What is taxonomy? Taxonomy is the branch of science that classifies organisms into different groups or types based on their characteristics, and more recently, their DNA. All organisms on earth are sorted into classifications, and then given a name based on that classification. I like to think of taxonomy as the library of living things.

This library of living things makes life easier for biologists. There are A LOT of organisms on Earth (approximately 9 million different species) and without a way to classify them we would be utterly lost. Even with our modern day taxonomy, there is still plenty of room for confusion and disagreement. Scientific names might seem like a foreign language at first, but this language is universal for all scientists and once you understand it, you can communicate about biology a lot better!

Out of the approximately 9 million species on Earth, about 400,000 of them are plant species.

But, what is a “species”? And what even makes something a “plant”, anyway? We might understand these words at some level but they take on an important meaning when it comes to taxonomy.

Plant Domain and Kingdom

The graphic above shows the tiers of classification in taxonomy, starting with Domain. There are 3 domains of all life: Archaea, Bacteria, and Eukarya. All plants and animals are in Eukarya because their cell has a nucleus. You may have heard the phrases plant kingdom and animal kingdom. The “Plant” classification is at the kingdom level. The scientific word for the plant kingdom is “plantae”.

Plant Phyla

After kingdom, the classifications of plants becomes a lot more specific. There are 14 different phyla in the plant kingdom. Another word commonly used for “phyla” is division. The biggest phyla (contains the most species) in the plant kingdom is the Anthophyta (previously called Magnoliophyta), which is the phyla of all flowering plants. Flowering plants make up at least 75% of all plant species. Flowering plants can also be referred to as angiosperms.

Plant Classes and Orders

Next is class, and below that is order. Class names for plants end in “-opsida”. The two main plant classes are Magnoliopsida (also called eudicots – meaning two seed leaves) and Liliopsida (also called monocots – meaning one seed leaf).

Plant order names end in “-ales”. Not all plant families are in orders but there are several plant orders that contain multiple plant families. Here is a chart from the Botanical Journal of the Linnean Society, Volume 141, Issue 4, April 2003, Pages 399–436 that shows plant order classification:

Plant Families

The plant family is typically the highest classification that we refer to when discussing individual plants. It is rare to discuss the class, order, or phyla of plants unless you are discussing the plants taxonomy at a deeper level. However, we sometimes will bring up a plant’s family when discussing an individual plant to give more context about its useful or visual characteristics.

There are over 600 plant families but each family has its own classifying traits. There is a great working list of all plants in the world and their families over at The Plant List.

I say “working” because the library of plant taxonomy is constantly being updated and added to. This is part of what makes taxonomy so interesting! We are finding better ways to classify things all the time, and we are finding new plants to classify every year as well.

Plant Genera and Species

The genus and species is how we typically refer to an individual plant. In fact, the genus and species is exactly what makes up a plant’s scientific name! This is why scientific names are two words. The proper format for writing scientific names is to capitalize the genus (the first part of the name) only, and to italicize both words.

A genus can contain just one species or it can contain one hundred species. What determines if multiple species are in the same genus is how structurally related they are.

Finally, we have species: the most granular level of classification on the taxonomic pyramid. A species is determined by common characteristics as well as the ability to reproduce. If 2 individuals in the same genus can reproduce, they are considered to be the same species.

Subspecies, Varieties, and Cultivars

Beyond the taxonomic pyramid, we have even more ways to classify plants. Subspecies, varieties, and cultivars are some of these additional classification methods. Since these go a bit beyond the basics, I will save exploring them for a later time, but let me know if you would like me to write about these methods more in a future blog post.

Also, check out my blog on the taxonomic terminology for flowers to learn more about the words that are essential to know when classifying the largest Phyla of flowering plants.