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Home , Sporocarp (ferns)

Marselia- Water

Dr. Pallavi J.N.L. College Khagaul Distribution and Classification • Marsilea is commonly known as “water clover” or “water fern” (although it is a fern but hardly resembles a true fern). • Either the species are hydrophytic or amphibious i.e., they grow rooted in mud or marshes and shallow pools or are completely submerged • CLASSIFICATION Division- Pteridophyta Class- Filicopsida Order- Hydropteridales Family- Genus- Marsilea Morphology: • Plant body is sporophytic and herbaceous plant. The plant body is differentiated into rhizome, and roots. Rhizome: • All the species possess a rhizome which creeps on or just beneath the soil surface. It is slender, dichotomously branched with distinct nodes and internodes and is capable of indefinite growth in all directions. Leaves: • They are borne alternately on upper side of rhizome at nodes, in two rows. They show circinate vernation. In submerged plants the petiole is a long and the lamina floats over the surface of water but in muddy or marshy plants the petiole of the is short and rigid with short lamina spreading in the air. • The lamina consists of 4 leaflets/pinnae which are present at the apex of petiole. Near the base of petiole the stalked bean-shaped sporocarps are borne. Roots: The roots are adventitious, arising from the underside of the node of rhizome, either singly or in groups. Anatomy T. S. Rhizome (stem): Young rhizome is protostelic in nature i.e., pith is absent and xylem is completely surrounded by phloem ,however, in older stem pith is developed in the centre and the stele becomes amphiphloic siphonostelic type. Thus, internally rhizome consist of epidermis, cortex, followed by stele which is made up of outer endodermis, outer pericycle, outer phloem, xylem, inner phloem, inner pericycle and inner endodermis. T.S. leaflet: T. S. of the leaflet shows upper and lower epidermis, in between mesophyll tissue is present (differentiated into palisade and spongy parenchyma) and vascular bundles. In submerged species mesophyll region is not differentiated into palisade and spongy parenchyma. T. S. Root: T. S. of root is circular in outline and can be differentiated into epidermis or piliferous layer, cortex and stele (Protostelic).

Reproduction Marsilea reproduces by two methods: (i) Vegetative/Asexual reproduction • It takes place by means of tubers which are produced in dry conditions from the rhizome. First a branch is given out from the rhizome, which later on swells up due to the accumulation of food material. The structure is termed as tuber and is capable of tiding over the unfavourable conditions. On the return of favourable conditions it germinates to produce a new sporophytic plant, e.g. ,M. hirsuta, M. quadrifolia. (ii) Sexual Reproduction: Sporophytic Phase: producing organs: • Marsilea is heterosporous i. e., it produce two types of — and . These spores are produced in microsporangia and megasporangia, respectively. These sporangia are borne in special type of spore producing organ called sporocarp. The sporocarp are born laterally on the short and lateral branches (peduncle) of the petiole of leaf either near the base or a little higher up. • They arise solitary or in clusters. Number of sporocarp differs in different species and varies from 1 to 20 or more. Each sporocarp is an oval or bean shaped biconvex, flattened structure. It is green and soft when it is young but at maturity it becomes very hard and brown in colour. Development of sporangia: • The development of micro and megasporangia is of lepto-sporangiate type. The leptosporangiate differ from other in having a with a jacket layer one cell in thickness. There is a definite number of spores within a sporangium. The sporangium develops from a single initial cell and the tapetum differentiates from a single internal cell of a developing sporangium. Dehiscence of Sporocarp and Liberation of Spores: The decaying of the wall of the sporocarp takes place due to bacterial action and thus the sporangia and spores are liberated. The sporocarp bursts open only in water. The gelatinuous ring absorbs water and extends greatly through the open margins of the sporocarp thus dragging out sori along with it. The gelatinous ring bears two alternating rows of sori. The delicate mucilage wall of the sporangia (micro-or mega) opens in water and the spores (micro-or mega are liberated which germinate soon Gametophytic Phase: • The microspores and the megaspores are the unit of male and female gametophytes respectively. • They germinate to produce the respective gametophyte in the following ways: Development of male gametophyte: • The is the initial stage in the development of male gametophyte. Each microspore is a unicellular, uninucleate, thick walled globose and haploid structure. • The cytoplasm is surrounded by inner wall called endosporium and outer wall called exine or exosporium. The microspore germinates just after its liberation. The first division is in a lenticular plane to form a small lens shaped prothallial cell and a apical cell. • The apical cell divides transversely to form 2 equal antheridial initials. Each antheridial initial divides periclinally to form an outer first jacket cells (initial) and inner wedge- shaped sister cells. The inner cell further divides by periclinal division to form a second smaller jacket cell and a large outer cell. • The large cell again divides by a periclinal wall to form an outer or peripheral third jacket layer and a central cell or the primary androgonial cell. Each primary androgonial cell divides to form 16 androcytes (Sperm mother cells) and finally metamorphosises into antherozoids. In all 32 antherozoids are produced. Development of Female Gametophyte: • The is an oval or elliptic structure, the wall of which imbibes water and expands to form a gelatinous mass around the megaspore. About two or three hours later of the beginning of the spore , the nucleus divides which is soon followed by a transverse division. • This transverse wall develops in between the denser cytoplasm of the protuberance and the remaining watery cytoplasm. The small cell lies within apical protuberance. The lower large cell is nutritive or prothallial cell and occupies the remaining large portion of the megaspore. The large prothallial cell is quite vegetative and does not divide further. • This large cell functions as store house of food material. The small cell situated within the apical papilla develops into the gametophyte proper. • All the four segments divide by anticlinal divisions several times giving rise to a one-celled thick vegetative tissue. The archegonial initial divides periclinally forming a primary cover cell and central cell. The primary cover cell further divides by two successive anticlinal divisions forming four quadrately arranged neck initials. • Each neck initial divides by an oblique wall forming a short neck comprised of two tiers of four cells each. Simultaneously, the central cell divides into two cells, a small primary canal cell and a large primary venter cell. In M. drummondii and some other species the primary canal divides producing two small canal cells. • In all species the primary venter cell divides into two cells, a small venter canal cell and a large spherical oosphere or egg. On the maturation of the archegonium the neck canal cell or cells and the venter canal cell disintegrate and the archegonial neck remains open. Fertilization: Many antherozoids are attracted towards the funnel shaped structure of megagametophyte. The antherozoids enter gelatinous envelope and reach to the archegonium. Only one antherozoid enters the egg’s cytoplasm and fuses with the egg nuceus to form zygote. Development of Embryo into new sporophyte: The zygote is the mother cell of the next sporophytic generation. The first division of the zygote is vertical followed by a transverse division resulting in the quadrant stage (four-celled stage) of the embryo. Subsequent development of the upper two cells forms the root and leaf, whereas the lower two cells give rise to the foot and shoot apex