Division : Bryophyta (Bryon = moss; phyton = plant)
The Bryophytes are mostly terrestrial plants which depends on external water for fertilization and completion of their life cycle. Hence they are called 'amphibious plants'. They include approximately 960 genera and about 24,000 species.
The Bryophytes generally grow in shady and moist places such as moist walls, damp rocks, moist soil and on decaying logs. They show either thalloid or leafy plant body.
In Bryophytes true roots are absent but rhizoids are present. Rhizoids are unicellular in liverworts while multicellular in mosses. They absorb water and minerals and also help in fixation of thallus to the substratum.
The vascular tissues are present. However, a conducting strand of few thick-walled cells is present in mosses.
The Bryophytes show heteromorphic alternation of generations in which the gametophyte is the dominant, green, haploid and independent phase while sporophyte is diploid recessive and partially dependent on gametophyte.
Bryophytes reproduce by vegetative means i.e. by special structures like tubers and gemmae while asexual reproduction takes by spore formation. Sexual reproduction occurs by formation of gametes.
The bryophytes are divided into two groups- liverworts and mosses.
Liverworts (Hepaticae) :
These are lower members of Bryophyta which process prostrate plant body. They are found in moist shady places. The thallus is dorsiventral, prostrate and with unicellular rhizoids. Some liverworts have stem-like axis and leaf-like appendages. (foliose liverworts).
They reproduce vegetatively either by fragmentation or by formation of small. green, cup like buds called gemmae. Each gemma develops into a young plant on detachment. Sexual reproduction occurs by formation of male and female sex organs borne on the same or different plants. After fertilization, there is formation of a diploid sporophyte i.e. sporogonium. It contains haploid spores produced by meiosis which on germination produce haploid young plants or gametophytes.
Examples :- Riccia, Marchantia. etc.
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| Riccia |
Mosses (Musci) :
These are higher members of Bryophyta which possess erect plant body. The gametophytic phase of the life cycle includes two stages namely protonema stage and leafy stage. The protonema is prostrate, green, branched and filamentous. (It is also called juvenile gametophyte). It bears many buds and the leafy stage is produced form each bud. Thus protonema helps in vegetative propogation. The leafy stage has erect, slender main axis and a branch (stem-like) bearing spiral leaf-like structures. It is fixed in soil by multicellular branched rhizoids.
during sexual reproduction, antheridia and archegonia are produced as sex organs in clusters at the tips of stem-like axis. The clusters of sex organs are concealed by a whorl of leafy appendages. The zygote gives rise to a well developed sporophyte with foot, seta and capsule. The haploid spores formed by meiosis are released by dehiscence of capsule.
Example :- Funaria, Polytrichum, etc.
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| Funaria |