Bryophytes are amphibians of plant kingdom as they complete their life cycle in both water and on land. These mainly grow in damp, shady places, especially in the hills.
Features of Bryophytes
- They are embryophytes that do not have vascular tissues (neither xylem nor phloem), where multicellular sporophytes are always borne on the gametophytes.
- No true leaves and roots, as their independent plant body is gametophytic (haploid).
- Sex organs are jacketed as they are always surrounded by one or several layers of sterile cells.
The bryophytes are pioneers of vegetation. They are the first ones to grow on various habitats like rock, lava, sand, water and act as soil binders.
The mosses hold water better than the soil thus improve the microhabitat for seeds of other plants to grow.
These are the sources of food for fish and birds and their dried plant body is used as nesting materials by birds.
There are three main types of bryophytes:
- Flat, ribbon-like - Liverworts (Marchantia)
- Small, leafy plant body - Mosses (Funaria)
- Flat, thalloid plant body bearing a horn-like sporophyte - Hornworts or Anthoceros
In all types of bryophytes, the main plant body is gametophyte, larger and more persistent and photosynthetically active which bears the sex organs. In mosses, the gametophytic plant body is a leafy stem called gametophore but in liverworts and hornworts the plant body is usually a thallus, that is ribbon-like or heart-shaped and bilaterally symmetrical.
The body is without roots, stems and leaves. The plants are anchored to soil by rhizoids, which are unicellular in liverworts and hornworts and multicellullar in mosses. Rhizoids help in anchorage and also in absorption of water and minerals from the substratum.
The male sex organs are antheridia and female sex organs are archegonia. The gametes are produced in the sex organs. Male and female gametes fuse to give rise to a zygote which develops into a sporophyte. Sporophyte remains attached to gametophyte and depends on it for food and minerals. The sporogenous tissue in the sporophyte undergoes meiosis to produce haploid spores. The spores, on dispersal, germinate to give rise to a gametophyte again.
In all three types of bryophytes, the life cycle shows Alternation of generations.
- Gametophyte (undergoes Mitosis): Gamete producing phase of plants
- Sporophyte (undergoes Meiosis): Spore producing phase of plants