With millions of species coexisting on planet Earth, there needs to be a way to name all of them. Taxonomy is the way different organisms are named, classified, and described. This system gives each species its unique name, making it easier to keep track of species. It was invented in the 18th century by Swedish botanist Carolus Linnaeus, which only had two layers of classification and is known as the Linnaean system. Modern taxonomy has eight layers.
Under the Linnaean system, organisms were grouped based on physical characteristics.
What are the eight taxonomic ranks?
The eight taxonomic ranks are:
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
An effective way to memorise anything is via a mnemonic device that makes a saying. The first letter of each word represents the desired word to learn.
You may have heard of this saying: Please Excuse My Dear Aunt Sally, which teaches the order of operations for maths.
A good way to memorise taxonomic order is:
Dear (Domain)
King (Kingdom)
Phillip (Phylum)
Came (Class)
Over (Order)
For (Family)
Good (Genus)
Soup (Species)
Domain in taxonomy
Domains are currently the newest addition to taxonomy after being added in the 1990s. This is known as the three-domain system because it split Bacteria and Archaea into their separate domains, known as prokaryotes. There are three different classifications under domains:
Bacteria.
Archaea (types of single-cell organisms that are similar to bacteria).
Eukaryota (every other living thing that is not bacteria or archaeon, this domain includes us, aka humans).
Domain names are always capitalised because otherwise, it could cause confusion. Bacteria, the domain, includes all bacteria; however, bacteria will typically refer to only one or a few species of bacteria.
Kingdoms in taxonomy
Kingdoms have one of the most controversial classification layers, with many changes over time. Some researchers ignore using kingdoms altogether because there is no agreement on kingdom classification.
The current breakdown of kingdoms are:
Archaea and Bacteria are occasionally combined to form a kingdom called Monera. Since Protista is somewhat of a “catch-all” kingdom, some biologists have recently called for splitting it up into Protozoa and Chromista.
Phylum in taxonomy
Phyla, the plural of phylum, are more specific than just using a kingdom for species classification and have been used since the 19th century. Phyla groups together species that are either evolutionarily related or have similar bodily traits.
The kingdom Animalia has thirty-five phyla.
Classes in taxonomy
Classes have been in use since Linneaus created them in the 18th century. As of right now, there are currently 108 different classes in the Animalia kingdom. These classes include Mammalia, consisting of mammals, and Reptilia, reptiles.
Botany, the study of plants, typically does not use classes. Since the first publication of the classification system in 1998, flowering plants have been classified up to order levels. Other sources preferred to treat the ranks as informal clades. Where ranks were assigned, they were reduced to a lower level.
Order in taxonomy
Classes break down into orders. For example, in Mammalia, there are orders such as Cetaceans, which refer to whales, dolphins, porpoises, and Primates.
Hint: Different sources will have different numbers of orders. For proper studying in class, use the numbers provided by your teacher.
Families in taxonomy
Orders have different families within them. In our previous order of Primates, there are nine families. These families are Lemuridae, large lemurs, and Hominidae, humans.
Genus in taxonomy
Genera, the plural form of genus, is the first part of the scientific name for an organism. The scientific name is always italicised, with only the genus being capitalised.
Homo sapiens is the scientific name for humans, and the genus is Homo. Other organisms with the genus Homo have existed, such as Homo erectus, but they are all extinct.
Species in taxonomy
Species are the second part of the scientific name for an organism and are the only taxonomic rank that is never capitalised. In Homo sapiens, sapiens is the species name.
If you need to abbreviate a scientific name, it is like this: H. sapiens.
Examples of taxonomy
We will cover an example, a human classification.
It is crucial to note that “Genus” and “Species” are written in italics. In an exam, if you are writing on paper, underline the words to highlight that you are writing in italics!
Is there another way Organisms can be Classified?
There is another way organisms, especially their species, can be classified. This method is known as the IUCN (the International Union for Conservation of Nature) Classification of Species. Each species has its population assessed and is assigned one of nine labels:
Not Evaluated
Data Deficient
Least Concerned
Near Threatened
Vulnerable
Endangered
Critically Endangered
Extinct in the Wild
Extinct
Hint: You have probably seen some of these labels on animal information signs at the zoo.
What do these Labels mean for Species?
These labels allow scientists to assess which species they need to prioritise with helping combat extinction. For example, species that are Endangered, Critically Endangered, and Extinct in the Wild will typically have breeding plans in captivity to help boost their numbers by releasing the offspring into the wild.
Taxonomy - Key takeaways
- Taxonomy is the way species are named, classified, and described.
- There are eight taxonomic ranks used to classify species. They are Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species.
- A way to memorise the taxonomic order is Dear King Phillip Came Over For Good Soup.
- The scientific name of an organism is the genus and species. The genus and species are italicised, but only the genus is capitalised.
- If two species have the same genus, they are closely related.
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