Pteridophytes are the primitive tracheophytes. They are the non flowering vascular cryptogams with conducting tissues namely xylem and phloem. These plants produce definite embryos during the lifecycle, but they are not developed within definite seeds. Hence, pteridophytes are regarded as seedless vascular plants or seedless embryophytes. They are more than 400 genera and about 10,500 species of pteridophytes. They include club mosses, horse tails and ferns.
Characteristics of Pteridophytes
1. The plant body is a sporophyte, with true stem, leaves and roots. Plants show distinct alternation of generation, diploid sporophyte alternate with haploid gametophyte. The root, stem and leaves have vascular tissues xylem and phloem. Xylem is a water conducting tissue and phloem is a food conducting tissue. But the xylem lacks true vessels and phloem lacks companion cells. Sporophytic plant reproduces by spores produced inside sporangia borne on leaves(leaves) usually on the ventral surface. In some pteridophytes, there are two types of leaves, smaller microsporophyll's and macrosporophylls. The sporophylls are uniformly distributed or aggregated to form compact cones or strobili at the stem tips. In higher pteridophytes, the sporangia are present in well organized groups. Spores are haploid developed after meiosis in sporangia of sporophyte. Many pteridophytes are homosporous and most terrestrial ferns are heterosporous which produce microspore and macrospores.
2. In homosporous plants, the spore germinate and give rise to small, multicellular free living, photosynthetic, thalloid gametophyte called prothallus. In heterosporous plants the megaspores and microspores give rise to female and male gametophytes respectively. These gametophytes require cool, damp and shady place to grow. The antheridia produce sperms. They are released from the antheridia, to the mouth of archegonia with help of water which results in fertilization. The female gametophytes in these plants are retained on the parent sporophytes for variable period. This event is a precursor to the seed habit considered an important step in evolution.