Pteridophytes

The division Pteridophyta includes a group of primitive vascular plants, commonly called pteridophytes. The adult plant body in these plants is a sporophyte. It shows differentiation into true roots, stem and leaves. The stem is mostly herbaceous. Leaves may be smaller or larger. Vascular tissues are present in all the vegetative parts of the plant body.

Reproduction involves production of spores inside special structures called sporangia which occur on the ventral surface of fertile leaves called sporophylls. Sprangia may sometimes be found in groups called sori.

The plants may be homosporous - producing only one type of spore or heterosporous - producing two different types of spores; smaller microspores and larger megaspores.

The spores germinate to produce a haploid gametophyte, called prothallus. The homosporous pteridophytes produce bisexual gametophytes while heterosporous pteridophytes produce unisexual gametophytes.

In gametophytes, reproduction is of oogamous type. The male sex organs are called antheridia and female sex organs are called archegonia. Antheridia produce antherozoids and archegonia enclose the egg cell. Fertilisation requires water. The diploid zygote is retained in the archegonial venter where it develops into an embryo. Subsequently it becomes a young sporophyte and grows into an independent adult plant. Thus the life cycle includes an alternation of diploid sporophytic generation with a haploid gametophytic generation. Sporophytic generation is dominant in the life cycle.

fig. 8.30 - Life Cycle of Fern (A Pteridophyte)

Classification

Pteridophytes have been divided into three classes namely Lycopodophyta (club mosses), Sphenophyta (horse tails) and Filicinophyta (ferns).

 

 

fig. 8.31 - Examples of Pteridophytes

Lycopodophyta	Sphenophyta	Filicinlophyta
Leaves relatively small (microphyllous), spirally arranged around the stem	Leaves relatively small, arranged in whorls around the stem	Leaves relatively large (macrophyllous) and are called fronds, spirally arranged around the stem
Includes both homosporous and heterosporous forms	Includes only homosporous forms	Includes mostly homosporous forms
Sporangia mostly found in clusters (strobil or cones)	Sporangia in strobili, on sporangiophores	Sporangia usually in sori
Examples selegina(Homosporous)Lycoporous (heterosporous)	Examples Equisetum (Only surviving genus)	Example Dryoptera ‘pteridium