Bryophytes
Bryophytes are non vascular land plants of moist habitat. They include about 960 genera and 24k species. The plant body of bryophyte is more differentiated than that of algae. These are the unique group of plants commonly regarded as 'amphibian of plant kingdom', intermediate between aquatic algae and terrestrial pteridophytes.
Characteristics of Bryophytes
1. They grows generally in large numbers on wet soils, edges of rocks, walls, tree trunks etc., especially during spring season.
2. The dominant phase in the lifecycle of bryophyte is gametophyte. It is a thallus, i.e., not differentiated into root, stem and leaves. In majority of bryophytes the plant body is simple, dorsiventrally differentiated dichotomously branched thallus made up of parenchymatous tissue. They possess many hair like structures called rhizoids which fix them to the substratum. They help in the absorption of water and minerals. The vascular tissues are absent, conduction of water and food takes place from cell to cell by diffusion.
3. Gametophyte produces multicellular sex organs, namely antheridia and archegonia. The antheridium produces large number of biflagellate male gametes called sperms. The archegonium is flask shaped with tubular neck and swollen venter containing a female gamete called egg. Presence of water is necessary for the fertilization.
4. Vegetative reproduction is quite common, which occurs through fragmentation, gemmae, tubers, and adventitious buds.
5. Sexual reproduction is oogamous type. After fertilization, the diploid zygote formed develops into a sporophyte, being supported and fed by gametophytic tissues. The sporophyte produces haploid spores through meiosis, which on germination produces gametophyte directly or through a juvenile filamentous stage called protonema, on moist places.
6. The lifecycle of a bryophyte exhibits two generations-gametophytic and sporophytic. The gametophytic generation consists of green, free living haploid thallus, the sex organs and the gametes. The sporophytic generation is short lived, diploid, multicellular sporophyte which is fixed and dependent upon the gametophyte for nutrition, support and shelter.
7. The gametophytic and sporophytic phases are morphologically and cytologically different regularly alternate to complete the lifecycle of bryophyte. Hence, bryophyte show alternation of generation.