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Some of the most important characters of Pteridophytes are as follows:
1. Habit:
All Pteridophytes are annual and herbaceous, e.g. Azolla, Selaginella but a few are perennial woody tree fern e.g. Alsophila, Angiopteris.
2. Habitat:
They are basically terrestrial plants grow in moist shady cool places.
3. Life Cycle:
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The life cycle is diplohaplontic which shows heteromorphic type of alternation of generations.
4. The sporophyte is the dominant plant body which differentiated into roots, stem and leaves.
i. Roots:
Primary root short lived and replaced by adventitious roots. But Psilopsids are rootless plants having rhizoids.
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ii. Stem:
Herbaceous or woody and branched.
iii. Leaves:
Leaves may be microphyllous (e.g. Lycopodium, Selaginella, and Isoetes) or megaphyllous. (e.g. ferns). The leaves bearing sporangia are called sporophylls. In some cases sporophylls for compact structures called cones or strobili (e.g. Selaginella, Equisetum)
5. Vascular tissues present throughout the sporophyte except in reproductive parts and in gametophyte. Xylem consists of tracheid’s (vessels and fibers absent). Phloem consists of sieve cells only.
6. Secondary Growth absent except in Isoetes.
7. The sporophyte produces meiosopres inside sporangia. The development of sporangia may be eusporangiate (from a group of cells, e.g. Selaginella, Equisetum, Ophioglossiim etc.) or leptosporangiate (form a single cell, e.g, Azolla, Marsilea, Pterium etc.)
8. The sporophyte may be homosporous (e g. Dryopteris) or heterosporous (e.g. Selaginella, Marsilea, Azolla etc.) In heterosporous forms, 2 types of spores develop i.e. microspores and megaspores.
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9. The spore germinates into an inconspicuous, free-living, photosynthetic thalIoid gametophyte called prothallus.
10. The gametophytes develop sex organs like antheridia (male sex organs) and archegonia (female sex organs).
11. Fertilization requires water for transfer of antherozoids to the egg of archegonium.
12. Zygote develops into embryo within the archegonial venter.
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13. Apogamy and Apospory: Sometimes deviation in the regular alternation if generations are noticed in the form of apogamy and apospory.
Apogamy is the development of an unusual haploid sporophyte from the gametophyte without the fusion of gametes. The cause of apogamy include ageing of the prothallus, failure of sex organ formation and normal fertilization, prothallus growing under bright light and high temperature etc. Natural apogamy is common in ferns like Dryopteris, Adiantum, Osmunda, Pteris etc.
Apospory is the development of unusual diploid gametophyte from the vegetative parts of sporophyte and not from the spores. The cause of apospory involves deficiency of mineral nutrition, development of leaves under dim light etc., e.g. Pteris, Nephrolepis, Drynaria etc.
