Pteropsida

PTEROPSIDA
BY:-
RANA ARSALAN JAVAID
PMAS ARID AGRICULTURE
UNIVERSITY RAWALPINDI


PTEROPSIDA
A large group of vascular plants characterized by
having parenchymatous leaf gaps in the stele and by
having leaves which are thought to have originated
in the distant past as branched stem systems.
Some botanists regard the Pteropsida as a natural
group which they recognize as a class, subdivision,
or division. Others regard it as an artificial
assemblage of plants that have undergone certain
similar changes from a rhyniophyte ancestry.
The various components of the Pteropsida are here
treated as three separate divisions under the names
Magnoliophyta, Pinophyta, and Polypodiophyta.

GENERAL CHARACTERISTICS OF
PTEROPSIDA
 Occurrence:
 Most pteridophytes are terrestrial and grow in moist
and shady places while some flourish well in open,
dry places especially in xeric conditions. Some
pteridophytes are aquatic and some are epiphytes.
 The sporophyte is the conspicuous and familiar plant
body. It develops from the zygote, a diploid cell
which results from the fertilization of the egg and
antherozoid.
 The sporophytic plant body remains differentiated
into true roots, stem and leaves. Some primitive
members lack true roots and well developed leaves
(e.g., in Psilophytales and Psilotales)

 Reproduction:
 The sporophytes reproduce by spores which are
produced within sporangia.
 In some pteridophytes the sporangia develop on
stems (i.e., cauline in origin) while in other they are
borne either on the leaves (foliar) or in the axils of
the leaves. The leaves that bear sporangia are
known as sporophylls.
 The sporophylls may be widely scattered on a
plant (e.g., ferns) or may be clustered in definite
areas and structures called cones or strobili
(Selaginella, Equisetum).

 The gametophyte:
 The spores on germination give rise to the haploid
gametophytes or prothalli which are small and
inconspicuous.
 The gametophytes in some pteridophytes are
subterranean and in others they are retained within
the resistant wall of the spore.
 The antheridia:
 The antheridia may be embedded in the
gametophyte or they may project from it.
 The embedded antheridia are commonly found in
eusporangiate pteridophytes while the projecting
ones are usually found in the leptosporangiate ferns.

 The archegonia:
 The archegonia are flask-shaped. Each archegonium
consists of a basal swollen, embedded portion the
venter and a short neck. The venter encloses the egg
and ventral canal cell.
 At maturity the apical cells of archegonium separate,
the neck canal cells disintegrate forming a passage
for antherozoids to reach the egg.
 Fertilization:
 In all cases the fertilization is accomplished by the
agency of water. With the result of the fusion of male
gamete and female egg a diploid zygote (2n) is
formed.

 The embryo (The young sporophyte):
 The zygote undergoes repeated divisions to form a
new sporophyte.
 The young sporophyte remains attached to the
gametophyte by means of a foot and draws
nourishment from the prothallus until it develops its
own stem, roots and leaves.
 The sporophyte is dependent on the gametophyte
only during its early stages.

CLASSIFICATION OF PTEROPSIDA
Pteropsida is further subdivided into following categories:-
The characteristic features of these divisions are as follows-

 1. Lycophyta:
 The sporophyte is differentiated into stem, roots, and
leaves.
 The leaves are microphyllous, and with a single vein.
 The vascular strands or steles may be protostelic,
siphonostelic, or polystelic.
 The leaf-gaps are always absent; sporophylls
produce a single sporangium on the adaxial side near
its base.
 The sporophylls are borne in strobili.
 They are homosporous or heterosporous.
 The antherozoids are biflagellate or multiciliate.

2. Psilophyta:
 The sporophyte is differentiated into a rhizoid
bearing subterranean rhizome and an aerial portion.
 The aerial portion is branched.
 The vascular system is of protostelic type.
 Leaf gaps are absent from vascular cylinder.
 The terminal sporangia are borne singly at the tips
of short or long branches.
 The gametophyte is subterranean and colourless.
 They are homosporous.
 Antherozoids are multiciliate.

3. Arthrophyta:
 The sporophyte is differentiated into stem, roots and
leaves. The stem possesses distinct ridges and
furrows.
 The foliage leaves are borne in transverse whorls
upon stems and their branches.
 The vascular cylinder is protostelic or siphonostelic.
The leaf-gaps are absent.
 The sporangia are produced upon a specialized
structure, the sporangiophores present at the apex of
the stem.
 The antherozoids are multiciliate.

4. Filicophyta:
 The sporophyte is differentiated into stem, leaves
and roots.
 With the exception of protostelic forms, the other
siphonostelic forms possess leaf-gaps in their
vascular cylinders.
 The leaves are macrophyllous.
 The leaf bears many sporangia on either the margin
or the abaxial face of the leaf lamina.
 The antherozoids are multiciliate.
 The sex organs are found on the ventral surface of
the heart-shaped prothallus (gametophyte).

 How did Pteridophytes Plants Originated?
 The pteridophytes occupy the intermediate position
in between the bryophytes on one hand and the
phanerogams on the other.
 They possess certain combinations of major
characters which are not found in bryophytes or in
phanerogams.
 The most characteristic feature of the pteridophytes
is the presence of independent gametophytes and
sporophytes at maturity.
 The pteridophytes are also known as ‘vascular
cryptogams’.
 The sporophytes of these plants possess a well
developed system of conduction tissue which
consists of xylem, phloem and other mechanical
elements.

 Origin Of Bryophytes from Pteridophytes:
 According to other school of thought the bryophytes
have been originated (descended) from
pteridophytes by means of reduction.
 This view could not get general support yet several
workers postulated the evidences in support of this
view.
 According to Lang (1917), Kidston and Lang (1917),
Scott (1923), Halle (1936), Haskell (1949) and
Christensen (1954) the bryophytes have been
descended by the process of reduction from
pteridophytes.
 Kashyap (1919) also supported the view, because of
common resemblances of the two groups.

 Similarities between sporangia of some members of
Psilophytales (Rhynia, Horneophyton and
Sporogonites) with capsules of Anthocerotales,
Sphagnum and Andreaea led to conclude this
hypothesis.
 The Psilophytales are the oldest pteridophytes in
which the sporophytes were rootless, leafless and
dichotomously branched with terminal sporangia.
 Such sporophytes resemble the bryophytes,
especially the members of Anthocerotales and are
thought to have evolved by progressive reduction.
--------------------------------------------------------------------------
THE END
--------------------------------------------------------------------------

Pteropsida

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (20)

Similar to Pteropsida

Similar to Pteropsida (20)

Recently uploaded

Recently uploaded (20)

Pteropsida