A Quick Course in Plant Taxonomy

First, a disclaimer. I am no expert in plant taxonomy. I will explain this as best I can.

If you want to go to the source, start with the International Association of Plant Taxonomy. Their rules are enshrined in the International Code of Botanical Nomenclature (ICBN). The ICBN is quite long, detailed, and generally dry and boring with moments of real excitement (if you’re a plant nerd). Thankfully, it is all on line ( As the .sk indicates, their main office is in Bratislava, Slovakia. The information in this section is primarily drawn from the ICBN.

Here are some of the main points.


Classification is in the familiar hierarchy.








Various groupings and divisions may be nested within this general structure, such as Subkingdom, Superdivision, Subclass, Tribe, Subspecies, etc.


Priority and Name Changes
The earliest valid identification wins. Priority is determined by the first published document that validly identifies the species (and much ink is dedicated to what a validly published document is). If you have been using a particular name, and then an earlier published ID for the same species is verified, you change to the earlier version.

If someone demonstrates that a species name was misapplied and belongs in another genus, family, etc., the name will change accordingly. If a valid species needs to be switched to another genus, you keep the species name if possible. (eg - Myrica californica --> Morella californica).

These changes will happen to you over and over again. Get used to it.


Family Names
Family names
must end in -aceae, such as Asteraceae and Betulaceae. The family name must be based on the name of a genus within it. For example, in the case of Asteraceae, the family name is based on the genus Aster.

A number of old, venerable family names, such as Leguminosae were changed to conform to the new rules. For example, the name "Leguminosae" fails under the new system because there is no genus Leguminus and also because Leguminosae ends in '-sae' rather than '-ceae'. It was changed to Fabaceae.

Turns out, however, there is also a rule that historical names of major standing are still considered valid. It’s probably best if you use the new names, but if you want, you can still legitimately use Compositae, Graminae, Leguminosae, Cruciferae, Labiatae, Palmae and Umbelliferae. They are “treated as validly published”, whatever that means.


Genus Names
Genus names must be nouns, and are conjugated in the male or feminine form in latin.

Here are a few of their guidelines:

• Use Latin terminations insofar as possible.

• Avoid names not readily adaptable to the Latin language.

Do not make names which are very long or difficult to pronounce in Latin. (Schoenoplectus? Who let that one through?)

Do not make names by combining words from different languages.

Indicate, if possible, by the formation or ending of the name the affinities or analogies of the genus.

Avoid adjectives used as nouns.

Do not dedicate genera to persons quite unconnected with botany or at least with natural science.

Give a feminine form to all personal generic names, whether they commemorate a man or a woman.


Species names
“The name of a species is a binary combination consisting of the name of the genus followed by a single specific epithet in the form of an adjective, a noun in the genitive, or a word in apposition, or several words.... If an epithet consists of two or more words, these are to be united or hyphenated.”

Genus and species are typically shown in italics. Some prefer to show them underlined.


Subspecies and Varieties
I have not located rules within the ICBN to determine whether something below the level of species is a subspecies or a variety, although it has many rules on how to construct the name.

The way I learned it, a subspecies is regarded as a major subgroup of the species, where there are many individuals found within a region or a habitat type. A variety is particular form of a species that is found in one individual or in a limited population. A cultivar is simply a cultivated variety. Normally, it is a selection from one individual.

Example - Bigleaf Maple




Magnoliophyta - Flowering Plants










Acer macrophyllum


California Native
Plant Guide


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