SUB CLASS SPHAGNOBRYA
ORDER SPHAGNALES
Sphagnum is an aquatic species . Sphagnum grows in water or marshy land , yet it shows xerophytic characters . But physiologically Sphagnum is hydrophyte . Sphagnum is also called peat moss or bog moss . They produce certain acidic substances which render the medium unsuitable for growth of pathogens . This slows down the decaying process of plant parts . Thus partially decomposed material accumulates at the bottom of water body , year after year .This material is compact , dark and is called peat . Hence the name peat moss is given to these plants .
Sphagnum has economic importance . It has remarkable water holding capacity , hence it is used in packing live plant parts for transportation . Sphagnum has some antiseptic properties ( used in Word War I ) . Sphagnum has great role in plant succession .
Gametophyte is differentiated into axis and leaves . Many small branches of limited growth are present at the apex of main axis , form a compact head called coma . Sphagnum has two types of branches - pendent branches ( turn downwards ) and divergent branches ( directed outwards and upwards ) . Leaves are arranged in spiral phyllotaxy on main axis and lateral branches .
Remarkable water holding capacity of sphagnum is due to retort cells and hyaline cells . Cortex of main axis has bottle or retort cells . They accumulate water . Mature leaves have chlorophyllous cells as well as hyaline cells ( capillary cells ) . Hyaline cells have spiral thickenings and water holding capacity .
Vegetative reproduction in sphagnum occurs by special branches called innovations . In sphagnum one branch at each node develops more strongly than others , it is called innovations . Antheridia develop on small catkin like branches and archegonia develop on short bud like branches . Sporophyte of Sphagnum is made up of foot , seta and capsule . The foot is bulbous / cylindrical and haustorial in nature . Elongated , leafless axis of archegonial branch , present at the base of sporophyte is called pseudopodium . Pseudopodium elevates the sporophyte . Sphagnum capsule dehisces by explosive air gun mechanism . It is due to pressure developed by air space below the spore sac .
Since sphagnum shares many features with hepaticopsida , anthocerotopsida and bryopsida , it is regarded as synthetic group .