II BSc IVth SEMESTER

1. MARSILEA

2. SYSTEMATIC POSITION
Division Filicophyta
Class Leptosporangiopsida
Order Marsileales
Family Marsileaceae
Genus Marsilea.

4. Characteristic features
 This order includes a single family, Marsileaceae.
 The family includes the living genera- Marsilea, Pilularia
and Regnellidium.
 They are heterosporous aquatic ferns.
 The sporangia of these are produced within special
structures known as sporocarps.
 Each sporocarp possesses many sori which bear
microsporangia and megasporangia.
 The sori are gradate, i.e., the oldest sori are found at their
terminal end of the receptacle and youngest at the base.

5.  There are about 65 species of Marsilea
distributed all over the world.
 They are more commonly found in tropical
regions, such as, Africa and Australia.
 They are hydrophytic or amphibious plants.
 They grow rooted in the mud of marshes and
shallow pools.
 A single plant of M. vestita may grow in all
directions until it covers an area twenty-five
metres or more in diameter.

6.  In M. vestita and most of other species the
sporocarps develop to maturity only on the plants
that are not submerged.
 M. minuta and some other species produce
sporocarps in the aquatic habitat; on the other hand
M. aegyptiaca never produces the sporocarps in the
aquatic habitat.
 An Australian species M. hirsuta can survive in dry
conditions throughout the year.

7. External Morphology:
Stem:
 The species of Marsilea possess a rhizome which creeps on or just
beneath the surface of the soil.
 The rhizome is slender, branched and possesses nodes and
internodes.
 The leaves are borne alternately along the upper side of the rhizome
usually at the nodes.
 One or more adventitious roots come out from each node on the
underside of the rhizome.
 The rhizome is dichotomously branched and is capable of indefinite
growth in all directions and covers an area more than twenty-five
metres in diameter.

8. Leaves:
 The leaves are borne alternately along the upper side of the
rhizome at the nodes.
 The leaves possess circinate vernation typical of most
Filicales (ferns). The young parts of the leaves of M. minuta
and others are covered with numerous multicellular hairs.
 The leaves of submerged plants possess long flexible
petioles and leaf lamina that float on the water surface.
 When the plants grow on mud or marshy places the leaves
have got shorter and the petioles erect and stouter which
spread the leaves in the air.

9.  The veins of each pinna are dichotomously
branched and have numerous cross connections
resulting in close reticulum of veins.
 The shape of pinnae varies from obovate to
obcuneate. The margin also varies from entire to
crenate, e.g., M. minuta or from crenate to lobed
as in M. aegyptiaca a xerophytic form.
 At night the pinnae of aerial leaves become folded
upwards and exhibit the sleeping movement.

10.  The sporocarps are borne on short peduncles near the
base of the petiole.
 In majority of cases the peduncle or stalk of the
sporocarp is unbranched and bears a single
sporocarp at its apex.
 Marsilea quadrifolia possesses dichotomously
branched peduncle, which bears two to five
sporocarps.
 In M. polycarpa single dichotomously branched
peduncle bears about 6 to 26 sporocarps.

11. Roots
 One or more adventitious roots are borne at each
node on the underside of the rhizome.
 The adventitious roots may arise even from
internodes, e.g., in M. aegyptiaca.
 In M. minuta the roots may develop laterally.
 The roots of M. minuta secrete carbonic acid and
because of this secretion the roots could penetrate
the shells of pond snails.

12. Anatomy
Rhizome
 The rhizome of Marselia possesses an amphiphloic siphonostelic
vascular cylinder.
 The outermost layer is the single- layered epidermis without any
stomata.
 The cortex is differentiated into outer and inner cortical regions. The
outer cortical region consists of compact parenchymatous tissue.
 This region may be one to several celled in thickness. Just beneath
this the cortical region contains large lacunae or air spaces
(aerenchyma).
 The lacunae are separated from each other by one layered
parenchymatous septa.

