Bryophytes Introductory Lecture PDF

# Bryophytes The term Bryophyta (Gr. bryon=moss + phyton=plant) is applied to a group of plants in which the plant body is simple, flat thallus still in the process of developing, resembling to some of thallophyta in vegetative structure, but showing an advance in the method of reproduction. The s...

# Bryophytes The term Bryophyta (Gr. bryon=moss + phyton=plant) is applied to a group of plants in which the plant body is simple, flat thallus still in the process of developing, resembling to some of thallophyta in vegetative structure, but showing an advance in the method of reproduction. The sex organs are multicellular, and each sex organ is protected by an outer wall of sterile cells surrounding sex cells. They exhibit distinct heteromorphic alternation of generations. The principal phase is gametophyte. It is conspicuous and nutritionally independent. The sporophyte is simple and comprises of foot, seta and capsule. It never becomes independent, but remains attached to the gametophyte throughout its life. ## General Account of Bryophytes ### Habitat About 960 genera and 24,000 species of bryophytes exist in the universe. They range from few mm to 30 cm or more in size. With the exception of few aquatic forms, they are truly land plants. They are found in humid and shady places. The bryophytes are abundant in moist mountain forests of tropical and sub-tropical regions. Species like Riccia, Marchantia, Anthoceros and Funaria are common in the plains. Water is required at the time of fertilization, therefore they are commonly called amphibians of the plant kingdom. ### Plant Body The gametophyte is haploid (n) and an independent plant at maturity. In many cases the gametophyte is a thallus, i.e., plant body is without differentiation into root, stem and leaf, for example in Marchantia and Anthoceros. In others it is externally differentiated into stem and leaves, however there are no roots. The absorbing organs are rhizoids. The sporophyte is diploid (2n) and dependent upon gametophyte for its nutrition and remains attached to the gametophyte. It consists of foot, embedded in the gametophyte and absorbs nutrition from it, seta which raises the sporophyte above the level of gametophyte, and conducts food absorbed by the foot, and capsule, the spore-producing structure. The sporophyte of the bryophytes is generally called a sporogonium. ### Reproduction The bryophytes reproduce by vegetative, sexual and asexual modes of reproduction. The gametophyte reproduces sexually by formation of gametes, whereas the sporophyte reproduces by formation of spores, therefore the mode of reproduction is asexual. #### Vegetative Propagation In some species asexual reproduction takes place by the vegetative methods of fragmentation and gemmae. However, asexual spores like endospores or akinetes produced in algae are absent. #### Sexual Reproduction (gametes) The sexual reproduction is oogamous type. The gametes are produced in multicellular sex organs. The male gametes are small and motile, while the female gametes are large and non-motile. The sex organs are antheridia and archegonia. These are multicellular, and each sex organ is protected by an outer wall of sterile cells surrounding sex cells. Both kind of sex organs may develop on the same plant (monoeious or homothallic) or on different plants (dioecious or heterothallic). Each antheridium is usually club-shaped. It contains androcytes or antherozoid mother cells surrounded by a single layer of sterile jacket cells. Each androcyte metamorphoses into a motile biflagellate antherozoid or male sperms. The archegonia are usually flask-shaped. Each archegonium consists of a basal swollen portion, the venter, and an elongated part, the neck. An axial row of few neck canal cells, a ventral canal cell and an egg or oosphere. #### Fertilization Water is essential for fertilization. The jacket of mature antheridium ruptures liberating the sperms. The motile flagellated sperms swim in the film of water and reach the neck of an archegonium. In the meantime axial row of neck canal cells disorganize and the tip of the archegonium ruptures opens. The antherozoids enter the neck and swim down to the egg. One of these sperms fertilizes the egg to produce zygote without delay. The wall of venter enlarges alongwith the developing embryo to form a protective, multicellular envelope, the calyptra. The zygote undergoes repeated divisions to form an undifferentiated, multicellular structure, the embryo. The first division of the zygote is transverse and the apex of the embryo develops from the outer cells. The cells of embryo undergo differentiation to produce a sporogonium representing the sporophyte. #### Asexual Reproduction (spores) => Sporophyte A mature sporogonium consists of a basal swollen foot, a stalk or seta, and a spore-producing structure, the capsule. The capsule comprises of sporogenous cells surrounded by a layers of sterile cells. These cells undergo divisions repeatedly and last generation of cells is called spore mother cells which undergo meiosis to produce tetrads of haploid spores. The spores are non-motile, cutinized, wind-disseminated and alike, therefore the bryophytes