I. The Taxonomic Hierarchy
A. With
natural and phylogenetic systems of classification, members of
a group have more in common with one another than with members
of any other group. Instead of having to record and remember the
characteristics of every individual within a group, we only need
to know characters of group as a whole, and note exceptions. Natural
and phylogenetic systems of classification are predictive
and enable us to summarize knowledge because they are hierarchical.
B. The categories used for classification are defined by the International Code of Botanical Nomenclature (ICBN). An electronic version of the Vienna Code from 2006 is online here. This supercedes the previous code (St. Louis Code 2000) which is still available here.
"What's in a name? That which we call a rose
By any other name would smell as sweet"
Shakespeare, Romeo & Juliet (1594)
Let's look at the classification of a Carolina rose
| Rank | Example taxa |
| Division (or Phylum) | Magnoliophyta |
| Class | Magnoliopsida |
| Subclass | Rosideae |
| Order | Rosales |
| Family | Rosaceae |
| Genus | Rosa |
| Species | Rosa carolina |
| Subspecies | |
| Variety | |
| Form | |
| [Cultivar] |
- Binomial: composed of genus, specific epithet, and authority
- Taxonomic hierarchy as boxes within boxes.
C. Features of the Taxonomic Hierarchy
1. Names above the rank of GENUS (but not Genus itself) are based upon the name of an included genus. Each rank has a distinctive ending that is attached to the stem of the name of the genus, e.g. Rosaceae (-aceae ending on the genus Rosa).
2. The word TAXON is used to refer to a taxonomic category of any rank. The plural is TAXA.
3. The name of a genus is always underlined or italicized; the first letter is capitalized. The names of genera are treated as NOUNS. The plural of genus is GENERA.
4. The scientific name of a species is the combination of the name of the genus with the specific epithet = a BINOMIAL. Both are underlined or italicized. To be complete, the scientific name includes the authority or name of the person who described the species. The word species is both singular and plural ("specie" is a gold, silver or other coin).
5. It is always correct to write the specific epithet in all lower case [species named after people and after old generic names may be capitalized].
6. The specific ephitet is usually considered to be an adjective that modifies the genus (noun), and it agrees in gender with the genus. Exceptions include the names of many trees that were considered feminine (e.g. Quercus alba, not Q. albus).
7. When several species of one genus are given in sequence, the name of the genus can be abbreviated to its first letter. Always start a sentence by spelling out the full generic name, i.e. don't start with an abbreviation.
8. The authority can be abbreviated to save space, especially for authors who described a large number of species. The author's name is never italicized or underlined.
9. There may be joint authors, such as: Torrey & Gray, Fernald and Schubert, Britton and Rose; these may also be abbreviated: T. & G., Fern. & Schub., Britt. & Rose.
10. The names of subspecific ranks (subspecies, variety, form) consist of the name of the species followed by an abbreviation of the rank, the subspecific ephitet, and the authority for the subspecific name.
11. Alternative Family Names. Although both are allowed by the Code, we will use the -aceae ending names in PLB 304.
| Family Name | Alternate Family Name |
| Apiaceae | Umbelliferae |
| Arecaceae | Palmae |
| Asteraceae | Compositae |
| Brassicaceae | Cruciferae |
| Clusiaceae | Guttiferae |
| Hypericaceae | Guttiferae |
| Fabaceae | Leguminosae |
| Lamiaceae | Labiatae |
| Poaceae | Gramineae |
II. Principles of Botanical Nomenclature
A. The naming of plants is covered by the ICBN.
B. Features of Plant Nomenclature
C. Transfer between Ranks
1. When a genus, species, or subspecies is described at one rank and then transferred to another rank, the original author is placed in parentheses followed by the author who made the transfer, e.g. Linneaus named an alfalfa:
Medicago polymorpha var. orbicularis L. But, Allioni thought it was deserving of species status, so:
Medicago orbicularis (L.) Allioni In the transfer, the specific epithet "orbicularis" has priority and is retained because M. polymorpha var. orbicularis is the basionym or "name-bringing synonym". Note that the name of the original author (here L) is retained and placed in parentheses ahead of the new author.
