Anthoceros Life Cycle, Sexual and Asexual Reproduction and Structure

Anthoceros belongs to;

This genus contains about 200 species, which are distributed all over the world, especially abundant in moist areas of tropical and temperate regions of earth.

Anthoceros Structural Features:

External Structure (Morphology):

Like other bryophytes the dominant generation of Anthoceros is gametophyte. Gametophyte of Anthoceros is dark green in color and has grassy look. It has prostrate stem. This stem shows dichotomous branching. Margins of these branches have lobes. Surface of gametophyte may be hairy, spiny or have ridges. From the ventral side of gametophyte of Anthoceros, rhizoid emerges, which anchor this plant in soil and absorb nutrients for thallus (gametophyte).

Internal Structure (Anatomy):

There is no much differentiation of tissues in gametophyte of Anthoceros. Whole thallus is formed of parenchymatous cells. The dorsal side is lined with upper epidermis and ventral side is lined with lower epidermis. The cells just below upper epidermis contain single lens shaped chloroplast, while deeply situated cells contain 2-4 chloroplasts. Lower surface of gametophyte has cavities which contain Nostoc species, these bacteria fix nitrogen.

Anthoceros Life Cycle (Reproduction)

Anthoceros reproduce by sexual as well as by asexual methods.

Asexual Reproduction (Vegetative Reproduction):

• Death of older parts of thallus away from the apex of branches cause the separation of branches, each branch is capable of producing new plant.
• Under unfavorable conditions, the margins of branches of gametophyte become swallow due to storage of food. Unfavorable conditions cause the death of branches but swollen portion survives and restart its growth during favorable conditions and produce new plant.
• In some species of Anthoceros, during summer the whole plant die, except for apices. These apices produce new plants when summer passed away.
• Some species of Anthoceros also produce gammae on short stalks on dorsal side of gametophyte. These gammae after getting separated from thallus, produce new plant.

Sexual Reproduction (Life Cycle):

Most species of Anthoceros produce male and female sex organs on same plant. So Anthoceros is homothallic plant. Male sex organs are antheridia and female sex organs are archegonia. Antheridia are developed first on thallu, this condition is called protandrous.Antheridia develop on dorsal side of gametophyte. Special chambers called antheridial chambers are produced on the surface of gametophyte. In each antheridial chambers single or up to 20 antheridia may develop. Each antheridium contains a stalk and ovoid body. Whole antheridium is covered by jacket cells. Inside antheridia, anthorozoids develop by mitosis.Archegonia are embedded in tissue of gametophyte. It does not contain any jacket cells around it, however its upper surface is covered by cover cells. Archegonium contain a swollen portion called ventre and long portion called neck. Neck contains neck canal cells, and ventre contain ventre canal cells and an egg.

Fertilization:

Antherozoids are attracted towards the archegonia chemotactically. The chemical for this movement oozes out by the bursting of neck and ventre canals cells. Antherozoids move into the archegonia and fertilize the egg. Resulting in the formation of zygote. Zygote changes into embryo.Sporophyte:Embryo develops into sporophyte. Sporophyte is diploid generation in life cycle of Anthoceros. Sporophyte of Anthoceros differs from other bryophytes in respect to its semi-dependence on gametophyte. It has chlorophyll in its epidermis to carry out photosynthesis.

Epidermis also contains stomata for exchange of gases. This feature makes it able to become independent from gametophyte in later stages of its growth. Sporophyte of Anthoceros does not contain well developed seta. The developed structures are foot and long capsule (sporogonium) with calyptra. Capsule contain columella in center and sides of columella has spores. Outer to this spore containing region is well developed and thick wall of capsule which carry out photosynthetic activity. The junction of capsule of and foot has meristematic tissue. This tissue adds new cells throughout the life of sporophyte. This feature resemble the sporophyte of flowering plants, in having the indeterminate growth due to presence of meristem.Spores inside the spore chamber are produced by meiosis. These haploid spores are dispersed after release from sporogonium. On falling at suitable place, spores germinate and produce new thallus.