Introduction to the Pteridophytes

The Bryophytes are a group of simple land plants which in many ways are an evolutionary dead end. They probably evolved from the green algae at about the same time as the first vascular plants. Like them they are "Embryophytes" with multicellular sex organs but they do not have vascular tissue like Rhynia and its relatives. 

The first vascular plants rapidly diversified to cover the earth. The sporophyte was the dominant phase of the life cycle of these early Pteridophytes. Unlike the Bryophytes, these plants are in the mainstream of land plant evolution and eventually gave rise to the seed plants. 

Let's look at the main groups of Pteridophytes!

The ferns are largely tropical and represent 97% of living Pteridophytes. 
 
 

Most of this group is extinct. Lycopodium is the sole surviving genus.

Selaginella is the sole surviving genus of this group. 

There are no horsetails in the Caribbean. 

Before we look at the existing ferns and fern allies you should realize how important and common these plants once were.

About 300 million years ago, in an era called the Carboniferous (literally "coal-bearing"), the fern allies dominated the earth. Unlike today's herbaceous fern allies, however, these plants were huge. 

In fact, these were the first trees of the earth. At that time much of the land (the continents were still clustered together as one land mass!) had a warm, tropical climate. These giant club mosses and spike mosses and horsetails thrived in the vast swamps that stretched throughout this landscape. 

In this swampy habitat, the land was alternately sinking and the waters silting up with river sediments. Plants would be covered by water then by silt without rotting properly. The layers upon layer of sediment would compress the dead plant material. Over millennia this resulted in the formation of coal and natural gas as well as some beautifully preserved impressions of plants in coal. The magnitude of coal mining around the world has meant a comparatively large number of plant fossils have been described from this period.   

A word about plant fossils... 

The study of fossil plants - palaeobotany - is a very specialised area of research. Fragments of plants are given generic names based on their resemblance to other plants. Whole plants - leaves, stems, spore-bearing regions - are not usually found together. It must then be deduced whether leaf A and stem B are actually part of the same plant. Have a look at these two fossil plants to understand how a picture of the plant is pieced together from such fragments;- 

Lepidodendron was a giant club moss tree some 30 m tall. When you have looked at it, go back to the picture of its living relative Lycopodium and see if you can see the resemblance.  

Calamites was a giant horsetail relative, resembling a Christmas tree! When you have looked at it, compare the pictures of its living relative Equisetum and see if you can see the similarities.