Bryophytes are a group of small, non-vascular land plants. The term Bryophyta was first introduced by Braun in 1864. He included algae, fungi, lichens, and mosses in this group. Later, algae, fungi, and lichens were placed in a separate division called Thallophyta, and liverworts and mosses were placed in the division Bryophyta. The rank of division Bryophyta was first given by Schimper (1879).
Bryophytes Classification
According to the latest classification, Bryophyta is divided into three classes:
- Hepaticopsida (Liverworts)
- Anthocerotopsida (Hornworts)
- Bryopsida (Mosses)
The outline of the classification is given below:
Class 1. Hepaticopsida
- Order 1. Marchantiales (e.g., Riccia)
- Order 2. Sphaerocarpales (e.g., Sphaerocarpos)
- Order 3. Calobryales (e.g., Calobryum)
- Order 4. Jungermanniales (e.g., Pellia)
Class 2. Anthocerotopsida
- Order 1. Anthocerotales (e.g., Anthoceros)
Class 3. Bryopsida
- Order 1. Bryales (e.g., Funaria)
- Order 2. Andreales (e.g., Andreaea)
- Order 3. Sphagnales (e.g., Sphagnum)
- Order 4. Polytrichales (e.g., Polytrichum)
- Order 5. Buxbaumiales (e.g., Diphyscium)
Characters of three classes of bryophytes, i.e., Hepaticopsida, Anthocerotopsida, and Bryopsida, are given below:
Hepaticopsida (Liverworts)
- This class comprises approximately 280 genera and 9500 species.
- The name of this class is derived from a Latin word, Hepatica, which means liver. Hence, members of Hepaticopsida are referred to as liverworts.
- The plant body is gametophytic. The gametophyte may be thalloid (flat, strap-like) or foliose (leaf-like).
- The thalloid forms are prostrate, dichotomously branched, dorsiventral, and lobed.
- While in the foliose forms, leaves are entire, lobed, or divided and without midrib. Leaves arranged in two to three rows on the axis.
- Rhizoids are present in the plant body. They are unicellular and branched.
- Photosynthetic cells contain numerous chloroplasts.
- Pyrenoids are absent in chloroplasts.
- Members of this class can be either monoecious or dioecious.
- Sex organs are borne dorsally or apically, superficial or embedded in gametophytic tissue.
- Sporophyte is simple or represented by a capsule only (e.g., Riccia) or may be differentiated into a foot, seta, and capsule (e.g., Marchantia).
- Archesporium is endothecial in origin.
- Sporogenous tissue either forms only spores (e.g., Riccia) or is differentiated into sterile elater mother cells and fertile spore mother cells (e.g., Pellia).
- Elaters are unicellular and hygroscopic with spiral thickenings.
- The wall of the capsule lacks stomata and is one to several layers thick.
- Columella is not present.
- Dehiscence of the capsule is irregular or in a definite number of valves
Anthocerotopsida (Hornworts)
- This class includes about 6 genera and 300 species.
- The plant body is gametophytic. It is flat, dorsiventral, thalloid, and variously lobed.
- The thallus does not show any internal tissue differentiation.
- Rhizoids are smooth-walled.
- Scales are absent.
- Air chambers or air pores are absent.
- Each cell consists of a single chloroplast.
- Chloroplasts contain one pyrenoid.
- Mucilage cavities open on the ventral surface by slime pores.
- Sex organs are embedded in the gametophytic tissue.
- Antheridia develop singly or in groups in closed cavities known as antheridial chambers.
- The sporophyte is differentiated into a foot, an intermediate zone or meristematic zone, and a capsule.
- The sporophyte can show indeterminate growth, i.e., it continues to grow indefinitely.
- Archesporium is amphithecial in origin.
- Sporogenous tissue forms both fertile spores and sterile elaters.
- Elaters do not have spiral thickenings and are called pseudo-elaters.
- The wall of the capsule is four to six layers thick, and the epidermis shows the stomata.
- Capsules mature from apex to base. They usually dehisce by two valves.
Bryopsida (Mosses)
- 1. It is the largest class in Bryophyta and is represented by about 700 genera and 14000 species.
- 2. The main plant body is gametophytic. It is differentiated into two stages: juvenile stage and leafy stage (i.e., gametophore).
- The juvenile stage is represented by green, filamentous branched structures known as protonema. It develops from the germination of the spore.
- The gametophores are erect leafy branches that develop on the protonema.
- Gametophore is differentiated into three parts: rhizoids, stems, and leaves.
- Leaves are unlobed with a midrib. They are arranged spirally in three to eight rows on the axis.
- Rhizoids are branched, filamentous, and multicellular, with oblique septa.
- The stem is differentiated into a central conducting strand enclosed by the cortex.
- Sex organs are borne apically in groups on the main axis.
- The sporophytes are differentiated into foot, seta, and capsule.
- The seta is elongated and rigid.
- Columella is generally present. It is endothecial in origin.
- Archesporium is differentiated only in spores.
- Elaters are not found.
- Dehiscence of the capsule takes place by separation of the operculum.
- The presence of peristome helps in the dispersal of spores.
