Morphology of Marsilea Systematic position Kingdom : Plantae - CEC

Morphology of Marsilea 

Marsilea, commonly known as water fern, is represented by about 53 living 

and 10 fossil species. The living species occur in all parts of the world, but are 

more common in the warmer parts of the world, such as tropical Africa and 

Australia. They are aquatic or amphibious; the aquatic species usually grow in 

shallow ponds, but fruiting bodies (sporocarps) are formed only in the 

terrestrial habitats. The amphibious species grow in water-logged soil, partly 

submerged. Marsilea condensate and M. rajasthanensis are near xerophytic 

and M. hirsuta, an Australian species, can withstand long dry spells. In India, 

the genus is represented by 9 living species; of these M. minuta is the most 

widely distributed. It is practically found all over India. In Punjab, it is very 

common after the rains. M. brachypus, M. quadrifolia, M. rajasthanensis and 

M. aegyptiaca are the other important Indian species. Four species have been 

reported from Rajasthan. Species, such as M. minuta and M. quadrifolia 

are hydrophytic. They grow submerged or partially out of water. 

Systematic position 

Kingdom : Plantae 

Division : Pteridophyta 

Sub-division : Pteropsida 

Class : Filicophyta 

Order : Marsileales 

Family : Marsileaceae

Genus : Marsilea Linn. 

Common Name : Water Fern 

The plant body of Marsilea is sporophytic having diploid chromosome 

number in its somatic cells. During sexual reproduction, it produces male and 

female gametophytes, which are haploid in nature and form the sperm and 

egg, respectively. The sporophyte is differentiated into rhizome, roots, and 

leaves. 

Rhizome (Stem): The stem is a long and slender rhizome (Fig. 1). It creeps 

either on the surface like stolon, or slightly below the surface of the soil like 

rhizome. It grows extensively and is branched. The branches arise at the 

bases of petioles and are extra-axillary in position, arising in the lateral or 

oblique position. They run in all directions and may get rooted at the nodes. In 

this way, a single plant may cover an extensive area of about 20 metre’s 

diameter or even more. The stem is divisible into distinct nodes and 

internodes. The internodes are long in the hydrophytic species, and short in 

the sub-terrestrial or xerophytic species. 

Fig. 1 Creeping and slender rhizome of Marsilea sp.

Root: The primary root formed on the stem is short-lived and is soon replaced 

by adventitious roots, which arise gradually at the nodes on the underside of 

the stem (Fig. 1). Sometimes, roots may also arise at internodes (Marsilea 

aegyptiaca), or laterally (M. minuta). The roots are thin and may be branched 

or unbranched. They develop in an acropetal sequence, i.e. the youngest root 

is towards the apex of the rhizome. The number of roots at a node and their 

size vary considerably. 

Leaves: The leaves arise from the upper side of the stem and are arranged in 

two alternate rows (Fig. 1). They are long-petioled and compound. The 

petioles of the submerged plants are long, thin and flexible, with the lamina 

floating on the surface of water, while the leaves of plants growing in mud or 

on land have upright, short petioles, with lamina held in a spreading position. 

The lamina is usually divided into four leaflets of the same size. They spring 

from the tip of the petiole, so that the leaf apparently looks quadrifoliate. 

Occasionally, the number of leaflets may be 5 or 6, or even 8, instead of the 

usual 4. In outline the leaflets are obovate, elliptical, or wedge-shaped, with 

entire or dentate margins. 

According to Puri and Garg (1953), the leaf of Marsilea is pinnately 

compound, with four pinnules borne on the slender rachis; two pinnules are 

noticeably higher than the other two, and are inserted on the rachis in 

alternate fashion. A leaflet has many dichotomously branched veins, which 

are joined with each other by transverse bands and their ends unite to form 

marginal loops (Fig. 2).

Fig. 2 Dichotomously branched and petiolate leaves of Marsilea sp. 

At the base of the petiole many bean-shaped or oval and stalked 

sporocarps develop (Fig. 3). 

Fig. 3 Bean-shaped or oval and stalked sporocarps at the base of petioles in Marsilea 

sp.

Anatomy of Marsilea 

Rhizome (Stem) 

Epidermis is single-layered, made up of compactly arranged thick- 

walled cells. 

