The Bryophyta (Gr. bryon-moss; phyton-plants) is represented by about 850 genera and more than 23000 species, which are cosmopolitan in their distribution. Important characteristic points of the bryophyta are as follows:
1. Occurrence:
Majority of the plants are terrestrial, except a few, which occur in aquatic surroundings like Riccia fluitans, Ricciocarpus natans, Riella and Sphagnum. They like to grow in moist shady places. Some are epiphytic, e.g., members of Jungermanniales, and even some members are saprophytes, e.g., Buxbaumia.
2. Plant Body:
Either thalloid, e.g., members of Hepaticae, or foliose, e.g., members of Musci. Plant body is gametophytic and green in colour.
3. Size:
It is variable from microscopic as in Zoopsis (Jungermanniales), to gigantic size up to 40cm. or even more as in Dawsonia.
4. Absorptive Organs:
These are fine thread like structures called rhizoids. Rhizoids are present in thalloid plants on their ventral surface, and in foliose plants on their lower side.
5. Leaves:
In foliose plants, the leaves are present. In Jungermanniales, leaves are arranged in 2 to 3 rows and there is no midrib, but in mosses leaves are arranged spirally and a distinct mid rib is present.
6. Axis:
Axis is present in Jungermanniales as well as in mosses. In Jungermanniales, it is homogenous structure but a conducting strand is present in mosses.
7. Vegetative Reproduction:
Various means of vegetative propagation are by progressive death and decay of older parts of the plants, or by adventitious branches, gemmae, tubers, bulbils, and sometimes also by protonema.
8. Sexual Reproduction:
It is oogamous type, and sex organs are antheridia and archegonia. Antheridia are club-shaped structures and produce many unicellular, uninucleate and biciliate antherozoids. Archegonia are flask-shaped structures, and each encloses a single non-motile egg.
9. Fertilization:
It takes place in the presence of water and its ultimate product is an oospore or zygote. Oospore is the first cell of sporophyte.
10. Sporophyte:
Sporophyte is always dependent on gametophyte. It is differentiated generally into foot, seta and capsule. There may also be variations (either foot or seta is absent, or both are absent as in Riccia).
Foot: Function of foof is absorption. It absorbs food material from gametophyte.
Seta: Function of seta is elongation.
Capsule: Function of capsule is spore-production.
In capsule, spore mother cells and sometimes elaters are also present, e.g., Marchantia.
11. Spores:
After reduction division in spore mother cell four spores are formed, which remain arranged tetrahedrally. AH the spores are alike (homosporous). They germinate into gametophytic plants.
12. Alternation of Generations:
This group exhibits best example of heteromorphic alternation of generations.