2. The same situation occurs when a species is transferred from one genus to another, e.g. Linneaus named a plant Cheiranthus tristis L.
But Robert Brown thought it deserved status as a different genus, so he transferred it and now the name is Matthiola tristis (L.) R. Brown
3. When a subspecific taxon is named, another subspecific taxon of the same rank is automatically created that repeats the name of the species. This is called the AUTONYM.
For example, if the name Rosa carolina var. villosa (Best) Rehder is created, then another name, Rosa carolina var. carolina L. is automatically created (from the original R. carolina L.).
D. Names of Hybrid Taxa. In many plant groups, natural hybrids occur between species. For example, oaks (Quercus) are a group long known to form natural interspecific hybrids (PCA diagram). What do you do about naming these hybrids? Hybrids are indicated with the "X" sign and may be given in two forms, the first where the parental taxa are indicated, the second where the hybrid taxon is given a new name:
E. Names of cultivated plants. Through breeding, interspecific hybridization, and direct genetic manipulation, humans have produced an amazing array of different plants for use as food, ornament, etc. These plants are called cultivated varieties and their rank is CULTIVAR. The rules for how to designate them are as follows:
1. Treated as "fancy names" in a modern language. NEW cultivar names cannot be in Latin and may not be the same as the botanical or common name of a genus. Have a look here at some of the weird names people have come up with!
2. The fancy name is preceeded by the letters cv. or included in single quotation marks
3. The name is written in plain text, not underlined or italicized
4. The first letter of the name is CAPITALIZED
5. The rank of cultivar is NOT in the subspecific hierarchy, but may be used with any taxon from genus downward
Examples of correct cultivar names of apple, Malus baccata Borkh.:
- M. baccata cv. Columnaris
- M. baccata 'Jackii'
- Malus 'Barbara Ann'
F. Priority of Names
1. Nomenclature is based upon priority of publication, i.e. the earliest legitimate name is the correct name (but note exceptions below).
2. Each taxonomic group can have only one correct name, which is the earliest that is in accordance with the rules, except in specified cases.
3. Priority begins with the publication of Linnaeus’ Species Plantarum on May 1, 1753 and applies to the rank of family and below.
4. The correct name of a species is the combination of the earliest published valid generic name with the earliest published valid specific epithet.
5. The same taxon has often been described and named more than once. The later names are called SYNONYMS and are illegitimate. But you may be wondering, "who decides that the later-named taxon is the same as the previously-named one?" This falls under taxonomic discretion of the person doing the work - hopefully an expert on that group who often writes a monograph (a revision of a genus, family, etc. over the plant's entire range worldwide).
6. The same name has often been used for more than one taxon, called HOMONYMS:
7. To avoid the disadvantages of a strict application of priority, the International Botanical Congresses have authorized the CONSERVATION of widely used names, even though they are NOT the oldest names. These nomina conservanda (conserved names) may be at the family, genus, and species ranks.
III. The Type Method
A. The names of taxa are based on nomenclatural types, which permanently fixes a name to an actual PHYSICAL SPECIMEN. Note: the type does NOT have to be typical of the species.
B. Ideally, the type of a taxon is the one herbarium specimen upon which the author of a taxon based the name. This is the HOLOTYPE.
C. An ISOTYPE is a duplicate specimen of the holotype.
D. It did not used to be a requirement to designate a type, and today it is often necessary to select one of the original specimens as the LECTOTYPE.
E. Many herbaria are in the process of digitizing their collections. This is especially important for types. New York Botanical Garden has been cataloging and imaging ca. 92,000 of its vascular plant type specimens. Visit the NYBG here.
IV. Valid Publication, i.e. requirements for describing a new plant
A. Have a Latin diagnosis or description
B. Give a clear indication of rank
C. Designate a type and its location
D. Publish in a scientific journal
E. Accept the name yourself (not just an incidental mention)
F. Follow the rules of nomenclature according to the most recent Code.
