Fun with Taxonomy: Trinomial Nomenclature

Science Ahead Warning!: Much like Dr. Sheldon Cooper and his friends, the staff of MOSI Outside are dedicated geeks. We love entomology and etymology, zoology and botany and the curious naming conventions of all living things. Thus, in our geekery, we wish to give the gift of a taxonomic explanation series that we shall call: Fun with Taxonomy. 

We're awfully fun at parties. 

In an attempt to protect all brains from accidental science content, we will helpfully label all posts in this series with a tree of life image. When you see this tree, mentally prepare yourself for science content, terms with which you may not be familiar, and possibly a few history lessons. Get yourself a cup of tea and dive into some science. Now, let's have some Fun with Taxonomy!

Trinomial Nomenclature

Most of the time, when you see something listed by its scientific name, you will see a pairing of words that tell you the genus and species of the organism. That system of distinct and unique pairings is called binomial nomenclature, and it is what science uses to track an organism that may have different common names in different places. You can learn more about the basics of the classification of all life here: Fun with Taxonomy: How Do We File Life?

Trinomens and Polytypic Species 

Distribution map of Limenitis arthemis.
The red shows the range of L. a. arthemis;
the orange L. a. astyanax;
the green L. a. arizonensis;
and the yellow shows where the
ranges of L. a arthemis and L. a. astyanax overlap.

In zoology, Trinomens or Trinomial names are used to designate one level below species: subspecies. Subspecies are considered to be permanent and geographically isolated from other members of their species and often have special adaptations or different coloration than other members of their own species.

A species with more than one recognized subspecies is considered Polytypic. One example from the world of butterflies would be the species arthemis. This species is polytypic and has multiple recognized sub-species or variations.

• American White Admiral (Limenitis arthemis arthemis) has distintive white banding on its wings and is sometimes also classified by the scientific name of (Limenitis camilla)
• Western American White Admiral (Limenitis arthemis rubrofasciata) has no blue spots on its inferior wings.
• Red-spotted Purple (Limenitis arthemis astyanax) lacks the distinctive white bands that mark the other members of the species but is limited in range to the American southeast.
• Arizona Red Spotted Purple (Limenitis arthemis arizonensis) lacks the distinctive white bands that mark the other members of the species but is limited in range to the American southwest.

Each subspecies is given a third subspecific name to differentiate it from other portion of the overall species. Much like with specific epithets, these names usually describe a location where the subspecies is found, an observable and distinctive trait of the subspecies or sometimes the name of a person who discovered or was honored by the naming of the subspecies.

Here in Tampa, Florida, we will only see the Red-spotted Purple butterfly. Each species has a geographically distinct range and in this case, the various subspecies can have an incredibly varied appearance.

However, in the Land of Botany...

Trinomens are all well and good for the well ordered world of zoology, but in botany there is more than one rank recognized below the level of species. In fact, there really isn't a good way to number the possibilities for ranks below that level. Subspecies, variety and forma can all be used as classification below the rank of species. However, you can also have a subvariety, a subforma and even the sort of insane classification of supersubspecies.

How plants are classified really comes down to which taxonomist is doing the naming. Some taxonomists prefer subspecies, and some prefer to use variety to denote differences within a species and there is no good agreement on when one or the other should be used. Yeah, botanical taxonomy is sort of the Wild West of the taxonomic world. Let's talk about that another day.