Cortex is differentiated into three regions, viz. outer cortex, the middle 

cortex and the inner cortex: 

a. outer cortex is aerenchymatous, one to several cells in 

thickness, sometimes also consists of tannin cells, 

b. middle cortex consists of sclerenchymatous tissue filled with air 

cavities arranged in the form of ring, and 

c. inner cortex is solid tissue of several cells in thickness. The 

inner layer of inner cortex is parenchymatous, filled with starch, 

while outer region of inner cortex is sclerenchymatous in nature. 

The vascular cylinder is siphonostele; limited externally and internally 

by endodermis, hence called outer endodermis and inner endodermis, 

respectively. 

The siphonostele is medullated. The xylem is in the form of ring. 

Phloem is present on both sides of xylem. Such a stele is called 

amphiphloic siphonostele. 

The deposition of the several tissues from inwards is outer endodermis, 

outer pericycle, outer phloem, xylem, inner phloem, inner pericycle and 

inner endodermis (Fig. 4).

Petiole 

Fig. 4 Marsilea: Transverse section of rhizome; a part cellular 

Single layered epidermis made up of rectangular cells. 

The outer cortex consists of few layers of thin walled cells; middle 

cortex is aeranchymatous consisting of ring of air-chambers; while the 

inner cortex is a solid, compact tissue several cells deep. The inner 

layers of inner cortex are paranchymatous and filled with starch. Here 

and there tannin-filled cells also occur. 

The stele is covered externally by a single-layered distinct endodermis. 

It is triangular in outline, lies in the centre, and has a single vascular 

bundle. The xylem is ‘V’ shaped, with opening towards the axis. 

The order of the tissues from inner to outer side of the stele is xylem, 

xylem parenchyma, phloem, pericycle and endodermis (Fig. 5).

Leaflet 

Fig. 5 Marsilea:Transverse section of petiole; a part cellular 

It consists of upper and lower epidermal layers, each made up of a 

single layer of paranchymatous cells. The continuity of epidermis is 

interrupted by slightly sunken stomata. Stomata are restricted to the 

upper epidermis in floating leaves. 

The ground tissue (mesophyll) lies between the upper and lower 

epidermis and is differentiated into palisade and spongy parenchyma: 

The palisade part lies just beneath the upper epidermis and consists 

of columnar cells rich in chloroplasts, while the spongy part faces 

the lower epidermis and consists of rounded cells 

In case of submerged species, there is no distinction between 

palisade and spongy tissues.

Root 

Vascular bundles are embedded in the mesophyll tissue. They are 

concentric in nature. Each bundle has a central core of xylem, 

surrounded by phloem. 

The arrangement of tissues in the stele is xylem, phloem and bundle 

sheath (Fig. 6). 

Fig. 6 Marsilea: Transverse section of lamina. 

It consists of piliferous layer instead of epidermis, made up of 

compactly arranged biconvex cells. 

Beneath piliferous layer, the cortex is made up of an outer cortex and 

inner cortex: 

Outer cortex is aerenchymatous, consisting of large air chambers 

arranged in the form of ring. 

Inner cortex is compact, made up of rounded cells containing starch. 

Inner cortex is delimited by a single layer of distinct endodermis.

Vascular bundle lies within the endodermis, and is usually diarch and 

exarch. 

The xylem is plate-like and occupies the centre of stele. The 

protoxylem, consisting of two small mass of cells, is towards the 

periphery (pericycle), while metaxylem is large, plate-like and occupies 

the centre. 

There is no medullary tissue (pith) in the stele and arrangement of 

tissue is metaxylem, protoxylem, phloem, pericycle and endodermis 

(Fig. 7). 

Fig. 7 Marsilea: Transverse section of root. 

Reproduction in Marsilea 

Marsilea is a sporophyte and reproduces asexually both by vegetative means 

as well as by means of spores. 

Vegetative reproduction: In Marsilea, vegetative reproduction occurs by the 

formation of tubers, which are small, bud-like structures containing reserve 

food material, arising from some subterranean branches of the rhizome.

These tubers serve as perennating organs, and are capable of tiding over the 

unfavourable conditions. On the return of favourable conditions, these tubers 

germinate to form new plants. Tuber formation has been reported in a few 

Marsilea species, such as M. minuta and M. hirsuta. 

Reproduction by spores (spore formation): Marsilea is a heterosporous 

fern, which produces two types of spores – microspores and megaspores in 

separate sporangia, borne in special bean-shaped bodies called the 

sporocarps. 

