- The spores germinate to produce haploid gametophyte, called prothallus.
- The homosporous pteridophytes produce bisexual gametophytes (both antheridia and archegonia are borne on same prothallus)
whereas heterosporous ones produce unisexual (antheridia and archegonia develop on separate male and female prothallus)
gametophytes. - The sexual reproduction is oogamous.
- Antheridia are small and sessile male sex organs comprising
of androcytes each of which produces a male antherozoid.
Archegonia are female sex organs partially embedded and
consists of 4-rowed neck. - Water is essential for fertilisation, as it assists in
carrying bi-or multiflagellate sperms to archegonia. - The diploid zygote formed after fertilisation develops
into an embryo which remains attached to the
gametophyte and gets nourishment during its early
stage of development. - Pteridophytes exhibit alternate succession of sporophytic and
gametophytic generation. - Pteridophytes can be classified into following types:
Pteridophyta
Psilophyta- These are oldest known
land inhabiting plants. - Rootless, rhizoids
are present. - Homosporous
- Most plants are fossils, e.g.,
Rhynia, Horneophyton etc.
Lycophyta- Commonly called club
mosses or spike mosses. - Roots, stem and leaves
are present. - Members are microphyllous.
- Homosporous (Lycopodium) or
heterosporous (Selaginella).
Sphenophyta- At nodes, whorls of small
leaves are present. - Deposition of silica in stems
make them rough in touch. - Ridges and grooves are found in stem.
- Always homosporous,
e.g., Equisetum.
Pterophyta/Filicophyta- Fan like leaves.
- Stem is in the form
of rhizome. - May be homosporous
(Dryopteris, Pteris)
or heterosporous
(Marsilea).
Economic Importance of Pteridophytes
- Many ferns are grown as ornamental plants in gardens for their large, showy and graceful foliage.
- An anti-helminthic drug is obtained from the rhizomes and petioles of Dryopteris. Adiantum roots are used to cure throat
infections. Lycopodium is used in treatment of rheumatism and disorders of lungs and kidneys. - The sporocarps of Marsilea are rich source of starch and eaten for their nutritive value by some tribals.
Evolution of Seed Habit- The ability of plant to form seed is called seed habit. It is considered to be originated in pteridosperms during Devonian-
carboniferous periods. The development of zygote into young embryo within female gametophyte in heterosporous plants
e.g., Selaginella is a precursor to the evolution of seed habit. - The differentiation of spores into microspores and megaspores and their dependence on the parent sporophyte for the
nutrition are certain features considered as pre-requisites for the formation of seeds.
- Name the major pigments present in the following algae: Sargassum, Ulothrix, Porphyra.
- Bryophytes remain small sized and seldom attain great heights. Give reasons.
- Give an example of (a) homosporous pteridophyte (b) heterosporous pteridophyte.