Marsilea is a genus of approximately 65 species of aquatic ferns of the family Marsileaceae. (1).pdf

Marsilea

1. marsilea

2. DIVISON
CLASS
ORDER
FAMILY

PTEROPHYTA
LEPTOSPORANGIOPSIDA
MARSILEALES
MARSILEACEAE

CLASSIFICATION

3. Marsilea is worldwide in distribution. it is rich in warmer parts of the world such
as tropical Africa and Australia. It is well represented in northern hemisphere.
About 9 living species have been recorded from India. Of these M. minuta is
commonest. It is practically found all over India.
M. brachypus, M. quadrifolia, M. rajasthanensis and M. aegyptiaca are
theother important Indain species.
DISTRIBUTION

4. Commonly called as water fern.
Aquatic or amphibious, sometimes xerophytic
pteridophyte.
All the species are rooted either in mud or soil.
Indian species: M. minuta, M. quadrifolia,
M. rajasthanensis
HABITAT

5. MORPHOLOGY
Plant body is a sporophyte.
Differentiated into three parts:
-Stem
-Roots
-Leaves

6. STEM

Long and slender
It creeps either on the surface like a stolon or slightly along the
surface of the soil like rhizome.
They are dichotomously branched, branches arise from axils of
leaf.
Stem is divisible into distinct nodes and internodes.
Roots and leaves arise from the nodes.

7. Leaves arise from the upper side of the stem alternately and are
arranged in two rows.
The lamina consists of 4 leaflets (pinnae) which are present at the
apex of the petiole.
The 4 leaflets arise as a result of 3 dichotomies of the lamina in a
close succession to each other.
2 leaflets arise slightly higher than the 2.
The leaf apparently looks quadrifoliate. Actually it is quadrijugate.
It looks like a four-leaved clover plant.
leaves

8. Leaflets are obovate, elliptical with entire or serrate margins.
Petiolate and compound.
(submerged plants- long, thin and flexible with the lamina floating on the
surface of water.
Mud/land plant- petiole is upright, short with the lamina held in a spreading
position)
Leaflets are obovate, elliptical with entire or serrate margins.
They shows Circinate vernation.
Reticulate venation. Veins divide repeatedly in a dichotomous manner.
At the base of the petiole are found the spore bearing organs, the sporocarps.
Leaves exhibit sleeping movements.

9. ROOTS

Primary roots are short-lived which are replaced by one or more
adventitious roots from the underside of the nodes the rhizome.
Sometimes they may arise from the internodal region.
They are thin, and may be branched or unbranched.
Branching is monopodial.

10. ANATOMY
-Stem
-petiole
-Leaflet
-Roots

11. stem

Epidermis
Cortex
Stele
The anatomical section of stem is circular in outline and reveals the
following structures;
1.
2.
3.

14. Epidermis forms the outermost and continuous single layer of cells,
uniseriate, without stomata.
They are thick walled and compactly arranged.
Epidermis
Cortex is differentiated into 3 regions.
-Outer cortex
-Middle cortex
-Inner cortex
Cortex

15. Outer cortex
It consists of compactly arranged parenchymatous cells.
Here and there among them occurs few tannin cells.
They serves to maintain the cylindrical form of stem.
Middle cortex
It consists mainly of air cavities.
Aerenchyma- air storage tissues consisting of single layer of air
chambers arranged in a ring.
Trabeculae- The chambers are separated from one another by
single layered partitions consisting of thin-walled parenchymatous
cells.

16. Inner cortex
They are solid tissue of several cells in thickness
They can be divided into two layers ; inner and outer cell layer of
inner cortex.
Outer cell layers are thick-walled or sclerotic constituting the
sclerenchyma
Inner layer of cells of inner cortex are compactly arranged
parenchymatous and some of these cells may contain tannin while
others are filled with strach.

17. The vascular cylinder is medullated.
Amphiphloic siphonostele -
The xylem is in the form of a ring and there is phloem on both sides of
the xylem.
Both the inner and outer phloem are covered by pericycle which is
single layered.
The pericycle in turn is flanked by endodermis.
The medulla or pith which is delimited by inner endodermis, occupies
the Centre (it is parenchymatous in plant growing in water and
sclerotic in plant growing in mud or damp soil.)
Stele

18. In a section passing through or near the node, the vascular cylinder
consists of two parts, an arc-like or c-shaped stele and a leaf trace. The
inner and outer layers of endodermis, pericycle, and phloem become
continuous at the end of the arc-like stele.

19. Stele
The various disposition of various
tissues from outwards to inwards;-
Outer endodermis, outer pericycle,
outer phloem, xylem (diarch), inner
phloem, inner pericycle, inner
endodermis and pith.

