We have looked at the ways in which plants first colonized the land surface of the Earth, but perhaps it is time to look at the evolution of plants as a whole in more detail.
It is generally easier to follow the trends in the evolution of plants because modern advanced plants may be quite similar in their make up to a more primitive form. Animals and the development of the animal kingdom are very much more complicated.
As has already been mentioned, plants are made up of cells. These cells are the living substance from which all life is composed. It is unnecessary here to discuss the detailed organization of living cells. It is enough to say that they are made up of a dense nucleus surrounded by a watery fluid. The very first plants, of course, were probably just single cells of living matter.
Bacteria are sometimes thought of as plants. These are tiny (microscopic) single-celled organisms which usually live by feeding on other plants or animals as parasites, or on dead or decaying matter. It has been discovered however, that there are bacteria that will even feed on such unpalatable things as concrete and glass.
In fact, without bacteria, no other life would be possible, because it is bacteria that aid in the breaking down of rock debris to form soil, and bacteria that enable waste products to decay. As you might expect, fossil remains of bacteria are rare, although they can be found in the rock called the Rhynie chert of the Scottish Devonian.
The algae are also a very primitive group of plants, still in existence today, but representing some of the earliest life forms to be found on Earth. The algae are the most diverse plant group both in size and in their ways of life. Remember that seaweeds are algae as is the green film that forms on the glass of a goldfish tank.
The evolution of plants can usually be traced on the basis of their way of multiplying, and the algae are no exception. Their method is very primitive. At a particular time of the year the cell contents become denser, two cells come together, and new nuclei develop. The rest of the year the cells just divide.
Algae are usually subdivided into groups on the basis of their colour. Green algae are those that can only live in clear, comparatively shallow, marine conditions and they build reefs. Red algae include the seaweeds and live in the deep seas making use of only part of the light that is found at depth. The blue-green algae are thought to be important in the formation of soils. The brown algae live in shallow water marine conditions.
What is the Importance of Plants in Life’s Framework?
It is only when we stop to think that we realize the importance of land plants to us. We eat them in our cereals and vegetables, we make use of them for fibres like cotton, we depend on them for many drugs such as penicillin, and as we have already mentioned we need the fossil fuels.
But even when already mentioned we need the fossil fuels. But even when we eat meat, we must remember that the animals which produce the meat probably lived on plants.
Plants are nature’s producers. From sunlight, oxygen, and other foods from the soil, plants manufacture the foods upon which all animals ultimately depend. It is worth noting that it was with the rise of the land plants in the Devonian, that land animals also began to evolve.