Bryophyta

Bryophyta

The term Bryophyta was first coined by Robert Brawn in 1864. Bryophytes are the simple and primitive group of the moist terrestrial plant. These members are commonly called amphibian plants because water is essential for fertilization. This group is placed between algae and Pteridophyta. Member of bryophyte represents about 25,000 species. 653 species are also found in Nepal. Bryophyta includes three different categories of plants i.e. liverworts, hornworts, and mosses.

General characteristics of Bryophyta

• Bryophytes are commonly found in moist, shady, damp and cool places such as moist rocks, moist walls, moist soil surface and wooden logs.
• In the primitive group of bryophytes, the vegetative plant body is green and leafy thallus is present. Type of thallus is prostrate, dorsoventrally flattened and dichotomously branched. But in the advanced member of bryophyte vegetative plant body is aerial, erect and differentiated into rhizoids, axis, and leaves.
• True rot is absent but for anchorage and absorption they bear unicellular or multicellular rhizoids.
• Conducting tissue or xylem and phloem are absent.
• They reproduce by vegetative and sexual methods. Vegetative multiplication is by fragmentation, tuber formation, adventitious branches, and gemma cup. Sexual reproduction is by monogamous type. The male reproductive organ is antheridium and female reproductive organ is archegonium.
• Male gametes are biflagellate and motile.
• Water is essential for fertilization.
• Reproductive organs are multicellular and jacketed.
• Fusion product of male and female gametes is a diploid zygote. It develops sporophyte.
• They show distinct alternation of generation and embryo stage is present.

Alternation of generation in Bryophyta

In the life cycle of bryophytes, gametophyte and sporophyte generation are regularly alternate with each other to complete life cycle. Such a phenomenon is called alternation of generation. Gametophyte phase is dominant, independent, autotrop[hic and haploid. It reproduces by male and female gamete formation. Fusion product of male and female gamete is a diploid zygote. A zygote is the mother cell of sporophyte generation. It develops sporophyte. Sporophyte phase is reduced, diploid and depend on the gametophyte. It reproduces by haploid spore formation. Germination of haploid spore again gives rise to young gametophyte.

Classification of Bryophyta

Bryophyta is divided into three classes on the basis of gametophytic, thallus and sporophytic generation. They are:

• Hepaticopsida
• Anthocerotopsia
• Bryopsida