General characters of Bryophytes:
1. DISTRIBUTION
Bryophyta is a group of the simplest and the most primitive, non-vascular land plants and includes about 24000 species in 960 genera.
2. HABITAT
They are terrestrial in habitat and usually grow in moist and shady places but require presence of water to complete their life cycle and therefore regarded as amphibians of plant kingdom. However a few grow under diverse habitats such as aquatic submerged (e.g. Riella, Riccia fluitans, Ricciocarpus natans); in bogs (e.g. Sphagnum); as epiphytes on tree trunks and branches (e.g. Dendroceros); in deserts (Tortule desertorum) and even as saprophytes (e.g. Cryphtothallus mirabilis).
3. GAMETOPHYTE
It is the most conspicuous, nutritionally independent phase of plant representing dominant haploid phase in the life cycle. It produces sex organs and concerns with the sexual reproduction.
(1) Morphology: Plant body is either a simple thalloid, growing prostrate on the ground and attached to the latter by delicate unicellular hair like outgrowths called rhizoids e.g. Marchantia, Riccia, Pellia; while in others it is like rootless leafy shoots e.g. Porella or erect leafy plants with stem like central axis, leaf like appendages and roots like rhizoids e.g. Funaria, Polytrichum.
(ii) Internal structure: The vascular tissue i.e. xylem and phloem is completely absent. However, in few mosses like xylem like hydroids and phloem like leptoids which conduct water and food respectively have been reported.
(iii) Nutrition: The plants are green, possess chloroplast and hence are autotrophic in their mode of nutrition. However, a few species are saprophytes and lead a heterotrophic mode of nutrition e.g. Cryptothallus mirobilis, a liverwort.
REPRODUCTION
Reproduction by asexual spores (meiospores) is completely absent in Bryophytes.
(1) Vegetative reproduction: It occurs by
fragmentation, adventitious branches, tubers, gemma cups etc. Sexual reproduction is highly oogamous and sex organs are jacketed.
(ii) Sex organs: Male reproductive organs
are stalked ellipsoidal or club shaped antheridia producing a mass of numerous biflagellate male gametes, the antherozoids. Female sex organs are flask shaped archegonia consisting of a upper slender elongated neck and lower sac like swollen part, the venter enclosing a large naked non-motile egg.
(iii) Fertilization: Water or moisture is essential for the movements of sperms to the archegonia, where they fertilize the egg to produce zygote (2n).
5. SPOROPHYTE
Diploid zygote is the pioneer structure of sporophyte phase. It develops into a diploid, nutritionally dependent sporophytic plant body called the sporogonium chiefly concerned with the production of spores.
(i) Sporogonium: The wall of the venter forms calyptra providing protection to the developing sporogonium. Mature sporogonium is differentiated into foot, seta, and capsule, however, foot and seta are absent in Riccia and seta e.g. Riccia, Marchantia or indirectly as lateral buds from protonema e.g. Funaria is absent in Anthoceros and Corsinia.
(ii) Capsule: Haploid spores are differentiated from the diploid spore mother cells by meiosis. Spores are morphologically similar in size and shape called homosporous. However, in Marchantia out of 4 spores produced from each spore mother cell; two produce male thalli and other two female thalli, showing functional or physiological heterospory.
(iii) Spore: It is the first cell of gametophytic generation which germinate to produce gametophyte directly e.g. Riccia, Marchantia or indirectly as lateral buds from protonema e.g. Funaria.