20. PETIOLE

Epidermis
Cortex
Stele
The anatomical section of petiole reveals the following structures;
1.
2.
3.

22. Epidermis
Epidermis is the outermost and single layered made up of rectangular cells.
Cuticle is present.
Cortex
Cortex is differentiated into three regions;
-Outer cortex
-Middle cortex
-Inner cortex

23. Stele
The stele is somewhat triangular in outline and consists of a single vascular
bundle.
Xylem (exarch) part of the bundle is shaped like the letter 'V' with the opening
towards the axis.
The arm has sometimes more large tracheids in the middle with a few smaller
ones at either ends.
Xylem parenchyma is present in between the two arms of the xylem.
Surrounding the xylem is the phloem followed by the pericycle.
The pericycle is bounded by the endodermis.

26. LEAFLET

Epidermis
Mesophyll
Stele
The anatomical section of leaflet shows following regions;;
1.
2.
3.

30. Epidermis
There are two epidermis; lower and upper epidermis.
They are made up of parenchymatous cells, uniseriate.
Their continuity is interrupted by slightly sunken stomata.
( epidermal cells have more wavy walls in plants growing under drier habitats
than those found in water.)
( the stomata are restricted to the upper epidermis only in the hydrophytic sp.
and are present in both epidermis in terrestrial plants.)

31. Mesophyll
It occupies a wide space between between upper and lower epidermis.
It is usually differentiated into upper palisade tissue and lower spongy
parenchyma.
Palisade tissue- it is made up of elongated cells provided with chloroplast.
Spongy tissue- they are made up of loosely arranged parenchymatous cells
with large air chambers separated by single layered septa.
In submerged species, the mesophyll is not differentiated into palisade and
spongy tissues.

32. Stele
In between the mesophyll tissue are present several vascular bundles.
Each vascular bundles are concentric and amphicribal type i. e., made of a
centrally situated xylem, surrounded on all sides by phloem.
The bundle is enclosed by a single layered thick endodermis.

33. ROOT

The anatomical section of root gives three main regions.
Epidermis
Cortex
Stele
1.
2.
3.

36. Epidermis
It is the outermost single layer made up of parenchymatous cells.
Cortex
It can be differentiated into three parts;
-Outer cortex
-Middle cortex
-Inner cortex

37. Outer cortex- the outer cortex is aerenchymatous (consists of a large air
chambers arranged in the form of a ring. These chambers are separated from
each other by a longitudinal septa made up of parenchymatous cells.
Middle cortex- the middle cortex is compact parenchymatous cells.
Inner cortex - the inner region is sclerenchymatous cells.
- it is delimited by single layered thick endodermis.

38. Stele
It is of protostelic type and occupies the central position within the endodermis.
It is devoid of pith.
Plate like xylem is situated in the centre which is diarch and exarch.
In the middle of the elongated xylem plate are two large and small metaxylem
elements.
The protoxylem is exarch. It consists of two small masses of still smaller protoxylem
cells one at each end and touching the pericycle.
On either side of the xylem plate is the band-like phloem.
The phloem is bounded externally by a single layer of pericycle.

40. REPRODUCTION

41. tuber

Vegetatively Marsilea plants reproduce by the formation of tubers.
During dry periods, certain branches develop from the rhizome.
They are small, bud-like structures.
Each tuber contains reserve food material in the central portion and is covered
with minute reduced scale leaves.
It serves as perennating organ, sprouting with the return of conditions favorable
for growth.
Tuber formation has been reported in M. minuta and M. hirsuta.

42. sporocarp

44. sporocarp

The sporocarps are special fruiting bodies ( reproductive bodies) of Marsilea.
The micro and mega-sporangia are borne in special bean-shaped sporocarps.
They are bisporangiate.
They are oval or bean shaped ( M. minuta and other hydrophytic species) or
squarish or rectangular ( M. aegyptiaca or other xerophytic species).
When young, the sporocarps are soft, green and covered with hairs and
become brown-dark brown, hard and nut-like at maturity.
They are borne on short or long stalks called peduncles or pedicels which are
attached to the petiole.

