Quick Notes on Fossil Gymnosperms | Botany

Quick Notes on Fossil Gymnosperms!

Fossil Gymnosperms :

Class-Cycadopsida

Order-Pteridospermales

(Cycadofilicales):

The Ptieridospermae or the Cycadofilicales are fossilized plants that first appeared in the upper Devonian. They were very common throughout the Carboniferous and extended upto Permian strata. After the Permian they began to decline and disappeared altogether. It is in the early Devonian rocks that the members of some very primitive type of land plants disappeared.

These plants were probably the simplest pteridophytes.

They had no roots, some without leaves and some had small tiny outgrowths which represented the leaves. This primitive group of land plants was different from pteridophytes. Their stem had well formed xylem and phloem tissue and the tips of the branches bore sporangia on them.

It is from the Upper Devonian through the Carboniferous and upto end to some extent into Permian strata also that we come across with a large number of fossilized plants belonging to Bryophytes, Pteridophytes and Gymnosperms.

The Carboniferous strata is very rich in plant remains. It appears that in those times the whole surface of earth was covered up by very extensive and luxurious forests. It seems that the climate in those times on the whole surface of earth was very uniform.

This view is based because identical fossils have been found in very widely separated areas. It appears that during this Carboniferous which is also described as coal age there were general and .sudden changes in the topography of earth.

It appears that very extensive forests got submerged and it is the submerged forests from which we get the extinct coal supply of present day. During this Carboniferous which has been sometimes described as age of ferns, very large sized Lycopods and Equisetales were common.

Along with these fossil pteridophytes, there were also present seeded plants which developed seeds of Cycadian type on them. Those plants which bore seeds were formerly described as Cycadofilicales. English workers (Oliver and Scott) described them as Pteridosperms while American workers call them Cycadofilicales.

These seeds were known to previous workers also but their association with fern like leaves was recognized in 1903. It was during this year that some of these Carboniferous seeds were found in organic continuity with the leaves of fern like plants.

These seeded fossil plants have definite relation with gymnosperms of which American workers think they form an extinct class. They show definite relationships with ferns on one side and cycads on the other.

They were distinctly spermous plants for their seeds were not enclosed in closed carpel as in angiosperms. This group of seeded plants was dominant during Carboniferous, they probably began in the Upper Devonian and began to decline in the Permian after which they disappeared altogether.

They were very widespread. They have been found in all countries in Northern Hemisphere and in Southern Hemisphere also they have been found wherever they have been searched for.

One of the best known plants is Lyginopteris which is best known of all Carboniferous plants. Before 1903 different parts of the plants were known, their stems, roots, leaves and also the seeds. On the whole surface of seeds capitate glands were present and it was the presence of these capitate glands that gave rise to idea that all these different parts of plants might be of one or same plant.

Later on the entire plant was found in one place in organic continuity from roots, stems and leaves.

A number of stem genera have been described from time to time. These stem, genera may be grouped under a number of families. The more important families are Lyginopteridaceae, Medullosaceae, Calamopityaceae, Peltaspermaceae and Corystospermaceae.

Pant (1957) makes a distinct class Pteridospermopsida for these plants. He divided this into six orders. These orders are Lyginopteridales, Medullosales, Glossopteridales, Peltaspermales, Corystopermales and Caytoniales.