The term bryophyta is derived from two Greek words (Bryon: Moss; phyton: plant). Bryophytes are the simplest group of first land-inhabiting plants that tend to grow best in permanently moist conditions. They are not well adapted to live on land as they lack vascular tissue. It includes liverworts, hornworts and mosses. Bryophytes are commonly known as “Amphibians of Plant Kingdom” because they require external water for fertilization and completion of life cycle. Bryophytes include about 960 genera and 24000 species. They are worldwide in distribution on most parts of the earth wherever there is sufficient moisture to sustain plant life.
The characters of plants lying in Bryophyta are:
- Bryophytes mostly grow in moist and shady places. Some species are aquatic e.g. Riella, Ricciocarpus natans and Riccia fluitans. Polytrichum and some other species grow in xerophytic conditions.
- The gametophyte bearing the reproductive organs is independent and long lived, while the sporophyte bearing the spores is dependent on the gametophyte and is short lived.
- The gametophytic plant body may be thallose (not differentiated into stem and leaf) or foliose (differentiated into rhizoids, stem and leaves).
- The vascular tissues are absent. The plant body consists of simple parechymatous cells.
- The thalli of primitive forms remain attached to the substratum by unicellular smooth walled or tuberculate rhizoids. However, in higher forms, the rhizoids are branched and multicellular.
- In some bryophytes multicellular scales are present, which provide protection to the growing point. For example, Riccia, Marchantia.
- Reproduction is brought about by vegetative and sexual means.
- Water is essential at the time of fertilization.
- The sporophyte of Riccia is very simple; consists of capsule only, whereas in other bryophytes it consists of foot, seta and capsule.
- The capsule contains sporogenous tissues which divide meiotically to form four haploid spores.
- Spore is the first cell of gametophytic generation, which on germination gives rise to gametophytic plant body.
- The life cycle of a bryophyte shows regular alternation of gametophytic and sporophytic generation.