Liverwort

The liverworts are bryophytes in which the plant is green, dorsiventral thallus. They are also known as hepaticopsida. The name of this class is derived from a latin word hepatica which means liver, hence the member of this class is commonly called liverworts. This class includes about 280 genera and 9500 species. 

1.0General Characteristics of Liverworts

• Plant body is gametophytic and the gametophyte is either thalloid or foliose, thalloid forms are prostrate, lobed, dorsiventral and dichotomously branched. In foliose forms, ‘leaves’ are entire, lobed or divided and without ‘midrib’. ‘Leaves arranged in two to three rows on the axis.
• The gametophyte is secured to the ground by simple, unicellular absorptive processes called rhizoids.
•  Photosynthetic cells contain many chloroplasts. Pyrenoids are absent.
• Sex organs are exogenous in origin and are either dorsal in position, or terminal. Each sex organ develops from a single initial cell; they may be superficial or embedded in gametophytic tissue. Members may be monoecious or dioecious.
• Sporophyte is either simple or represented by capsule only (e.g., Riccia) or may be  differentiated into foot, seta and capsule (e.g., Marchantia).
• Sporogenous tissue either forms only spores (e.g., Riccia) or is differentiated into sterile elater mother cells and fertile spore mother cells.

2.0Habitat of Liverworts

Liverworts prefer to grow in humid, shady and in soil where moisture is abundant. They are not adapted to grow in dry habitats as the plant body is not evolved against serious desiccation. 

3.0Reproduction in Liverwort

Liverwort reproduces by means of vegetative and sexual reproduction. Asexual spores (mitospores) are not seen yet.

Vegetative Reproduction in Liverworts

• Fragmentation : "In liverworts, the process of fragmentation involves the natural disintegration and separation of older cells or specific parts of the thallus due to aging. As a result, young thallus lobes, known as fragments, are created. As this process continues towards the point of dichotomy, the lobes of the thallus separate. The detached lobes or fragments can further develop into independent thalli through apical growth."
• Gemma : The gemma cups are circular or crescent-shaped. The gemmae are produced in the gemma cups which are found on the dorsal surface of the thallus, they may be circular or crescent-shaped. Mature gemmae are found to be attached at the base of the gemma cup by a single stalk. After falling on suitable substratum gemma germinate to form a new plant.  The gemma cups are circular or crescent-shaped.

Sexual Reproduction in Liverworts

Sexual reproduction in liverworts consists of union of gametes and subsequent production of meiospores. The male and female sex organs in some species of liverworts develop on the same thallus such species are called monoecious while in some species the male and female sex organs develop on different thallus such species are called dioecious. They are either embedded in the tissues of thallus or raised on special upright branches. 

Sporophyte : After the fertilization the zygote develops into the second individual in the life cycle called sporophyte which is also known as sporangium. In the life cycle of liverworts, as well as in other bryophytes like mosses and hornworts, the sporophyte generation is largely dependent on the gametophyte for nutrition and support. 

In some species the sporangium is differentiated into foot, seta and capsule while in other seta and foot is absent. 

4.0Classification of Liverworts

Schuster (1957) divided the class Hepaticae into two sub-classes:

Sub-class 1. Jungerinanniae. It includes four orders:

• Order 1.Calobryales 
• Order 2.Takakiales 
• Order 3.Jungermanniales 
• Order 4.Metzgeriales 

Sub-class 2. Marchantiae: It includes three orders:

• Order 5.Sphaerocarpales
• Order 6. Marchantiales 
• Order 7. Monocleales