Bryopsida are also known as mosses and are the higher bryophytes which comprise of almost 15,000 species placed under 600 genera.
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Habit and Habitat of Mosses
Mosses occur in almost all situations where life is possible. The plant body is better adapted to life on land than the thallus of liverworts. Different species grows in diverse habitats. Few species such as Fontinalis antipyretica are aquatic. A few species such as Sphagnum grow in bogs. Many species grows in soil, rocks, buildings, tree trunks etc.
Morphology of Mosses
The plant body is a gametophyte that grows either erect or prostrate with little or no branching. The moss gametophyte phase comprises two growth stages, namely the juvenile stage also called as protonema and the adult leafy stage.
- Protonema– It is green, creepy, branched and filamentous structure with no sex organs.
- Leafy stage– It consists of upright slender axis bearing spirally arranged leaves. This stage produces sex organs. The three fundamental organs of the moss plant are stem, leaves and branches.
- Stem- It may be branched or unbranched. All the branches maybe erect or some may be prostrate. Dichotomous branching is not seen. The branch arises from below the leaf and is not axillary.
- Leaves- The leaves are arranged spirally on the stem. In some cases, leaves have single midrib and in some species, leaves have no midrib. In form they present a great variety ranging from narrowly linear to oblong ovate or broadly sub orbicular. The leaf cells contain large and prominent chloroplasts.
- Rhizoids- In mosses, the rhizoids are branched and multicellular with oblique septa between the cells. The main rhizoidal strands are conducting and anchoring in function. They grow vertically and from these finer branches arise which grow obliquely. The secondary lateral bears fine tertiary branches.
Distinctive Features of Mosses
- The plant body is radially symmetrical and differentiated into stem, rhizoids and leaves.
- The stem shows certain tissue differentiation like cortex and traces of vascular bundles.
- The gametophyte has two stages- protonema and the leafy stage.
- Most of the mosses consist of leaves with a midrib.
- The rhizoids are multicellular with oblique septa.
- The sex organs have longer stalks as compared to other bryophytes.
- Sporophyte is more elaborate and complex in nature. No presence of elaters.
- Peristome teeth and operculum are present in capsule of most of the genus.
Reproduction in Mosses
Asexual Reproduction
The capacity for vegetative reproduction is widespread in the mosses. The types of asexual reproduction seen in mosses are as follows:
- Progressive growth and death: In some genera of mosses like Polytrichum, they possess a creepy main stem bearing upright branches. The older portion of creeping stem decay which leads to separation of upright stem. It increases the number of leafy gametophytes.
- Branching of leafy stem: In many mosses, the leafy axis develops buds at the base which later grows into branches and get detached by the decay of basal connecting parts. Each detached branch give rise to new individuals.
- Formation of stolons: Some mosses develop stoloniferous branches from the base of the stem. The stolons may be naked or bear small scaly leaves and creep on beneath the soil. Eventually tip of each stolon gives rise to new individuals.
- Separation of a specially modified branch of bud-like form: In some species of Bryum, the detached structure which functions as an organ of vegetative propagation is a modified branch of bud-like form.
- Preliminary protonemal stage: Moss plants arise as lateral buds from the extensively branched primary protonema. The protonema originating from single spore may possess several buds that later develops into leafy shoots. The connecting portions of protonema decays which results in the separation of leafy shoots as different individuals.
- Secondary protonema: The mosses have great power of regeneration. Any undamaged cell of a detached or injured portion under suitable conditions develops into a filamentous structure which is known as secondary protonema. The most common example is Sphagnum.
- Tubers: In mosses, small underground resting buds are formed which are known as tubers. They are usually formed on stems, leavers and rhizoids and remains inactive during unfavourable condition. On germination, each tuber produces protonema which later grows to leafy plant. Examples are Bryum, Pottia etc.
- Gemmae: Green, oval bud like structures are produced on short stalks of many mosses. These are called gemmae. Each gemma gives rise to protonema. They are produced in different parts of stem and may also differ in structure in different genera. Gemmae formation is seen in species like Bryum coronatum, Grimmia etc.
- Persistent apices: In some species, with the creeping stems the entire plant dries up in the dry season except the growing apices. The cells of surviving apices secrete a mucilage sheath around them and persist. With the return of favourable conditions the surviving apices resume growth.
- Apospory: The formation of gametophytes directly from the cells of the sporophyte other than the sporophyte other than the spore is called apospory. The apospory produced moss plants have a diploid chromosome number.
Lifecycle of a Moss Video
Sexual Reproduction
Position of sex organs– The sex-organs containing the gametes are borne in clusters in mosses. Some mosses are monoecious and some are dioecious. On the basis of distribution of sex organs, the monoecious mosses are kept under following categories-
- Paroicous mosses: In some monoecious plants, the sex organs are borne in the same head in separate groups. The antheridial and archegonial groups in the same head are demarcated from one another by one or two perichateal bracts. Such monoecious mosses are called paroicous mosses.
- Autoicous mosses: The monoecious mosses in which the two kinds of sex organs are borne on separate branches of the same plant are called autocious mosses.
- Synoicous mosses: The antheridia and archegonia occur in the same head intermingled with each other.
