The pteridophytes are classified into fallowing four classes
Class: Psilotopsida
1. The class includes both fossil and living forms.
2. Plants are sporophytes. It is simple and dichotomously branched without leaves and roots.
3. The sporophytes have underground rhizome with unicellular rhizoids. The arial branches are flattened or ridged with scale like appendages in the upper portion only. The arial stem bears many trilobed synangia in triads on a minute stalks in the axils of the scale leaves.
4. Gametophyte is a microscopic, brown coloured and saprophytic subterranean structure. It is irregular cylindrical, some what dichotomously branched structure covered with unicellular rhizoids, antheridia and archegonia.
Example: Psilotum
Class: Lycopsida
1. The plant body exhibits root, stem and leaves. Roots are adventitious. In selaginella they develop special downwardly growing structures called rhizophores. The leaves are small with one vein in each leaf.
2. The mature sporophyte has cones or strobili at the ends of shoots. Each strobilus carries many small leaves called sporophylls.
3. Members are either homosporous or heterosporous.
Example: Selaginella
Class: Sphenospida
1. The body has root, stem and leaves.
2. The horsetails have ribbed articulated stem with whorls of branches and whorls of scale leaves.
3. The stems are jointed at the nodes and the internodes are hollow. The nodes bear scale leaves in whorls.
4. The spore producing bodies are borne at the end of branches and resemble the horsetail. The sporangia are usually borne in groups on a special structures called the sporangiophores. They are arranged in whorls at the tip of branch to form a distinct cone(strobilus).
Example: Equisetum
Class: Pteropsida
1. The sporophytes have underground stem called rhizome, adventitious roots and aerial large leaves called fronds.
2. The leaves are arranged spirally with branched veins. The leaf is usually differentiated into petiole and rachis bearing dissected leaflets. Young leaves show cercinate vernation.
3. Morphologically, the sterile leaves and sporophylls are alike and they never form any cone or strobilus.
4. The sporangia are borne in groups forming sori, either on the margins or near at the centre on the lower surface of the sporophyll as brown dots covered by false cover called inducium.
5. Gametophyte is produced by the germination of spores. It is light green, flat, thin dorsiventral differentiated heart or cordate shaped structure. The antheridia and archegonia are present on the ventral surface.
example: Pteris