Marchantia is a family of liverworts belonging to the Marchantiaceae, and Marchantiales.
Marchantia’s thallus shows two layers of differentiation: one is the upper photosynthetic layer, which has pores and well-defined epidermis. The lower storage layer is less defined. Gemmae are tiny tissue packets that can be used for asexual reproduction. The thallus is made up of small cups-like structures known as gemma cups. The combination of the barrel-shaped pores and circular shape of gemma cups is indicative of the genus. The ventral surface of thallus contains multicellular purple-colored scales with single-cell thickness and unicellular Rhizoids.
Classification of Marchantia
Marchantia is home to about 65 species. It is widely distributed around the globe. This genus is mostly restricted to temperate areas and can grow in moist, cool, and shaded places. There are 11 species of Marchantia that have been identified in India. They are found mainly in the Himalayas, and very few species can be found in plains or hills. These include M. polymorpha and M. nepalensis as well as M. palmata.
- Habitats that are both moist and shaded are the common habitat.
- The plant body is thalloid. The thallus is flat, dorsiventral and dichotomously branching. The dominant phase of plant life is the gametophyte.
- The dorsal surface has diamond-shaped markings. It also contains a central pore for gaseous exchange. Under the polygonal markings, there are chambers.
- There are scales on the ventral surface. Rhizoids are unicellular, and have a root-like structure. Its main function is to anchor the plants to the substratum, and to absorb water and minerals.
- On the dorsal surface, you will find the reproductive bodies.
- Gemmae is a cup-shaped structure that allows for sexual reproduction.
- The stalks, called archegoniophore or antheridiophore, are home to sexual reproductive organs. They are home to the male and female reproductive organs archegonia and antheridia, respectively.
- The epidermis’ upper layer is composed of air pores. These air pores open into the photosynthetic area’s air chamber. There are also very few chloroplasts in the upper epidermis.
- The storage zone is located beneath the photosynthetic and air chambers. It is composed of parenchymatous cells and lacks chloroplasts. They store starch, protein, oil, and mucilage.
- The lower epidermis is where the scales and rhizoids are located.
Structure of Marchantia (With Diagram)
1. External structure
Marchantia’s plant body is thallus-like, flat, dorsiventrally distinct, and densely dichotomously branching. Each branched has a notched apex. The thallus is dark-green in colour, and has a midrib. The gemma cup is a cup-shaped structure that can be found on the dorsal surface of the midrib. This structure appears as the thallus reaches maturity. Mature thallus bears bear certain specialized sexual organs, such as antheridiophore or archegoniophore. These organs bear in them antheridia (malesex organs), and archegonia. organs) respectively.
2. Internal structure
The thallus of Marchantia internal shows different types of tissue differentiation –
(a) Epidermal Region
It is composed of a well-defined upper and lower epidermis. The epidermis’ upper layer forms a protective layer on the photosynthetic area. It consists of thin-walled cells with thickened outer walls. Few chloroplasts are found in epidermal cells. Special air pores with barrel- or chimney-shaped shapes are embedded in the epidermis.
(b) Photosynthetic Region
The air chambers are located beneath the epidermis. They are composed of one horizontal layer. Each chamber is bounded by a thin one-cell layer partition. They are 3 to 4 cells high. Through a barrel-shaped pore or chimney-like port, each chamber can communicate with the outside. Each chamber contains short, simple, or branched green cell filaments, also known as photosynthetic or assimilatory filaments. Many ovoid chloroplasts are found in photosynthetic filament cells.
(c) Storage Region
The storage area is located just below the photosynthetic zone. It tapers towards the edges and is thickest at the center. It is composed of uniform tissue that is made up of large, colourless, thinwalled, polygonal, parenchymatous, cells. These cells lack chloroplasts, but they do contain starch and other protein grains. The cells can be isolated and may contain one large oil body, or they may be filled with muclage. These cells are later called mucilage cells. The storage region’s lower region contains cells that are similar to the upper epidermis. It is the lower epidermis. It projects the scales and rhizoids.
Marchantia’s thallus reproduces by both vegetative and sexual means.
1. Vegetative Reproduction in Marchantia
The following steps are used to reproduce vegetative plants:
It all depends on how old the vegetative cells are. The older cells die from old age, and eventually become disorganized. The young lobes are separated when the decay and dead of the older portions reach the dichotomy. Each one of these is transformed by apical growth into a new, larger thallus.
(b) Adventitious Branches
These can develop from any area of the thallus, but especially the ventral surface. It was reported that Marchantia palmata developed adventitious branches by utilizing the stalk and disc from the female gametophore. They are formed by the decaying of the connecting tissue, and become separate from the parent thallus.
(c) Gemmae Formation
Marchantia can also reproduce by the formation of multicellular bodies, called the gemma. Gemmae can be produced in large numbers inside a cup-like structure called the gemma cups, which is borne on the gametophyte’s dorsal surface along the midrib. After detaching from the gemma cups, each gemma germinates into a new plant in favourable conditions.
