Notes on the Geological distribution of plant kingdom

It is considered that the plants appeared on this earth some times during the beginning of the Paleozoic era or even a little earlier.

This is evidenced by the occurrence of fossils of a few primitive plants in the sedimentary rocks formed at the start of Cambrian period.

The early ancestors of land plants came to live on this planet during Devonian and Silurian periods. The evolutionary process during this period was comparatively slow hence very few fossils are preserved in the rocks formed during this period.

At the start of the Carboniferous period the plant world evolved rapidly and towards Permian period they attained worldwide distribution. A major part of the land mass was covered with thick forests. The coal deposits and associated plant fossils stand evidence to the above fact.

In India, Glossopteris type plant fossils occur in abundance in the Lower Gondwana rock formations deposited during this periods. Glossopteris, Gangamopteris, Gondwanidium, Schzoneura are a few examples of pteridophytes which were predominating the Indian forests of Gondwana period while during the Upper Gondwana period the domim plant life was cycadophylicales, which include Ptilophyi Williamsonia, Otozamites type of plants. These are a few examples] plant fossils preserved in Gondwana rock formations.

Gradually the gymnosperms became extinct during the Cretaceous per and were replaced by more evolved angiosperms which spread worldwide and dominate the present day landscape.

Glossopteris:

Phylum – Spermatophyta, Sub-phylum – Gymnosperm

Class – Cycadofilicales, Genus – Glossopteris

The frond or leaf is generally large and ventricular in shape with smooth margin and acute apex. In length the leaf grow up to 30 to 40 cm with reticulated venation and prominent mid rib. It is associated with vertebraria type rhizome.

Geological age – Upper Carboniferous to Lower Triassic. Fossils are reported from Lower Gondwana formations.

Gangamopteris:

Phylum – Spermatophyta, Sub-phylum – Gymnosperm

Class – Cycadofilicales, Genus – Gangamopteris

The leaf is similar to that of Glossopteris in size, but with parallel venation and without a distinct mid rib. It occurs in association with Glossopteris and Vertebraria type rhizome in Lower Gondwana formations.

Geological age – Upper Carboniferous to Lower Triassic.

Vertebraria:

Phylum – Spermatophyta, Sub-phylum – Gymnosperm Class – Cycadofilicales, Genus – Vertetbraria

It is the root associated with both Glossopteris and Gangamopteris type of leaves. Its body appears to have made up of two rows of bricks giving a look of vertebral column.

Vertebraria fossils are reported from Lower Gondwana formations. Geological age – Upper Carboniferous to Lower Triassic.

Ptilophyllum.

Phylum – Spermatophyta Sub-phylum – Gymnosperm

Class – Cycadales Genus – Ptilophyllum

The compound leaf of this cycad bears small pinnules with entire margi acute apex and prominent mid rib from where veins are given off. The pinnules overlap on each other and their leaf bases are fully attached to the main rachis. In India, it is reported from all the Upper Gondwana formations.

Geological age – Jurassic to Cretaceous.