Introduction
The division Pteridophyta is the most advanced group of plants among the cryptogams. Their vegetative body can be differentiated into roots, stems, and leaves. In contrast, the other cryptogams, Thallophyta and Bryophyta, do not have a vegetative body that can be divided into roots, stems, and leaves. The division Pteridophyta comprises a large group of autotrophic green plants and forms one of the four main divisions of the plant kingdom.
Characteristics features of Pteridophytes
1. The pteridophytes plant body represents the sporophyte. In the life history of pteridophytes, both the sporophytic and gametophytic generations are independent of each other. Although in Pteridophyta, sporophytes are nutritionally independent of the gametophyte still they are dependent on gametophyte for a short embryonic period,
2. Plant bodies are provided with well developed true roots (exceptions: fossil Pteridophyta and Psilotum), stems and leaves. Stems and roots have apical growth. Roots are provided with permanent growing point and can grow in length indefinitely
3. Reduction of photosynthetic tissue ie., chlorophyll bearing cells remain mainly within the leaves- hence photosynthesis is also restricted to leaves which are provided with epidermis having stomata and chlorophyll bearing cells.
4. Sporophytes show well marked tissue differentiation-roots, stems and leaves are traversed by vascular Le, conducting tissues such as xylem and phloem-hence pteridophytes are also known as vascular cryptogams.
5. The sporophytes are also known as asexual or spore-producing generations. In Pteridophyta this generation may be either homosporous i.e. bearing one kind of spores which on germination give rise to gametophytes bearing both male and female sex organs (i.e. monoecious or homothallic), or heterosporous where spores are of two kinds-viz, smaller microspores and larger macro or megaspores. Microspores on germination produce male gametophytes while macro or megaspores on germination give rise to female gametophytes-hence heterosporous pteridophytes always produce dioecious or heterothallic gametophytes.
6. Spores are produced within sporangia-in homosporous types, sporangia are of one kind as spores are alike, but in heterosporous types sporangia are of two kinds viz. microsporangia (microspore containing sacs) and macro or megasporangia (macro or megaspore containing sacs). Sporangia bearing leaves are called sporophylls-in heterosporous pteridophytes sporophylls are also of two types viz., microsporophylls (microsporangia bearing leaves) and macro or megasporophylls (megasporangia bearing leaves). Sporophylls in many cases do not differ from the mature foliage leaves and are loosely arranged (some species of Lycopodium, ordinary ferns like Polypodium, etc.); in other cases sporophylls are specialised and localized to form compact structure known as strobilus (plural: strobili) or cone. 7. Stem and roots of the plant body i.e., sporophyte are provided with stele-a central vascular cylinder of conducting systems