means of nomenclatural types".  For vascular plants such as grasses, a nomenclatural type is a herbarium specimen that has been deposited in a herbarium. A nomenclatural type anchors the meaning of a name. If there is an argument as to what kind of plant the author of a name meant by a particular name, one examines the type specimen.  No matter what taxonomic treatment is followed, the name must be used in a sense that includes its type specimen.  If, as occasionally happens, the author of a new name provides a description that does not match the type specimen, it is the type specimen, not the description, that determines what kind of plant is called by the name in question.   

Adherence to the type principle did not become mandatory until 1958. Prior to that time, when taxonomists published a new name they frequently simply listed several different specimens that exemplified what they meant by the name, without identifying any particular specimen as the ‘top dog’ among the examples.  All the designated specimens, including their duplicates, are referred to as syntypes: nomenclatural types of a single name, all of which were equally important. This became a problem if later taxonomists decided that there are two or more taxa among the specimens listed. When this happens, it became necessary to determine which of the specimens listed belongs with the original name.

To prevent such situations arising, the rules for designating a type specimen were made more explicit. Since 1990 it has been necessary to identify the exact specimen that is to be the nomenclatural type of the taxon, and the herbarium in which the specimen is located.  Between 1958 and 1990 it was enough to specify who collected the specimen, where it was collected, the date on which it was collected, and the collection number it was given, if any.  The problem was that, if the collector made several duplicate specimens, each of the duplicates is a syntype.  In most instances this is not a problem, but occasionally the supposed duplicates turn out to belong to different species. Requiring that an author state exactly which of the specimens is to be regarded as the nomenclatural type helps prevent even this kind of problem.  If possible, the accession number of the type should be specified as well as the name of the herbarium in which it is located, but many older herbaria do not give their specimens accession numbers.

 There are several different kinds of type specimen, but the most important are holotypes, lectotypes, neotypes, and epitypes. The next most important are isotypes, syntypes, and paratypes.  The first four kinds of type refer to specimens that are, unequivocally, the nomenclatural type of a name.  A holotype is a specimen that has been designated the nomenclatural type of a name by the person creating the name. If the person who originally published a particular name did not designate a holotype, a later taxonomist may select a specimen to serve as the nomenclatural type. This specimen then becomes what is called the lectotype of the name. If the holotype or lectotype is destroyed or lost, a new type specimen can be selected. Such replacement types are called neotypes. 

An epitype is a specimen selected to be the nomenclatural type of name for which there is a holotype, lectotype, or neotype available. Why would it be necessary to select another specimen as a nomenclatural type?  Sometimes the holotype, lectotype, or neotype simply does not show the features that are needed to determine, unequivocally, to which of two taxa it belongs.  In such a case, it cannot be used to fix the meaning of a name. In such situations, another specimen can be selected as the ‘anchoring’ specimen; it is this specimen that is the epitype.

Priority Principle (Principle III).  This principle states, in essence, that if a taxonomic group has been given two or more names, the correct name is the first name that meets the Code’s standards for publication. Basically, this means that the priority of a name dates from the time that it was first published and made known to other botanists. Writing the name in a letter (or Email) to a colleague does not count, nor do notes made on herbarium sheets. 

Taxonomic groups may end up with two or more names for several reasons.  The most common reason is taxonomic disagreement, about which the Code says nothing.   Sometimes, the person publishing a later name is simply unaware that the group has already been named.  In other cases, two (or more) names were given to different looking specimens of what was later treated as a single group. Whatever the reason, the priority principle states that only the first name validly and legitimately published for a particular taxonomic group is correct.

In determining priority, the date that matters is the date on which the material was actually mailed to other institutions; this is not always the same as the year on the cover of a book or journal.  

Retroactivity Principle (Principle VI).  This principle states, “The Rules of nomenclature are retroactive unless expressly limited”.  The Retroactivity Principle means that anyone proposing a change in the Code needs to consider the effect that the proposed change will have on names published in a wide range of literature and over a considerable period of time. This is an intimidating requirement. It is why all proposed changes to the Code undergo committee scrutiny before being voted on. If the committee has a problem with a proposed change, one of its members will get in touch with the person proposing the change. The committee member may point out unforeseen consequences of the proposed change. Alternatively, he or she may suggest examples that will make a stronger case for the change, or suggest modifications that will avoid some undesirable consequences.

All proposals to change the Code  are published in Taxon, but they remain proposals until they are voted on at the next International Botanical Congress.