45. Three distinct types of attachment of the pedicels to the petiole are found in the genus;
a) Pedicels directly inserted on the petiole in a linear sequence on the same side.
( M. polycarpa and M. subangulata )
b) Pedicels connate among themselves and jointly attached to the petiole.
(M. quadrifolia )
c) Pedicels free or slightly connate and attached to the base of the petiole by a single point.
(M. minuta )
The portion where the sporocarp attaches with the pedicel is called the raphe.
Above raphe the sporocarp has one or two horn shaped protuberances called tubercles.
They are also known as teeth or horn. ( not every species has this tubercles)

47. internal structure of the sporocarp

The bivalved sporocarp has a thick and resistant wall.
A mature sporocarp has a 3 layered wall;
a) Wall of the sporocarp
-Outermost layer : epidermis
- Middle hypodermis
- Inner parenchymatous zone

48. sunken stomata

epidermis

palisade layer

parenchyma

51. Outer epidermis
It is a single layered made up of broad and columnar cells.
Its continuity is broken by the presence of sunken stomata.
Some of the epidermal cells develop into multicellular hairs.
Middle hypodermis
There are two layers of outer and inner elongated palisade like cells.
Both the layers have chloroplast in their cells.
Outer layer- cells are thick walled and continuous all around the sporocarp.
Inner layer - cells are thin-walled and more elongated and it is not a continuous layer
around the sporocarp.

52. Inner parenchymatous zone
Inside the second palisade layer is present a two or more cells thick
parenchymatous region.
The cells are uninucleate and vacuolated.
The cells of this region near raphe gelatinise in a mature sporocarp which helps
in the dehiscence of the sporocarp.
The inner parenchymatous cells form gelatinous tissue called the sporophore
that runs around the sporocarp cavity, in a dorsiventral plane.

53. The sori are elongated and arranged in two alternating rows in the cavity of the
sporocarp, each row lies in the cavity of the valve and is situated dorsiventrally and
transversally to the long axis of the sporocarp.
Each sorus arises on a ridge-like placenta or the receptacle that is borne on the
sporocarp wall and is covered by membranous indusium made up of two layers of cells.
The sori overlap each other and the indusia of adjacent sori are partially fused.
The number of sori in a sporocarp varies from two ( M. aegyptiaca ) to twenty
( M. quadrifolia, M. vestita ).
Each sorus bears both mega and microsporangia. The former are short-stalked and are
arranged in a row at the tip of the receptacle, whereas the latter are long stalked and
arise on the sides.
b) The sori

54. HORIZONTAL LONGITUDINAL SECTION (HLS)
In HLS, the gelatinous ring appears in the form of a dorsal and ventral mass.
Dorsal mass is more prominent than ventral mass.
Microsporangia and Megasporangia are found are found in two alternate rows.
Each sorus has a receptacle which contains a terminal megasporangium and two
lateral microsporangia .
Each sporangium is surrounded by an indusium.

57. VERTICAL TRANSVERSE SECTION
Gelatinous ring appears as a dorsal mass and a ventral mass
In a particular plane, the sorus can be seen only with microsporangia or
megasporangia
Lateral bundle extending from dorsal to ventral side and placental bundle
arising from lateral bundle can be seen

59. VERTICAL LONGITUDINAL SECTION
Gelatinous ring appears as a complete ring around the sori which are arranged in
many vertical rows
Either micro or megasporangia are seen
If section is exactly median, only megasporangia are visible, if it is slightly away from
median line, only microsporangia are seen

63. VASCULAR SYSTEM OF SPOROCARP
Receives vascular supply from petiole
Single strand enters the stalk, extends through raphe and passes along dorsal side-
dorsal bundle
Traces are given out on both faces of the sporocarp and extends downwards called
lateral bundles or commissural bundles
Each lateral bundle is dichotomously branched
Adjacent bundles anastomose and form loops
From the point of dichotomy a small branch called placental bundle enters the
sporangia bearing receptacle

64. development of sporangium


Sporangial development is of the leptosporangiate type. The development of both the micro-
and megasporangia is almost alike. The sporangial initials for megasporangium and
microsporangium are formed at top and at the sides of the receptacle, respectively.
The initial cell divides periclinally (transversely) into an outer and an inner cell. The inner cell
does not take part in further development. The outer cell undergoes three successive diagonal
divisions and forms a tetrahedral apical cell with three cutting faces.
This apical cell cuts off two seg­ments along each of its three cutting faces which forms the stalk
of the sporangium. Now the api­cal cell divides with the help of an arched peri­clinal wall towards
its outer face and forms an outer jacket initial and an inner tetrahedral archesporial cell. The
outer jacket initial divides anticlinally to form a single-layered jacket.

66. The archesporial cell divides periclinally to forms an outer tapetal initial and an inner primary
sporogenous cell. Anticlinal and periclinal divi­sions of the tapetal initial forms a two-layered
thick tapetum.
The primary sporogenous cell divides to form a mass of either 8 or 16 spore mother cells. Spore
mother cells (2n) undergo meiotic division to form 32 or 64 haploid spores (n). The developments
of both the sporangia are similar up to this stage.
In megasporangium, only one megaspore survives to become a large functional megaspore,
while all the microspores are functional in microsporangium.

