What are Bryophytes
Bryophytes are known to be the oldest land plants. They are generally found in moist and shady regions.
Though they grow on land but are dependent on water for the sexual mode of reproduction due to which they are also known as amphibians of the plant kingdom. The body of bryophytes is haploid and comprises thallus and rhizoids for attachment to the substratum. True stems and roots are absent in the case of bryophytes.
Reproduction in bryophytes
The plant body of bryophytes produces gametes, hence gametophytes. The male sex organ is multicellular and called antheridium which produces antherozoids. The female sex organ is flask-shaped called archegonium which produces a single egg. Antherozoids are released in water where they fuse with eggs produced by archegonium resulting in zygote formation.
Zygote produces sporophyte which is a multicellular stage. The sporophyte is attached to the gametophyte as they depend upon the gametophyte for nutrition. This sporophyte produces haploid spores which germinate to produce gametophyte.
Importance of bryophytes
1. Mosses are used as food for many animals.
2. Peat of sphagnum species is used as fuel.
3. Mosses and lichens decompose rocks to help to grow higher plants.
4. Mosses reduce soil erosion.
Bryophytes are subdivided into two major classes liverworts and mosses
Liverworts
Liverworts are generally found in shady regions such as the bark of trees, deep in woods, etc. The Thallus of this class is dorsiventral and well attached to the substrate. Certain members of this class possess tiny leaf-like appendages on stem-like structures e.g. Marchantia
Reproduction in liverworts is done by both asexual and sexual means.
Asexual reproduction
This kind of reproduction takes place through the formation of multicellular buds called gemmae on small receptacles known as gemma cups. Gemme on separating from the parent body results in new individual formation.
Sexual reproduction
This mode of reproduction results in spore formation from sporophytes by meiosis which germinates giving rise to free-living gametophytes.
Mosses
Mosses are flowerless plants that grow in shady regions. They are devoid of roots but have root-like rhizoids instead of attachments. The gametophytic stage of mosses consists of two stages namely the protonema stage and the leafy stage.
Protonema stage
The Protonema stage is a green, branched, filamentous stage and develops directly from the spore.
Leafy stage
Leafy stage as the bud develops from secondary protonema. They consist of a straight axis with spiral leaves. This stage also bears sex organs.
Sexual reproduction
Sexual reproduction involves antheridia and archegonia which are developed at the edge of shoots. Fertilization results in zygote formation which develops in the sporophyte. Mosses have elaborated sporophytes and complex spore disposable mechanisms than liverworts. Some examples are Funaria, Polytrichum, etc.