Division : Pteridophyta (Pteron = feather; phyton = plant)
The Pteridophytes were the first vascular plants on the land are hence considered as the first successful terrestrial plants with true roots, stem and leaves. The group has about 400 genera and 10,500 species. The plants consist of pinnate (feather like) leaves. The Pteridophytes are also known as vascular cryptogams. These plants have a primitive conducing system and they are the only cryptogams with vascular tissue. They do not produce flowers, fruits and seeds. The late Paleozoic era is regarded as the age of Pteridophytes.
The Pteridophytes are terrestrial , small, either annual or perennial and grow luxuriantly in moist and shady places. e.g. ferns. They may be aquatic (Azolla, Marsilea), xerophytic (Equisetum) or epiphytic (Lycopodium) i.e. growing on large trunks of trees.
The pteridophytes show heteromorphic alternation of generations in which the sporophyte is diploid, dominant, autotrophic, independent and is differentiated into root, stem and leaves. The primary root is short-lived and is soon replaced by adventitious roots while the stem may be aerial or underground.
The leaves mat be scaly (Equisetum), simple and sessile (Lycopodium) or large and pinnately compound (Ferns).
In pteridophytes the xylem consists of only tracheids and phloem consists of sieve cells only. Secondary growth is not seen in Pteridophytes due to absence of cambium.
The sporophyte shows asexual reproduction and produces spores by meiosis from which the gametophyte develops. Gametophyte is haploid recessive but independent and reproduces sexually . Product of sexual reproduction, i.e. zygote produces diploid sporophyte.
Pteridophytes are of two types. Some are heterosporous; producing two different types of spores-small microscope and large megaspores. while many are homosporous producing only one type of spores. Spores are produced in special multicellular structures called sporangia.
The Pteridophytes, apart from normal way of reproduction, also sometimes show following methods;
1. Apogamy :
It is the development of the sporophyte without the fusion of the male and female gamete. It arises directly from the gametophyte. Here the sporophyte is haploid.
2. Apospory :
It is the development of the gametophyte from any cell of the sporophyte other than the spores. Such a gametophyte is diploid in nature.