In this article we will discuss about the three divisions of bryophytes:- 1. Marchantiophyta 2. Anthocerotophyta 3. Bryophyta.
Phyllum (Division) I: Marchantiophyta:
1. Gametophytes are either flattened thalli or leafy shoots.
2. The flattened ribbon-like to leaf-like thallus of the thallose liverworts are either simple or structurally differentiated into a system of dorsal air chambers and ventral storage tissues.
3. The dorsal epidermis of the thallus is punctured with scattered pores that open into the air chambers.
4. In the leafy forms, the leaves are arranged on the stem in one ventral and two lateral rows or ranks.
5. The leaves are one cell layer thick throughout, never have a midvein and are usually divided into two or more parts called lobes.
6. The ventral leaves which actually lie against the substrate, are usually much smaller than the lateral leaves that are hidden by the stem.
7. Rhizoids are hyaline (colourless), unicellular and unbranched.
8. Liverworts synthesise a vast array of volatile oils, which they store in unique organelles called oil bodies. These compounds impart an often spicy aroma and seem to discourage animals from feeding on them.
9. Sporophytes develop completely, enclosed within gametophyte tissues until their capsules are ready to open.
10. The seta, which is initially, very short, consists of small thin-walled, hyaline cells, elongates its length up to 20 times its original dimensions just prior to spore release.
11. The rapid elongation of seta pushes the darkly pigmented capsule out of the gametophy- tic tissue.
12. With drying, the capsule opens by splitting into four segments or valves.
13. The spores are dispersed into the winds by the twisting motions of numerous intermixed sterile cells, called elaters.
14. The liverworts disperse the entire spore mass of a single capsule in just a few minutes.
15. Protonema is globose and forms a single bud (shoot).
Phyllum (Division) II: Anthocerotophyta:
1. Gametophytes are: simple, flat, lobed and unspecialised thalloid.
2. The thallus shows a uniform internal tissue organisation.
3. Colonies of symbiotic cyanobacterium, Nostoc fill small cavities that are scattered throughout the ventral part of the thallus. These colonies appear as scattered blue-green dots when the thallus is viewed from the top.
4. Hornworts differ from all other land plants in having only one large algae-like chloroplast (chloroplasts with pyrenoids) on each thallus cell.
5. Like liverworts, the rhizoids are hyaline unicellular, and unbranched.
6. Sporophytes are very strong and lasting for several weeks. Hornworts get their name from their long, horn-shaped sporophytes.
7. The sporophyte is differentiated into a long cylindrical capsule and a bulbous foot.
8. At the base of the sporangium, just above the foot, is a mitotically active meristem, which adds new cells to the spore-producing zone throughout the lifespan of the sporophyte.
9. The sporangium releases spores at its apex, at the same time the new spores are being produced by meiosis at its base.
10. With drying, the capsule opens by splitting into two segments or valves.
11. Release of spore takes place gradually over a long period of time, and the spores are mostly dispersed by water movement rather than by wind. Pseudoelaters perhaps take place in spore dispersal.
12. Like liverworts, the protonema of hornworts is globose and forms a single bud (shoot).
Phyllum (Division) III: Bryophyta:
1. The mature gametophyte is differentiated into an upright branched axis and spirally arranged leaves.
2. The stem is differentiated into a central strand of thick-walled water conducting cells, called hadroids, surrounded by a parenchymatous cortex and a thick- walled epidermis.
3. The leaves are simple small sessile and with a distinct midrib. The lamina is only one-cell layer thick.
4. The rhizoids are multicellular, branched and reddish-brown in colour.
5. The sporophyte is differentiated into foot, seta and capsule.
6. The seta tears the archegonial enclosure early in development, leaving the foot and base of the seta embedded in the gametophyte. The elongated seta raises the capsule much above the gametophyte.
7. The sporophytes are strong and long- lived, lasting several weeks.
8. With drying, the capsule breaks open at its tip. The peristome teeth are folded down into the spore mass and then bend outward, dispersing the spores into the drying winds.
9. The spores can travel long distances on wind.
10. In mosses, cell specialisation occurs within the protonema to form a horizontal reddish-brown anchoring filaments called caulonemal filaments and upright, green filament, called chloronemal filaments. Subsequently, some cells of the caulonemal filaments specialised to form leafy buds that will ultimately form the adult gametophytic shoots. So numerous shoots develop from each protonema.