Taxonomy basics (part 1): What is it, and why do it?

Metaphorically speaking, people like to put things in boxes. It's human nature to catagorize things, and plants, animals and fungi are no different. Besides being human nature, it's also a useful tool to help describe something to anyone from any background - for example you might want to describe a leopard on the African savannah. You could try to tell someone that it's a large cat with spots, but a general description such as that won't tell them exactly what it was. If you gave them a species name, in this case Panthera pardus, they would then be able to look up exactly what you meant. This is because of the way species names (often called 'latin' or scientific names) work, with each two-part (binomial) name unique to the species you're trying to describe.

The naming system we currently use was created by Carl Linneus in 1735. Names are typically written in two parts (although there is a whole set of different levels which I'll run through later), with the first word describing the group that species belongs to, and the second the actual species it is. The first part is known as the genus name, and in the case of the leopard it is Panthera, along with jaguars, tigers and lions. So the information you get from the genus is the sort of species it is, and what it is closely related to. Once it's been used the first time the genus name is often abbreviated to the first letter, which abbreviated or written in full, is always capitalised. The whole name should also be written in italics or underlined (it's just the convention that is followed, so it's clear exactly what is the species name).

The second part of the name is the unique name of the species itself. This tells you exactly what your species is, in the case of the leopard it is pardus, which distinguishes it from the jaguars, tigers and lions that make up the rest of the Panthera genus. So in full its binomial name is Panthera pardus, telling you it's a big cat with spots that lives in Africa.
Or is it?

There are other levels of classification in addition to the genus and species levels. There are broader groups, such as family, or even kingdom, and there are also some other lower levels that might include subspecies, breed, or in plants variety or cultivar. These last few are all the same species, they're just different forms of the same species, and they should be able to reproduce with eachother to produce viable offspring. For example going back to the leopard, there are a couple of sub-species you might have. P. pardus sub. pardus is the African leopard, however the International Union for the Conservation of Nature (ICUN, the big-boys in validating species internationally) currently recognise 9 subspecies of leopard, with another 2 possible subspecies described from skulls. These include subspecies from South-East Asia, China, India, Russia and the Middle-East. However in theory as they're only subspecies and may look a little different, if you stuck a Javanese and an African leopard together, they should still be able to breed and create fertile offspring.

Confused? I'll put in the heirachy now then, and use a plant-based example this time, we'll make it the... Sunflower (Helianthus annuus) :)

Kingdom: Is it a plant, animal, fungi, or bacteria? Plant
Phylum: If it's a plant, is it a flowering plant? Seed plant? Seedless vascular plant? Flowering plant (angiosperm)
Class: Be more speciefic? it belongs to the Asterids, a very species-rich group of plants.

Order: Asterales - they have many little flowers clustered together to produce one large 'flower' like inflorescence
Family: Now we're getting to the other closely-related species, it belongs to the Asteraceae family, a group of plants with daisy-like flowers.
Genus: Helianthus - this tells us what it's closest relatives are :)
Species: annuus - tells us exactly what it is

(then there might be subspecies and cultivars or even hybrids listed here)


The other useful thing about two part names is that it allows the actual species name to be re-used. For example people like to name species after other people, so if you get someone famous like Sir Joseph Banks, you end up with a bunch of species named after/in honour of him. So you might have a plant with the species name banksii (for example Banks' Grevillia, Grevillia banksii) but also animal species like the Red-tailed Black Cockatoo (Calyptorhynchus banksii) and the binomial name allows you to differentiate the two because the plant and the cockatoo will have different genus names. Clever eh? It also means our imaginations are not taxed as heavily, as I suspect the number of species in the world would far outweigh our creativeness at naming them ;)

Usually the names you'll see written down will be from Family level down (you can tell it's a family name in botany if it ends in 'ceae', or in zoology if it ends in 'idae'), and in botany at least you should mention who named the species the first time you write the name out in full as well (it allows people to look it up/refer to it etc). Often with plants you'll find the genus and species name, followed by the family name in brackets e.g. Helianthus annuus (Asteraceae). The use of family level ID is good, as it allows you to either see how weird your species is (such as the one that is the subject of my PhD, Cassytha pubescens (Lauraceae) as it is the only Lauraceae that looks and behaves like that) or to look up what it is related to quickly and easily.

So now we know how to write out a descriptive species name and why to do it, the remaining obvious question is how? How do you decide what is a species? And as that's a question with a rather chunky answer, I'll put that in a fresh post later ;)