Evolution of plants; part 1.

As you are no doubt aware,the plant kingdom is split up into different groups and these are based on similarities and differences but largely represent an evolutionary line, so that some groups are more primitive and others more advanced.

I think it is interesting to know something about these groups, especially to have some idea as to the relationships between them. Over the years much effort has been put into classification and even with modern DNA analysis there is still much to be discovered and argued about. Part of the problem is that the species alive today originated many years ago and present day species do not represent a continuous line of evolution. Important links have become extinct and even fossil records may not have been found or even exist. There would have been common ancestors which may well have died out and even with the addition of fossil evidence there are still ‘missing links’ so that a generalised view is possible but some gaps exist and a few of these gaps are quite large.

Before we start, if you click on the highlighted text which is in red then it will take you through to a page specifically about that subject.

Roughly speaking we can split the plant kingdom into  groups.

Algae, these are quite primitive and largely aquatic but having said that some like the ‘brown seaweeds’ have developed to a reasonably complex level. This is one of our largest  brown seaweeds called Laminaria digitata  also sometimes called Oarweed.

 

 

 

 

Bryophytes, these are the most primitive of land plants and are represented by two groups, one we have all heard of – the mosses, and another group that are maybe less familiar called liverworts. It is likely that the Bryophytes evolved from some distant algal ancestor but there are no obvious intermediates or fossils to back this up. The light green plants in the center are Liverworts and the darker green are mosses.

 

 

Pteridophytes,  Pterido sounds primitive, like pterodactyl, although Pterido  is Greek for fern. These are a group of plants which reached their peak in the Carboniferous period, but are still quite common, but less dominant, today. The main group that everyone has heard of is the Ferns, and these are the most primitive of the group.

There are others which whilst  not so common and less familiar are non the less quite important in providing a nice evolutionary time line from this group through to the next group called the Spermatophytes. They are the Horsetails,  Sellaginellas, and Lycopodiums or Club mosses.

However what is not really known is the link between Bryophytes and Pteridophytes. There are some similarities but there are no intermediate forms suggesting that they were both derived from a common ancestral group but that was way back and it could be that they both evolved from some advanced form of algae.

Spermatophytes, not to do with sperm, but from the Greek for seed and then phyte for plant so plants that produce seeds.  This huge and advanced group all produce seeds, whereas the previous groups all produced spores. The lineage is fairly easy to follow and the most advanced Pteridophytes show many similarities with the most primitive Spermatophytes called the Cycads, and the Ginkgo Tree.  After these species the group is split into two major sub groups, known as the Gymnosperms and Angiosperms. Putting it more simply, the conifers and the flowering plants. But getting back to the scientific names, Gymno means naked so the seeds do not have a coating. and Angio means flask so the seeds are contained and protected in a container.

Please be aware that the flowering plants represent a huge group which includes many plants that a non botanist might not recognise as having ‘flowers’, ie all the grasses, sedges and rushes, which do flower and they give me hay fever from their pollen, but their flowers are not pretty. The other vast group are the trees and bushes which are wind pollinated like Oak, Ash, Beech and Hazel, to name just a few.

The flowering plants are the pinnacle of evolutionary development, at the moment , however I assume this is not the end point of evolution, unless the world goes bang tomorrow. Evolution has always occurred and no doubt will continue.  In several million years there will probably still be flowering plants growing on earth but rather like the ferns of today they may well be a small surviving population, the future representatives of what is here today. Possibly from what we know of evolution the flowering plants will not necessarily develop into the next new plant group, in the same way that mosses did not evolve directly into ferns. Rather there will be some ancestor of the flowering plants which will branch out and develop some new and successful features so that the Attenboroughs of the distant future will look back and say ‘Yes, some form of Cycad was responsible for the development of today’s dominant species and the flowering plants were just an off shot of evolutionary development….. Who knows?

PS I realise that in several million years humans and thus Attenborough’s will probably be extinct and some new animal species will rule. Having said that Attenborough seems to be going on for ever so it could be him.

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