CHARACTERIZATION OF PTERIDOPHYTES

The pteridophytes which include the ferns and fern allies such as the Selaginellas, Lycopodium, Isoetes, Equisetum etc. are characterized by the following features:

• The pteridophytes heralded the era of ‘vascular cryptogams’ on the earth as theyare the first group of plants ever evolved on the earth showing the presence of a well-developedvascular system named xylem for water and phloem for food transport respectively.Hence

• The xylem consists of mainly of a conducting element called tracheid, which are elongate narrow tubules with pores on lateral end walls, through which water passes from one tubule into another. On the other hand in the flowering plants the conduction is mainly through ‘vessels’ which are tubules connected end to end with their cross walls broken down to facilitate easier transport as if through a pipe.

• The phloem or food conducting tissue in pteridophytes also is of the primitive kind compared to that of the flowering plants.

• The reproduction of pteridophytes is mainly by spores and not seeds. The spores are a loose mass of powdery cells produced within special containers called sporangia of varied kinds.

• A group of ferns called ‘pteridosperms’, now represented by fossils, had very primitive kind of seeds. Hence the pteridophytes may be considered as a crucial link between the modern seed plants (the gymnosperms and angiosperms) with well developed vascular tissues and ancient land cryptogams, the bryophytes, without xylem and phloem and seeds.

• In the life cycle of every pteridophyte are two separate individuals, one a short living flimsy and small gamete producing one resembling a rootless, stemless, bryophyte without also organized vascular system and the other a larger plant, with a longer life span, differentiated often into roots, stems and leaves and reproducing asexually through spores. This dimorphism of plant body, of two totally different looking generations alternately appearing in the life cycle of the same species is known as ‘heteromorphic life cycle’ (Dudani et al, 2011).