Sporocarps: Sporocarp is a bean-shaped to ovoid, nutlike structure, attached 

to the basal part of the petiole with the help of a stalk. It is green and soft 

when young, but turns dark-brown at maturity. Usually one sporocarp is 

present at the base of each petiole, but in some species, the number varies 

from 2 – 20. Sometimes, the attachment of sporocarps with the petiole shows 

so much variation that different species can be distinguished on this particular 

character (Fig. 8); for example in M. polycarpa many sporocarps are attached 

on one side of the petiole in a single vertical row. In M. quadrifolia, pedicels 

(stalks) are united with one another, and then jointly inserted on the petiole. In 

M. minuta, the stalks of all the sporocarps though free, are attached to the 

petiole at a single point.

Fig. 8 Marsilea: different modes of attachment of sporocarps to the petiole – A, 

M. polycarpa; B, M. quadrifolia; C, M. minuta; and D, M. vestita. 

Structure of sporocarp: The sporocarp is differentiated into a stalk (pedicel) 

and a body. The stalk is fused laterally to the back of the body of the 

sporocarp, generally forming a distinct ridge called ‘raphe’. In some species, 

the distal (upper) end of the raphe is marked by one or two teeth-like 

projections, known as tubercles. 

Internal structure of the sporocarp: The internal structure of the sporocarp 

can be studied under the following headings: 

Sporocarp wall: The wall of the sporocarp is very hard, thick and highly 

resistant to mechanical injury. It is differentiated into an outer epidermis, a 

middle hypodermis, and an inner paranchymatous zone. The epidermis is 

made up of cuboidal cells, covered with a thick layer of cuticle. A large 

number of sunken stomata are present in the epidermis. The hypodermis 

consists of two layers of radially-elongated palisade-like cells, which are 

compactly arranged without any intercellular spaces between them. The inner 

paranchymatous cells of this zone form a gelatinous ring inside the sporocarp 

wall (Fig. 9). 

Fig. 9 Transverse section of the wall of Marsilea sporocarp: A, young stage; B, old 

stage. 

Sori: When we cut the horizontal section of sporocarp, a ring appears in the 

form of a dorsal and a ventral mass. In this plane, both micro- and

megasporangia are visible as sori. The sori are the reproductive structures 

arranged in the two alternating rows in the cavity of the sporocarp (Fig. 10). 

Each sorus has a receptacle which contains one terminal megasporangium 

and two microsporangia on the lateral sides. It is surrounded by an indusium. 

The sori overlap each other and the indusia of adjacent sori are partially 

fused. 

Fig. 10 Marsilea sp.: A, Vertical transverse section of sporocarp; B, horizontal 

longitudinal section of sporocarp. 

The number of sori in a sporocarp varies from two in M. aegyptica to twenty in 

M. quadrifolia and M. vestita. There are 11 – 12 sori in M. minuta. 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. The number of micro- and megasporangia 

varies with species. In M. minuta, a sorus has 4-8 megasporangia and 8-13 

microsporangia. 

Development of sporocarp: Sporocarp originates from one of the marginal 

cells of a very young leaf, when it is 6-8 cells high. One of the marginal cell 

cuts off segments on either side and one of the derivatives acts as the apical

cell for the second sporocarp. This process is repeated several times 

depending on the number of sporocarps formed at the base of a leaf. The 

sporocarp, initially cuts off segments on either side and forms a mass of 

undifferentiated cells, which later curves markedly so that its distal end is 

directed in a horizontal plane. Subsequently, two rows of soral mother cells 

are differentiated on the ventral side of the young sporocarp. The differential 

growth of soral mother cells and their derivatives, results in the formation of 

involutions on the upper surface of the sorus. These involutions grow into arc- 

shaped depressions called soral canals. The soral mother cells divide to form 

receptacular surface in the alternating rows. The sporangial initial develops on 

the receptacular surface in acropetal succession, i.e. first sporangial initial is 

formed at the apex of receptacle and it forms megasporangia. Subsequently, 

two initials are formed on the lateral sides of the receptacle. They functions as 

microsporangial initial, each forming a microsporangium (Fig. 11).

Fig. 11 Diagrams showing developmental stages of micro- and megasporangia of 

Marsilea sp. 