13.  This region may be considered the middle cortex.
 Internal to this region the inner cortex is found.
 This consists of a sclerotic zone. The cells consisting
this region are thick-walled sclerenchymatous cells
(fibres).
 Beneath this region the cortex again consists of
compact parenchymatous tissue acting as storage
tissue containing starch in them. Some of the tannin
cells may be found in this innermost region.

15. Petiole
 The internal structure of a petiole transverse
section is as follows-
 The outermost layer is single-layered epidermis.
 Just beneath the epidermis there is hypodermal
layer.
 Then there is other cortex constituting of large air
spaces or lacunae (aerenchyma) separated from
each other by septa.

16.  The inner cortex is composed of compact
parenchymatous cells.
 In this region some of the tannin cells may be present here
and there. In the central region of the petiole there is stele
which is more or less triangular in outline.
 The stele is surrounded by a single- layered endodermis.
 It possesses V-shaped mass of xylem with the exarch
protoxylem.
 The two arms of V are quite separate and somewhat
curved from each other.

18. Root
 In the transverse section of the root, the epidermis,
cortex and stele may be seen.
 The epidermis is single layered and composed of thin-
walled parenchymatous cells.
 The cortex of the root is differentiated into two
regions.
 The outer region consists of large air spaces or
lacunae separated by septa from each other the inner
zone of the cortex consists of a few layers of sclerotic
cells.

19.  Inner to the cortex there is single layered
endodermis.
 Just beneath the endodermis there is single-
layered pericycle.
 In the centre of the stele there is typical
diarch and exarch structure with a diametric
plate like strand of xylem.
 The phloem bands are found on either side of
the xylem plate.

21. Reproduction:
The reproduction in Marsilea takes place by vegetative and
sexual methods.
Vegetative propagation
 The vegetative reproduction takes place by means of
specially developed structures known as tubers.
 In the dry conditions certain branches develop from the
rhizome, which swell because of the storage of food
material, and are termed as tubers.
 These tubers survive in the unfavourable and drought
conditions, and on the return of favourable conditions they
germinate into new plants, e.g., M. hirsuta.

22. Sexual reproduction
 The plant is a sporophyte.
 It bears the special structures known as sporocarps
which contain micro and megasporangia in them.
 It is heterosporous. The sporocarps are borne on short
peduncles above the base of the petiole.
 In most cases the peduncle is unbranched and bears a
single sporocarp at its apex.
 In M. quadrifolia the peduncle is dichotomously
branched and bears 2 to 5 sporocarps.

25.  The sporocarps may be oval or bean-shaped.
 In the earlier stages of its development it is
soft and green but later on it becomes
sufficiently hard and brown in colour.
 Such protuberances consist of one or two
teeth and raphe.

26.  The raphe is found laterally fused to base of
the sporocarp at the end of the peduncle.
 Beyond the raphe two teeth or projections are
found. These teeth are unequal in size.
 The lower tooth is stouter than the upper one.
In some species the teeth are very prominent.

27.  A receptacle develops at the region where
each lateral vein forks dichotomously.
 The receptacles of one valve alternate with
those on the opposite valve of the sporocarp.
 A flap-like outgrowth two-celled thick extends
like a hood over the entire receptacle.
 Each receptacle projects inward from the wall
of the sporocarp.

28. Life Cycle of Marsilea:
 Mature plant of Marsilea is diploid.
 Marsilea is a heterosporous fern because it produces 2
different types of spores i. e., microspores and
megaspores.
 Micro- and megaspore mother cells are produced inside
micro- and megasporangium respectively which represents
the late stage of sporophytic generation.
 After reduction division microspores and megaspores are
produced which represent the initial stage of gametophytic
generation.

29.  Microspore gives rise to male gametophyte which, in
turn, produces archegonium and egg.
 Both antherozoid and egg fuse to from a diploid
oospore (2x).
 The oospore is the initial states of sporophytic
generation. Hence, in the way the sporpytic and
gametophytic generation alternate with each other
although the sporophytic phase is dominant over
gametophytic phase