Life forms of Pteridophyta, their origin and evolution.

The following separation of the main growth forms of Pteridophyta is proposed: thin-rhizomatous, creeping-rosetted, ascending-rosetted, vertical-rosetted, and arborescent. Each of these can be divided into life forms according to a series of morphological and other characters. The most primitive growth form of Pteridophyta is acknowledged as the thin-rhizomatous. In the course of evolution toward polymerization and integration of fronds, the group of arborescent Pteridophyta were transformed into shoot plants, initially of the Cycas type. Water ferns (Salviniaceae) and seed ferns (Pteridospermae) are known as the arbitrary type of Lycopsida which did not reach the state of shot structure of the body. In this respect, Equisetales occupy an intermediate position. It may be assumed that in the evolution of plants, the change in their life forms was of paramount significance.