Taxonomy: Plants

All life on Earth is related, closely-- or remotely. All organisms have a common ancestor, which was a single celled organism, several billion years ago. When biologists study life, and classify the different species, it's called taxonomy. When you make a taxonomical division of species, it's based on how closely the species are related. In other words, how many generations we need to look back, to find a common ancestor.

Compare with your own family. If you have a sibling, you have the same parents, and are closely related. You and your cousins have the same grandparents, which is two generations back. So cousins are more remotely related than siblings. The more generations we need to go back to find a common ancestor, the more remote is the relationship.

It's the same with animals and plants, as shown by the way taxonomy divides them up. One way we commonly choose to categorise the plants on Earth is to sort them into two groups. In the first group there are.. Woody plants, including trees and bushes, Grasses, which include cereal food crops, like wheat and rice, and plants we use for lawns... And herbaceous plants, with softer stems, which include most leafy and flowering plants.

This first group of plants all reproduce by spreading seeds. They are called seed plants. The second group of plants includes Ferns and lycophytes. This group reproduces - not with flowers - but by emitting spores, which are very tiny and are easily spread by the wind. If you look under the leaves of a fern, you can see small dark patches.

These are collections of spores. These plants are spore plants, and they have existed on Earth longer than seed plants. All plants mentioned so far have in common that they have vessels that carry water and nutrients from the roots all the way to the leaves and flowers. They are vascular plants. There are also spore plants that don't have vessels.

These are various kinds of moss. Together, all these plants constitute the land plants on earth. If we make a taxonomical diagram, the 'tree' looks like this. -- The 'branches' show how the different groups of plants are related. The red dots show where to find the common ancestor. In this red ring we see all vascular plants.

In this blue ring we see all spore plants. -- But is this the whole family tree of plants? No. These are only the land plants on Earth. Together with green algae, that live in oceans and lakes, they constitute the green plants group. And green plants are one of three divisions in the plant kingdom.

The others are red algae and glaucophytes. As you begin to see, the taxonomy of plants is large and complex. You don't need to remember what the whole tree looks like, but it's important to know how it is constructed: Species are grouped with other related species. And several groups can be combined to form larger groups. A tree is formed, and at every junction we find a common ancestor.

This is how taxonomy works.