A species – the basic unit in nature

Moon jellyfish and lion's mane
jellyfish, two different species.
Drawing from Linnaeus journey
to the county Västergötland in 1747.

Something as evident as the fact that there are different species is nothing to brood upon, is it? Well, yes it is. Man has always used the species as a basic unit when classifying plants and animals. It is noteworthy that no one can really tell exactly what a species is. There are many different species definitions.

The view of species and their role in nature has changed through time. In Linnaeus’ time scientists were searching for the divine order in nature. It was harmonious, stable and was to be present in nature. The order we are searching for today is the result of a process through millions of years, the evolution. We will never know exactly how the evolution proceeded but we can draw conclusions by studying the plants and animals we find around us today.

A new species has to be described according to certain rules. It has to be given a scientific name. This name has to consist of two words according to the two names principle. The appearance of the species also has to be described and in what ways it differs from other closely related species. Linnaeus was the founder of the naming principles of plants and animals. This was one of his major contributions to science.

It is not easy to identify a species

Wood anemone and yellow anemone are two different species. It is easy to distinguish between them, for example on the flower colour, but it is not always easy to recognise different species. It is important to think about what a species is. How do we define a species, and what species definition should we use?

According to the traditional species definition a species should be composed of individuals similar to each other. Then the difference between species is that they look different. Humans look similar to each other, but show no close resemblance to chimpanzees, which belong to another species.

This species definition seems to work well, but when studying nature closer it becomes obvious that it is not always that simple. There are for example groups of individuals that superficially are very similar to each other but seem to be different species when studying their chemistry.

According to another species definition all individuals within a species should be able to interbreed and have fertile offspring. The problem then is that some groups are composed of individuals similar to each other but which cannot interbreed at all. Should then each individual be called a species?

No matter how much scientists try to find a good species definition, there is none that can be used for all groups of organisms. Therefore, there is always an active species definition debate going on among scientists in Systematics.

How to describe a new species

Tortoise shells from Linnaeus’ collections in London.
Photo: Hans Odöö.

All the time new species are discovered. They have to be described and given scientific names. The names are then used in many different ways by people who work with plants and animals. It is therefore very important to know exactly which plant species each specific name is tied to.

The name of the new species has to be published in a scientific journal. To show exactly what plant or animal the name refers to, a reference to a collected specimen of the species, a type specimen, is given. Even though the author of the species always tries to make an accurate description of the species, it is important that other scientists can see the specimen with their own eyes. The type specimens are kept in scientific collections in museums.

In the past there was no rule about type specimens. Linnaeus described thousands of species without telling what individual he had looked at. To be certain of what he meant some detective work has to be done to try to find out what specimens he had studied. Often the answer is found in Linnaeus’ own collections of plants and animals, or other collections he had studied. Most of those collections are today found in London, but also in the herbarium (plant collection) of the Swedish Museum of Natural History and in the Zoological Museum at Uppsala University.

Each species has two names

All known organisms have scientific names. The wood anemone is named Anemone nemorosa and the elk is named Alces alces. The scientific names might feel more difficult to learn than the native names, but they are easy compared to the names used in Linnaeus’ time. They could be very long and consist of a long string of Latin words describing the plant or animal. The wood anemone was then called Anemone seminibus acutis foliolis incisis caule unifloro, which means: anemone with pointed seeds, leaves with incisions and stalk with one flower.

The sabre fish pictured in Linnaeus’ journey to Scania 1751.

Linnaeus was not happy with the long names. In the account of his journey to Scania he writes about a fish, the sabre fish, which had been given a name longer than the fish. The scientific name of the fish consisted of no less than 63 words!

Since Linnaeus had the talent to simplify and rationalise, he figured out a much better system for naming organisms. In the book Species Plantarum he used, for the first time, his new naming system throughout the whole book. This book had all known plants of the world listed following the sexual system. Linnaeus introduced the two names principle, the binary nomenclature, in Species Plantarum. The binary nomenclature means that each species has a genus name and a species name. The genus name of the wood anemone is Anemone, a genus name common to all closely related anemones. The species name of the wood anemone is nemorosa, and that of the closely related yellow anemone is ranunculoides (Anemone ranunculoides).

By the two names principle of Linnaeus, short and useful working names for the plants were introduced. The new names became very popular, not least among the student who had to learn them by heart. Linnaeus introduced the same principle for the names of animals in 1758, in the 10th edition of Systema Naturae. It was an ingenious rationalisation that is still used. The system with a genus name and a species name is used worldwide and is one of Linnaeus’ most important inventions.

Scientific names

All species have scientific names. What use is there to learn that wood anemone is also called Anemone nemorosa?

Imagine taking a walk in a beautiful forest with a Swedish friend and you want to tell him or her how beautiful the forest is in the spring with the wood anemone colouring the ground white. Wood anemone is called ”vitsippa” in Swedish, which of course you do not know, but if both of you know some scientific names of plants you can talk as much as you like about the beauty of nature.

The twinflower (Linnaea borealis)
is called linnéa in Swedish. Here
from a Japanese flora.

In books about animals and plants the scientific names are most often included, in whatever language the book is written. This makes us able to read a flora in Japanese or Russian and be sure that the picture shows a wood anemone. The scientific names help people from different countries to communicate. One will not reach far only knowing for example Swedish. There are 250 000 species of flowering plants in the world, but only about 5000 of them have Swedish names.

Scientific names are often called Latin names, however many of the names have a Greek origin, for example from Greek mythology.

To name a new species

Water-violet, Hottonia palustris.
Photo: Karin Martinsson.

Each species has to have a unique scientific name. How does one decide the name for a new species? The most common way is to try to give it a name that tells something about the plant. For instance how it looks, where it grows or when it flowers.

Water-violet that grows in still water is called Hottonia palustris. The species name palustris means ”growing on wetland”.

Mistle thrush, which lives of mistletoe berries, is called Turdus viscivorus. The species name viscivorus means ”mistletoe eater”.

Linnaeus named many plants after well-known botanists. Sometimes he compared the plants to the persons:

”The Dillenia has the most magnificent flower and fruit among the herbs, just like Dillenius is a magnificent phenomenon among the botanists.”

It still happens that scientists name species after persons they want to honour, for example prominent scientists or teachers. It is also common that the person who first found a plant has in named after him or her. Whatever name a plant has, it is always exciting to translate the name and try to figure out why it got its name. Do you know a plant called Linnaea borealis and why it is named as it is?

Linnaea borealis

The twinflower grows on soft moss in dark spruce forests. It has small, pink, bell-shaped flowers with a delicate scent of vanilla. It is one of the most loved plants in Sweden and a popular decoration on porcelain, tablecloths and paintings.

Photo: Börge Pettersson

But how did the twinflower get its Latin name Linnaea? Did Linnaeus discover it? No, the plant was known since the 16th century. It was then thought that it was a kind of bellflower and it was called Campanula serpyllifolia. The twinflower was Linnaeus’ favourite plant and he really wanted it to be named Linnaea, but botanists never named plants after themselves so he needed help by someone who could name it after him.

The solution to the problem turned up when Linnaeus lived in the Netherlands to take his PhD. There he made friends with the famous doctor and botanist Gronovius. He helped Linnaeus economically and in many other ways. He also gave the name Linnaea to the frail little plant. Linnaeus was very satisfied and he himself added the species name borealis, which means ”from northern areas”.

Last modified: 2021-11-25