PRINCIPLES 1 and V. The other two principles are straightforward. Principle I states that botanical nomenclature is independent of zoological and bacteriological nomenclature.  If an organism is considered to be a plant, then it must be named in accordance with the Botanical Code. If it is considered a bacterium, it must be named according to the Bacteriological Code.  Principle V states that scientific names are to treated as if they were Latin, regardless of their derivation. 

1.  Any changes in the Code should be designed to increase the stability of plant nomenclature.  No one likes name changes, not even the taxonomists that propose them.

2.  Every plant belongs to a species, every species to a genus, every genus to a family, every family to an order, every order to a class, every class to a division (also called a phylum nowadays - a concession to the greater number of zoologists in the world).  This is the taxonomic hierarchy.  Note that the Code assumes the existence of species.  It does NOT state what constitutes a species, let alone discuss whether species are real.  The Code also requires that plant diversity be summarized in a hierarchical structure.  Again, it is not a question of whether such a structure really exists. The fact that the Code assumes the existence of species and a hierarchical structure does not mean that that the assumptions are correct, merely that, in naming plants (and the zoological code is similar in this regard), one must act as if species are real and nature is hierarchical. Many people object to this, but no one has provided a persuasive argument for dropping the system. 

PUBLISHING SCIENTIFIC NAMES.  Before a name, even a name that has a Latin form, can be accepted as a scientific name, it must satisfy several criteria.  Some of these have to do with its form, others with how its existence and meaning are made known to others. 

Form. Principle V states that a scientific name must be treated as if it were Latin, but the Articles 16-28 of the Code also specify what form the name must take. I have summarized them in the table below.  

Rank Ending Examples
Division (Phylum) -phyta Pinophyta, Magnoliophyta
Class -opsida Pinopsida, Liliopsida, Magnoliopsida
Order -ales Pinales, Liliales, Magnoliales
Family -aceae Pinaceae, Liliaceae, Magnoliaceae
Tribe -eae Pineae, Lilieae, Magnolieae
Genus A noun Pinus, Lilium, Magnolia
Species Depends Pinus flexilis,Lilium grandiflorum, Magnolia grandiflora
Variety Depends Pinus flexilis var. humilus
Form Depends  

Family names must be formed by combining a generic name with the suffix –aceae, but there are eight exceptions to this rule.  Each of the eight exceptional names was almost universally used, and used in the same sense, throughout the world when the first edition of the Code was prepared and so, in accordance with the overriding goal of achieving nomenclatural stability, it was agreed that they would continue to be used. The eight names are Gramineae (Grass Family, alternative Poaceae) Palmae (Palm Family, alternatively Arecaceae), Cruciferae (Mustard Family, alternatively Brassicaceae), Leguminosae (Pea family, alternatively Fabaceae), Guttiferae (St. John’s Wort Family, alternatively Clusiaceae), Umbelliferae (Carrot Family, alternatively Apiaceae), Labiatae (Mint Family, alternatively Lamiaceae), and Compositae (Daisy Family, alternatively Asteraceae).

The name of a species is ALWAYS a binomial.   'Grandiflora' is not the name of a species.  It has to be combined with a generic name to form the name of a species, as in Magnolia grandiflora.   The word 'grandiflora' is what we call the specific epithet.  It states which species of Magnolia is under discussion.  Specific epithets are often adjectives that describe some attribute of the plant (it helps to learn a little Latin - 'grandiflora' means large flowered), but may refer to the habitat of a species (pratensis -of fields, lacustris - of lakes, saxicola - of rocky places), the place where the species occurs (chinensis, europaea, canadensis), or a person that is somehow connected to the species (the connection may be remote) - wrightii (referring a single, male person named Wright), wrightiae (referring to a single female person named Wright), wrightorum (refering to 2 or more people, one of whom - and possibly only 1 out of a 100 - was male) or wrightarum (referring to 2 or more people with not even one male among them - the Romans were sexist).  

Technically speaking, subspecies is a higher rank than variety.  A subspecies may include several varieties.  In practice, most taxonomists nowadays use one rank or the other, but not both.  Europeans tend to use subspecies and expect subspecies to occupy somewhat different areas whereas Americans use variety to denote plants that are different from the plants first put in the species.  In practice, the two ranks are used almost interchangeably. 

There are several optional ranks that are not listed above.  For more information, consult the Code. 

Writing Scientific Names 

In North America it is customary to write names at the rank of genus and below in italics or some other font that sets them apart from the rest of the text.  The most recent edition of the Code recommends that all scientific names, no matter what their rank, be in a different font from the rest of the text. Either practice makes it easy to scan for taxonomic information.