2. Sexual Reproduction
Marchantia can be described as heterothallic, i.e., it is dioecious. The archegonia in the female plant are carried on special, erect stalked branches called archegoniophore. In the male plants, the antheridia are carried on an erect stalked branch called Antheridiophore.
Each archegoniophore is born from the region just below the thallus’ apex. A mature archegoniophore is a stalk with a distinct, usually 8-rayed or lobed, stellate disk at its apex. The rays are divided into radial rows. Each row is carried in an inverted orientation. Each archegonium has a flask-shaped structure. It consists of a narrow neck, several neck canal cells, and a swollen ventr which contains a ventral cell cell and an egg. Attached to each archegonium is a stalk that runs from the disc’s lobe.
Each antheridiophore has a similar position to the archegoniophore. It is composed of a stalk measuring between 1-3 cm in length and a disc measuring 8 lobes at its apex. Flask-shaped cavities are found towards the top of the disc. A mature antheridium is a pear-shaped, or globular body. It has a short stalk and a jacket layer made up of one layer of thinly walled cells. Many androcyte mother cells are found within the antheridial coat. Each androcyte mother cell splits diagonally into two triangular androcytes, or antherozoid mothers cells. Each androcyte eventually metamorphoses into biflagellate Sperm, i.e., an antherozoid.
It occurs in the presence of water. Rainwater is often sprayed onto the slightly elevated archegoniophores to splash the antherozoids. The antherozoids swim in the water and eventually reach the egg. One sperm merges with the egg when it reaches the egg. A diploid zygote (2n), is formed as a result. Diploid sporophytic generation starts with the formation of zygote.
The sporophyte’s first cell is the zygote. The zygote grows rapidly in size and almost fills the ventral cavity immediately after formation. The ventr cell also divides and redivides, forming multiple layers of calyptra that surrounds the developing sporophyte. The venter cells also divide and redivide, forming a collar-like outhgrowth of one-celled thickness known as pseudoperianth, or perigynium.
The zygote’s nucleus divides transversely first into two cells: an upper epibasal and lower hypobasal. Another vertical division occurs so that an 8-celled structure, i.e., the octant, is formed. The capsule and upper portion of the seta are formed by derivatives of epibasal cells, while hypobasal cells give rise to the lower section of the seta and foot of the sporophyte. The epibasal cells undergo periclinal divisions, which results in the formation of outer amphithecium (or inner endothecium) and sporogenous cells. The capsule’s single-layered jacket is made up of amphithecium and endothecium. Sporogenous cells are formed by the latter. Half of all cells that are produced by the endothecium form spore mother cell cells. The remaining cells become sterile and develop long, tapering cells known as elaters. Each meiotic division of a spore mother cells results in four haploid (spore-tetrad) spores.
The mature sporophyte has a more or less long structure. It can be divided into three distinct regions: seta, foot, and capsule. The archegonium base is a bulbous, or anchor-shaped, spreading foot. The seta, which is both short and thick, lies between the capsule and foot. The capsule has a nearly oval or spherical shape and is covered with single-layered cells. The capsule also contains inside spores, elaters.
The spore is released and germinates in a favorable environment, producing a germ tube that gives rise to a new Marchantia plant.
Structure of the Mature Sporophyte
Marchantia’s mature sporophyte is divided into three parts: seta, foot and capsule.
It is a bulbous, expanded mass of cells located at the base the sporogonium. It serves as an anchoring and absorbing organ. It absorbs nutrients from gametophyte.
It’s a stalk with a slight elongated shape that connects the capsule to the foot. These cells are parenchymatous, and they grow in length. Seta is a lengthening process that pushes the mature capitula out of the calyptra.
It is a yellow-colored spherical structure that contains many spores. Three covers protect the capsule: Perichaetium and calyptra-perigynium protect the capsule.
Dehiscence of the Capsule:
The jacket of the mature hanging sporogonium capsule (capsule), is dried and splits longitudinally to form a variable number if longitudinal lobes. These lobes run from the apex of the capsule to the middle. Due to their hygroscopic nature, the coiling and uncoiling elaters aid in the dispersal and discharge of sport to the atmosphere.
The spores are small and round, measuring between 12 and 30 um in diameter. They have a thin outer exine and an inner intine that are slightly thicker. Some species also have a layer outside of the exine called perispore.
Life cycle of marchantia
Marchantia exhibits alternation of generation. The haploid sexual phase and the diploid asexual stage alternate. Marchantia’s life cycle is haplodiplontic. Multicellular structures are used to represent both the diploid and haploid phases.
The gametophyte (haploid) is the main free-living plant body. The gametophyte is the anchorage and food source for the short-lived sporophyte stage (diploid).
Antherozoids and eggs are formed by the male and female gametophytes. These fusions form the diploid fertile zygote. To form a multicellular organism, the zygote divides through mitotic division. The spore mother cells divide through meiosis to create the haploid seed, which then germinates to become the haploid gametophyte.