PTERIDOPHYTES
Pteridophytes are primitive seedless vascular plants also
called cryptogams. These have conspicuous sporophytic
plant body, inconspicuous independent gametophytes
with antheridia and partially embedded archegonia
having 4-rowed necks.
The term Pteridophyte was coined by Haeckel (1866).
About 13000 species of pteridophytes have been
reported. They were perhaps the first land plants evolved
during ordovician (450-500 million years ago) period.
The characteristic features of pteridophytes are as follows
Habitat
The pteridophytes are found in cool, damp shady places
though some may flourish well in sandy-soil conditions
Some members like Azolla, Salvinia, Marsilea species are
aquatic pteridophytes.
Plant Bodv
The size varies from a fraction of centimeter (e.g., Azolk}
to 20 m in tree ferns (e.g., Angropteris). The main plant
body is a sporophyte which is differentiated into
stem and leaves. These organs
root,
well-differentiated vascular tissues. The leaves are small
(microphyllus) as in Selagmella or large (macrophylls) as
in Dryopreris (ferns).
These plants evolved as first terrestrial plants to possess
xylem and phloem throughout their body. Xylem consists
of tracheids and phloem made up of sieve cells and
alburninous cells.
Sporoph.\lls
The sporophytes bear sporangia that are substended bv
leaf like appendages called sporophylls. In some cases
sporophylls may form distinct compact structure called
strobili or cones (Selagtnella and F.qmserum).
sporangia produce spores by meiosis in spore motha
The spores germinate to give rise to inconspicuous, sm
but multicellular, free-living, mostly photosynthdK
thalloid garnetophytes called prothallus. In maiori0′
the pteridophytes, all the spores are of similar kinds; su
dants are called homosporous.
Genera like Selaginella and Salvinia produce two kinds of
spores, macro (large) and micro (small) spores; thus, are
called heterosporous.
Ganwtophyte
The thalloid gametophyte or prothallus requires cool,
damp, shady places to grow. The megaspores and
nucrospores germinate and give rise to female and male
gametophytes, respectively. The female gametophyte in
these plants is retained on the parent sporophytes for viable
periods. In most ferns, prothallus is green and autotrophic.
In heterosporous ferns, the female gametophyte depends on
food stored by the megaspore.
The gametophytes bear male sex organs called antheridia
and female sex organs called archegonia. Antheridium is
sessile and surrounded by a single layered jacket.
Archegonium is flask-shaped. It is partially embedded.
Water is required for transfer of antherozoids (male
gametes). These are released from the antheridia and reach
to the mouth of archegonium through a film of water only.
Fusion of male gamete with the egg present in the
archegonium results in the formation of zygote. Zygote
develops into multicellular, well-différentiated sporophyte(2n)
which is the dominant phase of the pteridophytes.
Embryo
Fertilisation produces a zygote that undergoes division to
produce embryo. The development of the zygote into
young embryo rakes place within the female gametophyte.
•rhis event is a precursor of the seed habit and considered as
an important step in evolution, e.g., [)rvoprerts, Selaginella.
Adiantum. Equisetum and Salvima.
(i) Pteridophytes are a good sourcc of food for animals.
For cxatnple, sporocarps of Marsilea is edible.
Angtoprerts and have starchy pith eaten by
natives of Australia.
(ii) Ferns protect soil erosion by providing a good
cover on thc hill slopes and other fragilc places.
(iii) stctns tough surtaecs. They are used
In scrubbing and polishing.
(iv) a water tern has a association with
Anabaena azollae. It
IS cultured in paddy ticlds to harbour nitrogen-fixing
b.Rtcraum. ‘l -hus. It IS used as a biofertiliser.
(v) Rhizomes and pcuolcs of l)nopteris are used to
produce anti-hclnuntac drug. Roots of Adiantum can
cure throat Lycopodium is used in treatment
of rheumatism and disorders of lungs and kidneys.
(vi) Ferns are also grown as ornamental plants for their
graceful plant bodv.
‘Ehe pteridophvtes are further classified into four classes
(i) Pulopslda (
(ii) lxcopslda (.SeL.x:nella and Lycopodium)
(iii) Sphenop\lda (Equisetum)
(IV) Pteropsida (Drvopteris, Pteris and Adiantum)