The names of all ranks from subgenus up MUST be capitalized.  In most instances, the specific epithet - and epithets for lower rankings, must NOT be capitalized.   There are some exceptions to this rule, cases where it is permissible, but not required, to capitalize the specific or varietal epithet, but you need to be careful.   Personally I recommend always using lower case for epithets (names distinguishing species and lower ranks).  That way one is never wrong. 


You will notice that scientific names are often followed by a word or a capital letter and a period, or one or more unintelligible (to the uninitiated) sets of letters.  To join the initiated, read on.

The letters and/or words that follow a scientific name (sometimes they may be within a name - more on that later) are a shorthand reference to the name of the person or person that first gave a name to the entity involved and, in some instances, to the person of persons who first treated it at the rank being used.  This is probably easier to understand through some examples.

Consider Oryzopsis exigua Thurber

Note that only the first two words are italicized. This means you are looking at the name of a species.  'Thurber' is the last name of the person who first gave a name to this species - and the name he gave to it is the one shown.  

Consider "Oryzopsis asperifolia Michx." 

Again, you are looking at the name of a species in the genus Oryzopsis. This species was first named by a fellow whose name is abbreviated to Michx.  The period tells you that his name has been abbreviated.  His full name was Michaux.

To whom do you think "L." refers to in "Triticum aestivum L."?

"Dichanthelium lanuginosum (Elliott) Gould"

The name is Dichanthelium lanuginosum. As you immediately recognize (because the name is a binomial), the entity being named is being treated as a species. The first person to give a name to this species was a chap whose last name was Elliott, but he named it Panicum lanuginsoum. An inner circle of initiates could tell you that Elliott refers to Walter Elliott, who lived from 1803 to 1887, in eastern North America (There is a book called Authors of Plant Names that provides such insight). 

"Gould" stands for Frank W. Gould came along later and decided that, although Elliott was right in describing the species, he should have put it in a different genus, the genus Dichanthelium. Elliott's name is in parentheses to show that he was the first person to say "Aha, these plants are different"' Gould's name is outside the parentheses because he said, yes, Elliott was right - these plants are different - but they should be included in the genus Dichanthelium, not Panicum

Consider "Distichlis spicata (L.) Greene

Linnaeus [L. stands for Linnaeus] first described the entity, but as Uniola spicata, not Distichlis spicata.  Greene was the first person to say no, these plants should be in Distichlis and then publish the combination "Distichlis spicata".  Linnaeus gets credit for being the first person to describe the entity, Green for being the person to give it the name shown.  

Most journals, and consequently many professors, ask that you cite the authorities for a name when it is first used. It is a rather meaningless exercise. It is meant to say "I am using this name in the sense that it was used by Greene (in the last example)", but really you are probably using it in the sense that it is used in some flora - or based on what your boss told you.  The 1999 Congress encouraged editors to be more rational about when it was useful to cite authorities and when not, but I suspect that most journals will continue to require them for some time to come.   

If you have to publish a new name or combination, the Code requires that you follow certain rules (which it calls articles).  The key requirements are that:
1.  The new name or combination be published in a normal botanical outlet (not the Herald Journal or Statesman), copies of which are sent to at least two botanical institutions.
2.   If the name is for a new taxon, the distinguishing characteristics of the taxon, and preferably a full description, must be given in Latin and a holotype specified.
3.   If the name is simply a new combination, perhaps reflecting the transfer of a species from one genus to another or its demotion to a subspecies, there must be a clear and complete reference to the place where the original name was first published. 

1. Discovery of an older name for the taxon that has been overlooked. In the last decade, it has become possible to conserve the name actually being used if one can show that the earlier name has never become established. This is a nomenclatural, not taxonomic reason, for changing a name.
2. Discovery that the name being used for a particular taxon had been applied earlier to some other taxon. This is a nomenclatural, not taxonomic reason, for changing the name.
3. A decision that a species belongs in a different genus, or that a taxon needs to be split, or that the rank of the taxon needs to be changed. These are all taxonomic decisions. 

Most name changes reflect taxonomic decisions, but people that do not agree with the decision may continue to use the existing name.  This is what non-taxonomists find frustrating, if not infuriating.  Such people often become even more frustrated when told that there is no set of criteria nor any governing board that determines at what rank a taxon should be recognized at, or what its boundaries should be. There are stronger and weaker arguments, but there is not even complete agreement on which are strong arguments and which are weak.  Taxonomy is not a field for those that require certainty in their life. 