are homosporous. In most cases, e.g., in Riccia and Marchantia, sterile cells called elators are also produced alongwith spores. #### Germination of Spores Each spore upon falling on a suitable place germinates to a gametophyte plant directly or into a filamentous or thalloid green protonema which give rise to the thallus (gametophyte). ## Alternation of Generations The life cycle of bryophytes exhibit alternation of generations. There is an independent; haploid, gamete-producing generation, the gameotphyte. It bears sex organs, the antheridia and archegonia, in which male and female gametes are produced. Fertilization requires water and the resultant zygote develops into an embryo that matures into diploid, dependent, spore-producing structure, the sporogonium (sporophyle). The sporogonium remains attached to the gametophyte and draws nutrition from it. It is differentiated into foot, seta and capsule. The capsule contain spore-producing cells that undergo meiosis to produce tetrad of meiospores. The spores upon germination produce an independent gametophyte plant. ## Affinities of Bryophytes The hypothesis did not claim that water ferns after adapting aquatic mode of life have retained their vascular system. # Economic and Ecological Importance of Bryophytes Although about 24,000 species of bryophytes exist, but none of these is of direct use to man except the peat moss (Sphagnum), hair cap moss (Polytrichum) and some liverworts (Marchantia). However, they influence man through their role as rock builders, in soil conservation, etc. Some important direct and indirect economic and ecological importance of bryophytes is as under: ### i. Bryophytes and Peat Formation Peat is a brown or dark coloured spongy matter produced as a result of partial decay of dead organic matter in the bog, and due to compression and carbonization under pressure by the overlapping deposits and water. Sphagnum and other mosses are chief component of the peat. The peat is rich in carbon, therefore used as fuel in generating power, in making illuminating gas, in preparation of ethyl alcohol, etc. It is also used in horticulture. It is added to the clayey and sandy soils to improve their texture. Since peat can retain moisture it is used to as packing material for shipment of live plants, vegetables, perishable fruits, etc. ### ii. Role in Soil Conservation Since bryophytes grow in dense stands forming a mat, they prevent soil erosion. The intertwined moss stems and underground rhizoids bind the soil particles firmly. They can hold large amount of water and reduce the run off. ### iii. Role in Soil Development The mosses alongwith lichens play an important role in soil development on the surface of a bare rock. The lichens are pioneers and they are replaced by mosses during succession. The mosses can retain moisture and form humus to build the substratum. Most herbs germinate among these mosses ### iv. Role as Rock Builders Bryophytes such as Bryum, Hypnum, Fissidens, etc growing in association with other aquatic plants like chara play a remarkable role as rock builders. These plants grow in waters rich in calcium bicarbonate. They decompose, releasing carbon dioxide. The insoluble calcium carbonate precipitatum hardens and form lime rocks ### v. Role as Pollution Indicators It has been demonstrated that both alive and air dried mosses particularly Sphagnum can absorb metals. Because of this property they are used as atmospheric and aquatic pollution indicators, and in mineralogical surveys ### vi. Medicinal Use of Bryophytes Marchantia polymorpha, Anthoceros, Riccia and Polytrichum spp are reported to have medicinal properties. They are used as antitumor, to cure pulmonary tuberculosis and afflictions of the liver. Similarly Polytrichum commune is used to dissolve stones of kidney and gall bladder. A distillate of peat tar called sphagnol is used in treatment of skin disease. The Sphagnum is used for making absorbent bandages in treatment of boils and discharging wounds. ### vii. Bryophytes as Source of Antibiotics In recent years it has been reported that bryophytes are antibiotically active. Conocephalum conicum, Dumortiara hirsuta and Sphagnum strictum have been tested for their antibiotic activities. The first two have been reported to inhibit the growth of Candida albicans. The Sphagnum spp inhibit the growth of Staphyloccous aureus. Uptil now about 52 species of bryophytes belonging to 40 genera have been tested for their antibiotic activities and found to inhibit growth of 18 bacterial genera such as Sarcina lutea, Bacillus subtilis, Escherichia coli, Salmonella typhi, Vibrio cholerae, etc; and 3 fungal genera Aspergillus niger, Curvularia lunata and Hemithosporium oryzae. ### viii. Bryophytes as Experimental Tools The liverworts and mosses are used as experimental tools in various disciplines of botany such as genetics, experimental morphology and physiology. Polyploidy had been studied in bryophytes. ### ix. Bryophytes as Source of Food Bryophytes are not directly used as food, however some species of bryophytes are used in manufacture of different kinds of food. Brym and Polytrichum capsules are used in chick food. The Sphagnum is used as a famine food in China.