General characters of Pteridophytes:
1. HABITAT
Pteridophytes grow under varied habitats. Most of them are terrestrial plants and thrive well under damp and shady conditions while some flourish well in open grasslands, exposed dry places or even under xeric conditions e.g. Selaginella, Lepidophylla. A few are aquatic e.g. Marsilea, Azolla, Salvia, while others are epiphytes e.g Lycopodium oregana, Psilotum flaccidum.
2. SPOROPHYTE
The main independent plant body is a sporophyte developed from diploid zygote after fertilization of gametes. It shows great variations in form, size and structure. Most of the present day pteridophytes are herbaceous except a few woody tree ferns e.g. Cyathea spinulosa, Diksonia.
3. MORPHOLOGY
Plants are differentiated into true roots, stem and leaves, however in lower pteridophytes like Psilotales and Psilophytales leaves and roots are absent. Plants exhibit dorsiventral or radial symmetry and branching of stem is dichotomous or monopodial, bearing microphyllous e.g. Lycopodiom, Equisetum or macrophyllous leaves e.g. Pteris, Petridium. Primary root is short lived and is replaced by adventitious roots, which arise endogenously.
4. ANATOMY
(i) All the vegetative parts possess vascular tissue organized in definite groups or stele which ranges from simple protostele e.g. Selaginella, Siphonostele e.g. Marsilea, to dictyostele e.g. ferns to eustele e.g. Equisetum. Xylem mainly consists of tracheids and xylem parenchyma.
(ii) Vessels are absent. However in Selaginella, Marsilea and Equisetum some primitive type of vessels have been reported. Phloem consists of sieve tube and phloem parenchyma.
(iii) Companian Cells are absent, secondary growth does not occur in most of the pteridophytes, except in Isoetes.
5. REPRODUCTION
(1) Sporophytic plant body reproduces by producing haploid spores by meiosis inside the sporangia and serve as a means of asexual reproduction. (ii) The plants may be homosporous (e.g. Psilotum, Pteris, Equisetum) or heterosporous (e.g. Selaginella,Marsilea). The development of sporangia may be eusporangiate (e.g. Selaginella, Lycopodium from agroup of initial cells) or leptosporangiate (from a single initial cell, e.g. Marsilea, Pteris).
(ii) There is a great variation in the distribution of sporangia. Sporangia are either borne on stem (Cauline in origin) or on Leaves (Foliar in origin). The latter are called sporophylls, which may be scattered on the plant or restricted to a particular region called strobilus or cone or produced in specialized structures called sporocarps.
6. GAMETOPHYTE
(Spores germinate to produce haploid gametophyte, called prothallus, which is markedly dissimilar from the sporophyte. The homosporous pteridophytes produce bisexual (monoecious) gametophytes (may be protandrous or protogynous) whereas heterosporous ones produce unisexual (dioecious) gametophytes.
(ii) Microspores and megaspores produce male & female gametophytes respectively. The latter may be exosporic (Psilotum, Lycopodium, Pteris), grow on the soil as independent plant or endosporic, grow for the most part inside the spore wall e.g. Marsilea, Selaginella.
(iii) The prothalli from homosporous ferns are either green and simple or branched and aerial structures (e.g.Pteris & Pteridium) or they may be subterranean, colorless, tuberous and saprophytic (e.g. Lycopodium),
(iv) The gametophytes are highly reduced in heterosporous sporophytes represented by a few vegetative cells and sex organs get their nourishment from the reserve food stored in spores.
7. SEX ORGANS
(1) The sex organs may be embedded (Lycopodium, Equisetum) or projecting type (Pteris, Pteridium) andresemble the bryophytes in general plan of structure.
(i) Archegonia, the female sex organs are flask shaped differentiated into venter and neck. Venter containsventer canal cell and egg. Neck consists of 2-6 vertical rows of cells and an axial row of 1-14 neck canalcells.
(iii) Each antheridium, the male sex organ consists of single layer of sterile jacket enclosing a large number of androcytes, which metamorphose into flagellate motile antherozoids.
8. FERTILIZATION
Sexual reproduction is oogamous and fertilization occurs in presence of water, as it is needed for dehiscenceand movement of antherozoids to archegonia. It results in the formation of diploid zygote, which develops into an embryo within the archegonial venter and
9. SYNGAMY
It results in the formation of diploid zygote, which develops into an embryo within the archegonial venter andis surrounded and nourished by the prothallus tissue in early stages of developments.
10. Alternation of Generation in pteridophytes is heterogamous and life cycle is diplohaplontic.