Life cycle of Marchantia

Marchantia : General Description of Structure and Reproduction Process

Marchantia
 
It is one of the important species of Liverworts. It is widely distributed, commonly found in moist and shady places. There are about 65 species of marchantia. In Nepal there are three species found Marchantia palmate, M. nepalensis, M. polymorpha. 

Gametophyte 
External Structure 

• The plant body is thalloid. The thallus is dorsoventrally flattened, prostrate, and dichotomously branched. 
• On the dorsal surface there is dark green colored mid rib. 
• The mid rib bears gamma cup for asexual reproduction 
• The ventral surface consists of unicellular, tubular, colorless structures called rhizoids and multicellular plate like violet in colour structures are present called scales. 
• The rhizoids absorb water. They are of two types 
1. Smooth rhizoids which are thin walled. 
2. Tuberculate rhizoids which are thick walled 
• The scales protect from the injuries to the thallus and transport water. The scales are simple and complex. 
• At the apex of the thallus there is apical notch. 
• The male and female plants are found separately i.e. dioecuious. 
• In male plant male sex organs, Antheridia are produced and in Female plant female sex organs, archegonia are produced. 
Internal structure 
• On the dorsal and ventral surface of the thallus outermost single layered epidermis is present. 
• The upper epidermis consists of air pores 
• The air chambers are present below upper epidermis. 
• The air chambers are separated by partition walls. 
• In air chamber there are photosynthetic filaments which are made up of cells which are rich in chloroplast where food is synthesized. It is synthesizing zone. 
• Below synthesizing zone, there is a region of compactly arranged paranchymatous cells, which are thin, walled that store food. It is storage zone. 
• Lower epidermis consists of number of rhizoids and scales. 
Reproduction 

By fragmentation 

In this older region of thallus decayed or degenerate and younger region or apical region again regenerate and produce new plant body. 

By adventitious branches 

In this method, branches develop on the ventral surface of thallus. Now branch grows into new plant body. 

By gemmae 

The cup like structures is found on the midrib of dorsal surface. Within gemma cup small stalked structures are formed called gammae. The gammae are asexual reproductive structures, which are made up of parenchymatous cells. On the lateral side of gemmae notch is present. The cells of the gammae are filled with chloroplast. When the gemmae fall on the ground, they produce new plant body. 

Sexual Reproduction 

The Marchantia is dioecious or heterothallic i.e. male and female sex organs are found in separate individual. The male sex organ is found in male plant and female sex organs are found in female plant. The sexual reproduction takes place by fusion of male and female gamete. 

Male gametophyte 
• The male gametes are called antherozoids. Each antherozoid is elongated, coiled, and flagellated. Anhterozoids are formed within male sex organ called antheridium. Each antheridium is globular with short stalked and jacket layer encloses numerous cells called androcytes. 
• Each androcytes forms antherozoids when antheridium gets ruptured and therozoids liberate out. The antheridia are fond on the upper surface of the receptacle of antheridiophore. 
• Each anterridium is embedded in a cavity. The cavity opens outside through a pore called ostiole. The antherozoids come out through ostiole and swim in water. 
Female gametophyte 
• The female plant bears archegoniophore. It is 5-7 cm long. It consists of stalked and star like female receptacle. Usually receptacle has nine rays of star like structure. 
• Numerous female sex organs called archegonia are hanging in lower part of female receptacle. 
• Archegonia consists swollen basal portion called Venter and elongated neck. 
• The Venter consists of a prominent cell called egg. Near egg, there is another cell and Venter canal cell. Cell in the neck are called neck canal cell. 
Fertilization 
Swimming antherozoid reach to the archegonia tip with the help of water. Neck canal cell of archegonia gets dissolved. A kind of mucilage is secreted by dissolving neck canal cells and reaches to the venter canal cell and gets fused with egg and zygote is formed. 

Sporophyte 
• The zygote undergoes number of cell division during development and the structure of zygote at that stage is called sporophyte. 
• The basal portion of the sporophyte is called foot and middle elongated portion is called seta. 
• Round globular terminal part is called capsule which consists of thread like elaters and number of unicellular spores formed by meiosis division in spore mother cells within capsule. 
• The capsule is surrounded by a layer called jacket. 
• The whole sporophyte is surrounded by layer of cell called calyptra. Elaters help in spore discharge when jacket or capsule is ruptured. 
• The sporophyte is parasitic because it depends up on female gametophyte. 
• Half of the spores germinate produce male gametophyte and half germinate to produce female gametophyte.