Other Names

Plants are often known by many different names.  The names Convolvulus arvensis; Bindweed, Field bindweed, Common bindweed, Small bindweed,
Morning glory, and Liseron des champs all refer to the same species. The scientific name is Convolvulus arvensis. The other names are what are called common names or vernacular names. I prefer the phrase 'vernacular name' because many so-called common names are simply names constructed to satisfy the demand for a name in a familiar language - they are not names in common use.  

Although many people like 'common names', there are many problems associated with them. For instance, Indian ricegrass (Achnatherum hymenoides) is not a close relative of either rice or wild rice (two very different species), but it was used for food by Native Americans and looks something like short grain rice.  I regard it as a genuine common name - among English speaking people. But the species was an important component of the diet of the Native Americans in Utah and the west. I rather doubt that it is called Indian Ricegrass in any Native American language.

Sometimes, the common name is the same, or partly the same as the scientific name. Many of you probably have no problem understanding Penstemon and Delphinium, but both of these are scientific names.  If you grew up in England or Australia, you would also be familiar with Capsicum as a common name, but in North America the commonly encountered species of Capsicum are called bell peppers or chili peppers. Despite their American names, species of bell peppers and chili peppers are more closely related to potatoes, eggplant, and nightshades than the kind of pepper that we use in pepper grinders.   

Problems arise when vernacular names have been created based on scientific names, but the meaning of the scientific name changes. For instance, all species in the genus Agropyron were given common names that incorporated the word 'wheatgrass'.  The trouble is that most of these species have since been kicked out of Agropyron.   It is not a huge problem, but it does point up how artificial so many 'common names' are.

Another problem with common names is that they  may apply to more than one species.  Corn used to the name for the grain most used for flour. In England, corn meant wheat; in Scotland, it meant rye or barley; in these two countries what Americans call corn was known as maize.  With the increasing dominance of American English, corn is now generally interpreted as meaning Zea mays - otherwise known as maize.  Similarly 'Bluebell' forms part, or all, of the name of many different plants. I learned of it as referring to monocots that are sold here as Wood hyacinths.  In Scotland, it applies to what I would call a Harebell. but the northern Utah flora refers to as Arctic bellflower. This same work gives Bluebell as the common name for Mertensia, a third genus and a third family. The USDA PLANTS database lists 18 different species as having Bluebell as part of their common name.  

Even in one's own language, common names can be rather obscure.  Do you know what plant is meant by Jack-in-the-Pulpit? Actually, that one is not bad. But how about "Welcome home husband no matter how drunk you may be"?  Yes, I have seen it listed as a common name.  Clearly the people that use it are not bothered by long names. And no, I have never met anyone that uses it.

Common names have local value; scientific names have universal value. in this class, we focus on scientific names. 

Official Names  

In some countries, one or more government agencies creates plant names in the country's native or official language which they require their employees and contract employees to use.  Some of these names are what I would refer to as the truly common names, but many are just extensions of a true common name to other species, often by translating the specific epithet.  Official names can be useful in talking to non-botanists, but the result is often a parallel system of nomenclature.  The U.S.A. is one such country.  Indian ricegrass appears to be a genuine common name, that is, one that ordinary people coined and used, for the species that used to be known as Oryzopsis hymenoides.  Unfortunately, the USDA decided that all species of the genus Oryzopsis should be called ricegrasses so the official name of O. kingii became King Ricegrass and O. asperifolia became Roughleaved ricegrass although neither of these species has ever been used as a source food for humans.  The problem with this approach to creating official names (which are generally called common names) is that taxonomic study shows that neither Oryzopsis hymenoides nor O. kingii belongs in Oryzopsis.  Oryzopsis hymenoides is now placed in either Achnatherum or Stipa (there is taxonomic disagreement) while O. kingii is placed in the genus Ptilagrostis.  Should the official name of P. kingii be changed from King Ricegrass? If so, to what?

There are other problems with having official names. For instance, several years ago, the old Soil Conservation Service sent out an updated list of approved common names for Utah's plants.  Among other idiocies, it was proposed that people should stop referring to penstemons (unless using a scientific name) and start referring to the species involved as beardtongues even thought the vast majority of the official names (which were called common names) were basically a translation of the binomial.  In my opinion, it makes more sense to teach people to refer to Eatons Penstemon rather than Eatons Beardtongue.  At least that way they learn half the scientific name.    

Choose your name:

Convolvulus arvensis
Field bindweed, Common bindweed, Small bindweed,
Morning glory, and Liseron des champs

All these names apply to the species shown below. Convolvulus arvense1.jpg (2109556 bytes)

Convolvulus arvense2.jpg (4048491 bytes)

Convolvulus arvense3.jpg (2970704 bytes)