|In this course we are going to use the term Pteridophyte to refer to non-seed
vascular plants, i.e. plants with xylem and phloem whose dispersal relies on spores not
seeds. (Be aware that some people use this term just to refer to ferns.)
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!
|Ferns||Club mosses||Spike mosses||Horsetails|
|This is a Caribbean tree fern, Cyathea arborea.
The ferns are largely tropical and represent 97% of living
|This is Lycopodium cernuum, a Caribbean club moss.
Most of this group is extinct. Lycopodium is the sole surviving genus.
|This is Selaginella serpens, a Caribbean spike moss. Selaginella & Lycopodium
are similar & some people call both club mosses!
Selaginella is the sole surviving genus of this group.
|This is the top portion with spore-bearing cone of a horsetail, Equisetum sp.
There are no horsetails in the Caribbean.
|Unlike the ferns, which are a highly successful, flourishing group, the fern allies
(as we call the other Pteridophytes) are virtually living fossils. Most of their relatives
have long since become extinct.
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.
Click on any of the sites below, to go back in time and visit these carboniferous swamps:-
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.
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.
|The Carboniferous was the age of the ferns and fern allies. The climate changed and these vast swamps dried up. These large "water-guzzlers" were ill-suited to the new drier habitats and became extinct. In fact, the only relatives of these first trees that survive today are all small herbaceous plants.|
now completed our introduction to the Pteridophytes.
Click the button to get started on this group by looking at the ferns.
C.M. Sean Carrington, June 4 1998