The bryophyta are the first land habiting plants which includes 960 genera and 25,000 species. The plants belonging to Bryophyta are called bryophytes. The word ‘Bryophyta’ is derived from Greek word which means; bryon=moss and phyton=plant. The study of bryophytes is called bryology. Hertwig is consider as father of bryology. They are the first plant having heteromorphic alternation of generation in plant kingdom.
Characteristic of Bryophytes
Habitat: It is cosmopolitan in distribution and mainly found in moist and shady places. Some species are lithophyte (habiting on rocks), epiphytes or aquatic.
Morphology: The main plant body is gametophyte which is haploid. It is green thalloid in liverworts and hornworts. Thalloid (thallus) is differentiated into rhizoids, short stem and simple leaf like as in mosses.
Attachment: Plant remains attached to substratum with the help of rhizoids. Rhizoids may be unicellular or multicellular and also function in absorption of water and minerals for plant body.
Mode of Nutrition: Most of the bryophytes are autotrophs with a few species being saprophytes like buxbaumia aphylla.
Vascular Tissues: Both vascular tissues xylem and phloem are absent. So, It is also called as non-vascular cryptogams. Internally it consists of parenchymatous tissue which helps in transportation of water & minerals and translocation of food.
Alternation of Generation: Bryophytes show distinct alternation of generation for completion of their life cycle. It has independent gametophyte cycle and parasitic saprophyte cycle.
Vegetative Reproduction: It takes place by fragmentation, Gemma, protonema, adventitious branches and tubers.
Sexual Reproduction: It is of advanced oogamous type.
Sex Organs: Sex organs of bryophyte are multicellular covered in single layer of sterile jacket cells. Archegonia is the female sex organ having flask shaped structure. Antheridia is the male sex organ which are club shaped.
Structure of Sex Organs: The archegonium has tubular neck consisting of 4-10 neck canal cells enclosed in ventral rows of cells. In Marchantia 4-6 nek canal cells are present while in Fumaria 6-10 neck canal cells are present. It may be erect (Funaria) or inverted (Marchantia) and consists of central large egg cells.
Antheridia is stalked and surrounded by single layer of sterile jacket covering a mass of androcytes which give rise to antherozoids (in Marchantia).
Gametes: The antheridia produce numerous biflagellate motile male gametes or antherozoids. The flask shaped archegonium produces an egg or oosphere.
Fertilization: Male and female gametes are bought together with the help of water current and fuses to form zygote. Here water is necessary for fertilization and that’s why bryophytes are also called as amphibian of plant kingdom.
Development: Zygote divides mitotically rapidly resulting into multicellular embryo called as sporogonium. Sporogonium develops into sporophyte which completely (in Marchantia) or partially (in Faunaria) parasitic & depends on gametophyte for its whole life.
Bryophytes are homosporous i.e. all spores are of same kind and not differentiated into microspore and megaspore. Spores on germination give rise to gametophytic plant body.
Classification of Bryophytes
Bryophytes are classified into three classes on the basis of types of thallus (adapted by Braun).
- Hepaticopsida or Liverworts
- Anthocerotopsida or Hornworts
- Bryopsida or Musci
Hepaticopsida or Liverworts
Hepaticopsida is further divided into four orders.
Order 1: Marchantiales
It includes bryophytes like Riccia, Marchantia etc.
Order 2: Sphaerocarpales
Example: Sphaerocarpos
Order 3: Calobryales
Example: Calobryum
Order 4: Jungermanniales
Example: Pellia
Characteristic Features of Hepaticopsida
The important characteristic features of hepaticopsida are:
- It includes 280 genera and 9,500 species.
- Liver shaped plant body so, called as liverworts.
- Plant body is Gametophyte which is leafy, dorsoventrally flattened & dichotomously branched thallus.
- The ventral surface bears unicellular rhizoids and multicellular scales.
- The absorption of water and minerals is by rhizoids while scales help in fixation.
- The gametophytes is composed of simple tissues. The photosynthetic cells contain numerous chloroplasts without pyrenoids.
- Sex organs are developed from the epidermal cells located on the dorsal side of thallus except in some species where it is terminal in position.
- Sporophytes are simple and are differentiated into foot and capsule (e.g. Riccia) or foot, seta and capsule (in Marchantia). Capsule shows limited growth without having stomata or chlorophyll.
- Elater may be present which is diploid (2n). It is hygroscopic in nature and helps in spore dispersal.
- Sporophyte is completely parasite and depends on gametophytes.
