MARSILEA

Marsilea
• Occurrence
Marsilea is an aquatic or semi aquatic
plant. It is common in the temperate
regions. It grows in fresh water ponds
and ditches in
Punjab. Marsilea quadrifolia and Muni
lea minuta are commonly found in
Pakistan.

General structure
• The vegetative plant is a sporophyte. It is differentiated into roots, rhizome and
leaves.
• 1. Rhizome: The stem is in the form of a rhizome. Rhizome has unlimited
growth. Therefore, it covers a very large area. The rhizome is dichotomously
branched. It has nodes and internodes. A number of adventitious roots arise at
each node on the ventral side. But a single leaf arises at each node from the
dorsal side.
• 2. Leaves: The leaves are compound. Each leaf has a long petiole and four
:carats. The kallets are arranged in cross-like manner at the tip of the petiole.
Each leaflet is triangular. Veins form reticulate arrangement Stomata arc
located on the dorsal side and ventral side of the leaflets.

Internal Structure of the Rhizome
Internally the rhizome is composed of epidermis, cortex and central
stele.
1. Epidermis: It forms outer covering.
2. Cortex: The cortex is wide. Its peripheral part consists of
parenchymatous cells. Ring of a large air chambers are present
around this peripheral portion. This portion is called aerenchyma. It
stores air. The inner portion of the cortex is composed
Sclerenchymatous cells. Endodermis is present inner side of the
cortex.
3. The stele in Marsilea is of amphiphloic solenostele. It has pith in
the centre. Protoxylem groups are exarch in position.

Internal structure of leaf
Both surfaces of the leaf are bound by epidermis. Epidermis is
covered by cuticle. It has sunken stomata. Mesophyll cells are present
between both epidermises. Mesophyll cells are differentiated into
palisade and spongy cells. Single vein passes through each leaf.

Reproduction
Sporocarp
Marsilea plant is heterosporous. The megaspores and microspores are produced
in megasporangia and microsporangia. Both types of sporangia are found within
the same sorus. The sari are produced in hard fruit-bodies called sporocarps.
The sporocarps are attached to the base of petioles by short stalks (peduncles).
Sporocarp is bean shaped. It has hard and stony wall (capsule).

Its wall has single vascular bundle.
The sporocarp has two inner chambers. Each chamber has a row of sori. The
sori of two rows alternate with each other. The wall of each sorus is formed by
its own indusium. Each sorus contains a row of megasporangia and several
microsporangia.

A large placenta is produced on the inner side of the wall in the young
sporocarp. The placenta of two sides alternate with each other.
Megasporangia and microsporangia are produced on the same placenta.
Each placenta is covered by its own individual indusium. Megasporangia
mature earlier than the microsporangia. Each megasporangium contains a
single megaspore on maturity. But each microsporangium contains
several (32-64) microspores. All the tissues except indusia gelatinized in
mature sporocarp.

Development of the Sporocarp
It is believed that the sporocarp is a single folded pinna. This pinna has single vascular
bundle. Receptacles or placentas are produced on the ventral side of this pinna. These
receptacles bear sporangial initials. Each receptacle with the developing sporangia forms a
An outgrowth is produced towards the midrib side of pinna. outgrowth forms a covering over
the sorus. This covering is known as the indusium.

1 he pima becomes folded towards the ventral side due to the growth of
the tissue in the mid dorsal region. The two sides of the pinna meet at the
margin. It completely encloses the developing son. The hardening of cells
in the wall gives rise to the bean shaped sporocarp.

Dehiscence of sporocarp: The mature sporocarps open after two or three years.
The stony wall decay and open the sporocarp. The inner gelatinous material
absorbs water and swells. It splits the sporocarp into two valves. The gelatinous
cord or sporophore absorbs water and swells.
The spores remain viable for a very long period.

Development of the Sporangium
1. The sporangial initial cuts off a jacket initial to the outside. It itself becomes the
archesporial initial.
2. The jacket initial divides to produce single layered wall of the sporangium. The
archesporial initial cuts off two tapetal cells. These tapetal cells divide to produce two layered
tapetum. Tapetum is present inner to the wall.
3. The archesporial initial then divides producing 12-16 spore mother cells. Each spore mother
cell undergoes meiosis and produces four spores. The development of megasporangia and
microsporangia is similar upto the stage. Both sporangia contain 32 or 64 young spores
enclosed in a single layered wall.

4. The tapetal cells provide nourishment to young spore. So they
disintegrate during the development of spores.
5. In the megasporangium only one spore develops further. All others
disintegiate forming a mucilaginous mass or plasmodium. This mass
provides nourishment to the developing megaspore. In the
microsporangium all the spores develop into 32-64 microspores.

Development of the Male Gametophyte:
1. The microspore divides in to two cells. The smaller cell becomes prothalial
cell. It is reduced male gametophyte. The larger cell divides in two antheridial
initials.
2. Each antheridial initial divides to form three jacket cell and single
androgonial initial. The androgonial initial of each antheridium divides to
produces 16 androcytes (antherozoid mother cells). Each androcyte changes
into antherozoid.
3. The antherozoids have many coils and single flagella. The prothalial cell
and the jacket cells of both the antheridia disintegrate. Thus the antherozoids
become free in the Surrounding water.

Development of the Female Gametophyte
1. Megaspore divides in to two cells. A smaller cell occupies the whole beak.
The larger cell does not divide further.
2. This smaller cell functions as an apical cell. The apical cell divides and cut
off form single layered vegetative tissue. The apical cell then functions as an
archegonial initial.
3. This archegonial initial divides to produce a small primary cover cell at the
top and a central cell at the base.

4. The cover cell divides to form four neck initials. They divide to form a neck.
The central cell divides to produce a small upper primary canal cell and a lower
larger primary ventral cell.
5. The primary canal cell divides to produce two neck canal cells. The primary
ventral cell divides to produce a lower larger oosphere (egg) and an upper
smaller ventral canal cell.
6. The ventral canal cell and the neck canal cells of mature archegonium
disintegrate. It forms an opening for the entry of antherozoids

Fertilization
Each megaspore is enveloped by a layer of mucilage. Several antherozoids
enter into this mucilaginous. One of these antherozoids enters the
archegonium and fertilizes the egg to produce oosphere.
Development of the Sporophyte
The oospore divides to produces four cells. Two sister cells develop stem
and cotyledons. The other two cells develop into foot and root. The
vegetative cells of the gametophyte form a calyptra. It is two to three cells
in thickness. This calyptra forms envelop around the developing embryo.
The surface cells of the calyptra produce long rhizoids. Cotyledon and the
root grow faster than calyptra and conic out of it. The root enters the soil.
Cotyledon expands to form the first simple leaf. Primary root is replaced by
adventitious roots. 1 he stem grows horizontally on the soil and form the
rhizome.

Alternation of Generation
The sporophyte and gametophyte generations alternates with each
other. Vegetative plant of Marsilea is a diploid sporophyte. It is
hetrosporous. It produces mega and microsspores by meiosis. The
spore germinates to form haploid gametoplivte. The gametophyte
of Marsilea is dioecious. The microspores give rise to the male
gametophyte. The megaspore gives rise to the female
gametophyte. Both male and female gametophytes complete their
development within the spore walls. Both gametophytes produce
male and temale gametes. Gametes fuse to form diploid oospcire.
The oospore develops into the sporophyte again.