67. A sporocarp is a hard structure and it does not open until two or three years after their
formation. This delay is probably due to the imperviousness of the hard sporocarp wall.
The sporocarp may remain viable for even 50 years. The tissues slowly swell up by
absorbing water in natural conditions. Thus the swelling puts pressure on the wall of the
sporocarp and eventually it splits open along its ventral side into two halves.
Splitting is followed by the emergence of a long, worm-like gelatinous structure to which the
sori are attached
The mucilaginous cord may become ten or fifteen times larger than the sporocarp.
Following the release of the sori from the sporo­carp, the indusia and the sporangial wall
disinte­grate and the spores are liberated.
dehiscence of sporocarp

69. development of gametophyte

Gametophyte:
Marsilea is heterosporous i.e., they produce microspores and megaspores which
eventually germinate to form the male and female gameto­phytes, respectively.
The microspores are small, globose struc­tures with a thick outer ornamented exine
and inner thin intine. The outer exine is covered by a thin layer called perispore.
The microspore con­tains a distinct haploid nucleus and its cytoplasm is rich in
starch grains.
Male Gametophyte:

70. The microspores germinate inside the spore wall (endosporic type) almost
immediately after its release . It divides asymmetri­cally to form a small prothallial
cell and a large apical cell . A division of apical cell diagonal to prothallial cell
forms two antheridial cells.
Then both the antheridial cells divide diag­onally with curving wall forming the
first jacket cell and large wedge-shaped cell. The jacket cells do not divide, but
the wedge-shaped cell divides periclinally to form smaller inner cell (2nd jacket)
and a large outer cell. Further, the periclinal division of outer cell forms 3rd
jacket and primary androgonial cell.

71. At this stage the male gametophyte consists of one prothallial cell, 6 jacket cells and 2
androgonial cells. After several divisions of the primary androgonial cells, sixteen androcytes
are formed surrounded by jacket cells.
Later the prothalial cell and the jacket cells disintegrate and the two groups of androcytes,
representing the two antheridia, float freely in the cytoplasmic mass within the original spore
wall. Each androcyte becomes a motile antherozoid by dissolution of the androcyte
membrane.
The antherozoids are corkscrew-shaped, multiflagellate structure cha­racterised by the
presence of a large posterior cytoplasmic vesicle

73. The megaspore is an oval or elliptic structure, the wall of which imbibes water and expands
to form a gelatinous mass around the megaspore. The spore wall expands to form a small
papilla (protuberance) at the apical end where the nucle­us is located in a dense part of
cytoplasm. The remaining portion of the spore is filled with a frothy cytoplasm full of starch
grains
The first division in the apical nucleus of the large megaspore is transverse, forming a
small nipple-shaped apical cell and a very large basal nutritive or prothallial cell .The
prothallial cell provides the nutrition to the grow­ing female gametophyte.

Female Gametophyte:

74. A small neck (2 tiers of 4 cells each) is derived from the primary cover cell. The central cell
divides transversely to form an upper primary canal cell (behaves as neck canal cell) and
lower primary venter cell
The primary ventral cell again divides transverse­ly to form a ventral canal cell and an egg.
The growth of the archegonial complex ruptures the megaspore wall at the apical end and
forms a conspicuous gelatinous mass with funnel-shaped papilla or protuberance. Now, the
megaspore splits through the triradiate fissure and archego­nium becomes exposed.
The apical cell further divides by three intersecting vertical walls to establish an axial cell
surrounded by three late­ral cells .Now the axial cell func­tions as archegonial initial which
divides pericli­nally to form an outer primary cover cell and an inner central cell.

76. The free swimming antherozoids are attracted chemotactically towards the neck of a
mature archegonium but only one enters the neck and reaches the egg.
The male and female nuclei fuse to form a diploid structure called oospore or zygote.
Thus the gametophytic generation ends and the unit of sporophytic generation is
formed.
Fertilization

77. Oospore is the initial stage of sporophytic generation. The first division of the oospore is in a
vertical plane (parallel to the long axis of archegonium) to form 2 unequal cells. The bigger
one is known as epibasal cell and the smaller one as hypobasal cell . This is followed by a
second transverse division to form 4 cells (quadrant stage) .

Development of embryo

78. The epibasal half gives rise to shoot and leaf whereas the hypobasal half gives rise to root
and foot. The cell of epibasal half near the neck gives rise to cotyledon and other away from
the neck, to the stem.
In the same way the cell of the hypobasal half near the neck gives rise to root and other
away from the neck, to the foot. Simultaneously, the tissue surrounding the archegonium
divides to form a 2 or 3 celled thick calyptra which protects the embryo in young stage. The
embryo later on gives rise to an adult plant.

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