- Pyrenoids present (but absent in Marchantia).
- Collumella is absent.
- Spore dispersal is irregular, assisted by elater and is hydrochasy type.
- Examples: Marchantia, Riccia, Porella, Pellia etc.
Anthocerotopsida or Hornworts
- It consists of only one order, Anthocerotales
- Characteristic Features of Anthocerotopsida
- It includes 300 species along with continuous discovery of new species.
- The gametophytes is small with horns like structure. So, called as hornworts.
- Gametophyte is dorsoventrally flattened, attached to substratum & dichotomously branched thallus.
- The ventral surface bears only unicellular rhizoids, scales are completely absent.
- The absorption of water and minerals is by rhizoids which also helps in fixation.
- The gametophytes is composed of homogenous tissues. Each cell of gametophyte (thallus) has a chloroplast, a nucleus and pyrenoid.
- Sex organs are antheridia which arise on the dorsal side of the thallus from hypodermal cells and archegonia remains sunk in the tissues of thallus on dorsal side which is developed from superficial cells.
- Sporophytes is elongated and cylindrical shaped with bulbous foot, an intercalary meristematic stem like and capsule.
- Elaters are absent, pseudo elaters help in spore dispersal.
- Sporophyte is partially parasitic depending on gametophytes.
- Pyrenoids usually present.
- Collumella is present.
- Spore dispersal is irregular, assisted by pseudo elater and is hydrochasy type.
- Examples: Anthoceros, Notothylas etc.
Bryopsida or Musci
Class bryopsida (musci) is further divided into five orders.
- Bryales
- Andriales
- Sphagnales
- Polytrichales
- Buxbaumiales
Characteristic Features of Bryopsida
- It is the largest class of Bryophyta including 1400 species and commonly called as mosses.
- The gametophytes is small with erect structure.
- Gametophyte is prostate, branched with erect gametophores.
- The ventral surface bears only multicellular oblique rhizoids without scales.
- The absorption of water and minerals is by rhizoids which also helps in fixation.
- The gametophytes is differentiated into outer thin walled cell, cortex and central conducting strand, medulla.
- Sex organs are epidermal in origin.
- Elaters and pseudo elaters both are absent instead, trabeculae is present.
- Sporophyte is partially parasitic depending on gametophytes.
- Pyrenoids are absent.
- Collumella is present.
- Spore dispersal is regular, assisted by peristome, annule etc.
- Examples: Funaria, Polytrichum, Sphagnum etc.
Examples of Bryophytes
Some common examples of bryophytes are: Marchantia, Riccia, Anthoceros, Funaria, Polytrichum, Sphagnum etc.
Importance of Bryophytes
Bryophytes are important in various ways. It contributes to economic, medicinal and research sectors. Some species are harmful also.
Economic Importance
Bryophytes grows as dense mats on the soil surface. It helps in soil conversation by preventing soil from sweeping out in erosion and flood.
Sphagnum, a peat moss is of highly economic value. The dark compact peat left after the decaying of sphagnum is used as fuel in horticulture. Sphagnum is also used for retaining water holding capacity of the soil in nursery.
They are the earlier inhibitors of rocks, barren field etc. Mosses along with lichens plays important role in formation of soil and initiating colonization by slowly decomposing rocks and barren fields into humus rich soil.
Lichens along with mosses are bioindicator of air pollution. The places with higher air pollution does not support growth of these species.
Medicinal Importance
Some bryophytes are used in preparation of antibiotics. Tea prepared from polytrichum commune is believed to dissolve kidney stone.
Sphagnum is used in surgical dressing and found superior to cotton dressing.
Herbal medicines made with bryophytes has been common in ancient China, India and native Americans for long time.
Some research has found that Polytrichum juniperinum has anticancer property.
Harmful Aspects of Bryophytes
According to van Wijk et al., 2003, Bryophytes creates a deep bed layer on the soil (canopy layer) which blocks the rain, wind and sunlight directly to the soil creating humid and swampy throughout the year. This is found to decrease little fall on ground vegetation.
It habitat on trees and its branches which may cause degradation of its bark and outer layers.
References
1. https://www.sciencedirect.com/science/article/pii/S1873965212000059
2. https://courses.lumenlearning.com/boundless-biology/chapter/bryophytes/
3. http://flora.huh.harvard.edu/FloraData/001/WebFiles/fna27/FNA27-1-Morphology.htm
4. http://tolweb.science.oregonstate.edu/Bryophyta/20599