Antheridia: The antheridium is club-shaped in structure supported by a stalk. All mosses have the same antheridial structure but vary in size. The mature antheridium consists of mass of androcytes (Sperms) enclosed by a jacket layer of cells. The jacket layer at the apex of antheridium is differentiated into lid like structure.
Archegonia: Each archegonium consists of neck canal cells, a ventral canal cells and egg. The moss archegonia are similar to those of liverworts except that the moss archegonium has longer stalk, longer neck and a massive venter.
Fertilization: Water is needed for fertilization. In the mature archegonium, the neck canal and the ventral canal cells disorganize to form slimy mass that contains chemicals for sperm attraction. The biflagellate sperm swim down the canal and fuses with egg to form zygote and then sporophyte generation begins.
Sporophyte: The mature sporophyte is formed after the growth and development of embryo. It is differentiated into three parts namely-
- Foot- It forms the basal region and functions as attaching and absorbing organ. The region of contact between foot and thallus tissue is called placenta.
- Seta- It is a long slender structure which raises the capsule far above the gametophyte enabling ready dispersal of spores by wind.
- Capsule- In mosses, it is complex in structure and differentiated into three regions: apophysis region, middle or theca region, and the lid (operculum). Most of the mosses contain teeth-like projections in their capsule which are called peristome teeth. The apophysis region is responsible for photosynthesis.
Classification of Mosses
Smith divided the class Bryopsida into three sub-classes:
- Sphagnobora
- Andreabora
- Eubrya
Reimers in 1954 divided the class into five sub-classes:
- Sphagnidae- comprising of single order Sphagnales.
- Andreaeidae- comprising of single order Andreales.
- Bryidae- comprising of twelve orders.
- Buxbaumidae- comprising of single order Buxbaumiales.
- Polytrichidae- comprising of two orders- Polytrichales and Dawsoniales.
Buck and Goffinet divided Bryophyta (all mosses except liverworts and hornworts) into five classes:
- Takakiopsida
- Sphagnopsida
- Andreaeopsida
- Andreaeobryopsida
- Polytrychopsida
Economic Importance of Mosses
Ecological Benefits
Mosses, such as Sphagnum and Racomitrium lanuginosum, play a crucial role in ecosystems by stabilizing soil, preventing erosion, and aiding in soil formation. They have a remarkable capacity for water retention, which helps maintain moisture levels in forests and wetlands, ensuring the health of these habitats.
Additionally, mosses are significant in carbon sequestration, particularly Sphagnum species in peat lands, which store vast amounts of carbon and help mitigate climate change.
As bio indicators, mosses like Pleurozium schreberi are sensitive to environmental changes and pollution, making them valuable for monitoring air and water quality.
Commercial and Horticultural Uses
Mosses have several commercial applications, notably in horticulture and gardening. Sphagnum peat moss is a popular soil conditioner, improving soil structure, aeration, and moisture retention, which is essential for plant growth.
Mosses like Hypnum are also used decoratively in landscaping, terrariums, and bonsai due to their aesthetic appeal.
In the peat industry, Sphagnum peat has historically been used as a fuel source and continues to be valued as a soil amendment.
Furthermore, Sphagnum moss serves as an effective packing material for shipping live plants, flowers, and bulbs, thanks to its excellent moisture retention properties.
Environmental and Scientific Applications
Mosses serve as important environmental indicators and are used extensively in scientific research.
Species like Pleurozium schreberi are employed as bioindicators to monitor air and water quality, detect pollution levels, and assess the impact of acid rain and heavy metal deposition. In scientific research, Physcomitrella patens is a valuable model organism in plant biology and genetics due to its simple structure and ease of genetic manipulation. Additionally, mosses have potential medical applications; Sphagnum moss, known for its antibacterial properties, has been used traditionally for wound care and is being explored for modern medical uses.
Video on All about Mosses
References
- The Editors of Encyclopaedia Britannica. (2024, May 15). Moss | Definition, Characteristics, Species, Types, & Facts. Encyclopedia Britannica. https://www.britannica.com/plant/moss-plant
- Buck and Gaffinet. 2000. Bryophyte Biology Cambridgde University Press, Cambridge.
- Smith, G.M. 1955. Cryptogamic Botany. Vol. II. Bryophytes and Pteridophytes. Edi. 2, New York.
- Tansley, A.G. and E. Chick. 1901. Notes on the conducting tissue system in Bryophyta. Ann. Bot., 15 : 1-38.
- Campbell, D.H. 1925. The structure and development of mosses and ferns, New York.
- Bryophyte by B.R. Vashishta, A.K. Sinha, Adarsh Kumar (S.Chand & Company ltd)
- Vaisay, J.R. 1888. On the anatomy and development of the sporogonium of the mosses. J. Linn. Soc. Bot., 24 : 262-285.
- Parihar. N.S. 1967. An introduction to Embryophyta. Vol. I. Central Book Depot. Allahabad.
- File:Asexual reproduction moss svg diagram EN.svg – Wikimedia Commons. (2020, October 29). https://commons.wikimedia.org/wiki/File:Asexual_reproduction_moss_svg_diagram_EN.svg
- Hait, G., Bhattacharya, K., & Ghosh, A. K. (2012). A textbook of Botany, Volume I.
- Mitra, J. N., Mitra, D., & Choudhuri, S. K. (2010). Studies in Botany, Volume I.