Development of sporangia: Since Marsilea is a heterosporous fern, 

megasporangia (macrosporangia) produce megaspores and the 

microsporangia produce microspores. The sporangia develop in a 

basipetalous manner on the receptacle. The megasporangia develop first at 

the top of the receptacle and are, therefore, older, while the microsporangia 

develop later along the sides of the receptacle. The development of 

microsporangium, as well as of megasporangium is almost similar. The 

sporangial initial divides transversely, forming an outer and an inner cell. The 

entire sporangium develops from the outer cell, the inner cell taking no part in

its development. The outer cell of sporangium, which is destined to form 

spore mother cell, undergoes repeated divisions. Each spore mother cell 

undergoes reduction division and forms four haploid spores. In 

megasporangia, all but one spore degenerates to form a nutritive liquid, which 

grows in size at the expense of others, forming a single large functional 

megaspore (Fig. 12). In microsporangia, almost all the spores in a 

microsporangium are functional. They are smaller in size. 

Fig. 12 Marsilea sp.: mature megaspore within the megasporangium, showing very 

thick and well-differentiated wall. 

Dehiscence of sporocarp: There is no special mechanism for the liberation 

of sporangia from the sporocarp. They are set free only when the wall of the 

sporocarp splits open. As the sporocarp breaks at one point due to absorption 

of water, the sori come out along the gelatinous ring of sporocarp (Fig. 13). 

These sori function as mother cells of the gematophytic generation.

Fig. 13 Diagrams showing stages in the dehiscence of Marsilea sporocarps. 

Gematophytic generation 

The microspores and the megaspores germinate separately to produce 

male (micro-) and the female (mega-) gametophytes. The microspores 

germinate immediately after shedding, forming small biconvex prothallial cell 

and a large apical cell. The apical cell by repeated divisions ultimately forms 

androcytes or antherizoid- mother cells. Each androcyte metamorphoses into 

a cork screw-shaped multiflagellate antherizoid, characterized by the 

presence of a prominent terminal vesicle (Fig. 14). 

Fig. 14 Marsilea: screwshaped 

multiflagellate antherizoid, characterized by 

the presence of a prominent terminal vesicle. 

Similarly, megaspore undergoes division, forming small nipple-shaped 

apical cell and a large basal prothallial cell. The apical cell forms the female

gametophyte, while prothallial cell provides nutrition to the developing 

gematophytes (Fig. 15). 

Fig. 15 Marsilea: germination and development of the female 

gametophyte. 

Fertilization: The neck canal cells and the ventral canal cell degenerates to 

form a mucilaginous mass, which attracts sperms chemotactically. One of the 

sperms fuses with the egg to accomplish fertilization and form the diploid 

zygote. The zygote is the mother cell of the next sporophytic generation and 

develops into a young sporophyte within 2-4 days after fertilization. 

Embryogeny: The fertilized egg (zygote) enlarges in its size and secretes a 

thin cellulose wall around it. It enters into rapid divisions, to give rise to a 

young sporophyte within 2 - 4 days. Zygote divides vertically and produces 

two unequal cells. The larger cell is known as the epibasal cell, and the 

smaller one as the hypobasal cell. These two cells undergo transverse 

divisions to form a quadrant embryo. The cells of the quadrant embryo show 

definite relation to the primary growth of the embryo. Epibasal half produces

shoot and leaf. Hypobasal half produces root and foot. Hence the 

development is described as lateral. In quadrant embryo, the next divisions 

are irregular. At the time of differentiation of different primordia in the embryo, 

the adjoining cells of megagametophyte divide periclinally, forming a thick 

calyptras, which encloses and protects the developing embryo. The calyptra 

is greenish in colour. Large number of rhizoids may develop from the base of 

calyptra. The embryo gives rise to the young seedling that penetrates through 

the calyptra and grows into a sporophyte (Fig. 16). 

Fig. 16 Marsilea: stages in the development of embryo - A-E, early developmental 

stages; F, mature female gametophyte bearing young embryo surrounded by the 

calyptra; G, median-longitudinal section of the mature female gametophyte. 

Life cycle: In the life cycle of Marsilea, we find alternation of generations. 

Marsilea plant is a sporophyte, which is the dominant phase in the entire life 

cycle. The sporophyte comprises rhizome, roots and leaves. It reproduces 

vegetatively, as well as by means of spores. The spores are formed in 

sporangia on specialized structures called sporocarps. The sporocarps bear 

two kinds of asexual spores which are formed after meiosis and are, thus 

haploid (meiospores). The smaller spores are known as microspores. They 

are produced within microsporangia. The larger spores are known as 

megaspores, which are formed in the megasporangia. Both the sporangia are

produced within the fruit body, the sporocarp. The whole life cycle of Marsilea 

is depicted in Fig. 17. 

Fig. 17 Marsilea: diagrammatic representation of life cycle.

Morphology of Marsilea Systematic position Kingdom : Plantae - CEC

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