Bryophyta
General Characters, Classification, Reproduction And Affinities
Q.1. Give the introduction and characters of bryophyta.
Related Questions-
Q. Describe the characters of following class
(i) Hepaticopsida (ii) Anthocerotopsida (iii) Bryopsida. (2012)
Q. Explain the classification of bryophyta. (2008, 11)
Q. Write a brief outline of classification of Bryophytes with examples and their characteristics. (1995, 98)
Ans. The term Bryophyta was coined by Robert Braun in 1864.
The Bryophytes include the simplest and most primitive member of the Embryophyta. This include about 960 genera and 24,000 species. They occupy an important place in the plant kingdom although they have little economic value. They are cosmopolitan in distribution, mostly moist and shade loving but terrestrial. These plant occur in abundance in the temperature regions and are most common in rainy seasons. They usually grow in tufts or cushions and contribute much as a whole the green colour of mountains and forests.
With the exceptions of a few water forms, e.g. Riccia Fluitans, Ricciocarpus, Riellia, the Bryophytes are simplest and truly land inhabiting plants, present on moist and shady places. They may be regarded as incompletely adopted to land conditions, because they require water for vegetative growth, fertilization and other processes of life and hence are commonly called as “amphibians of plant kingdom”.
Characteristic Features of the Bryophytes: -
1. They usually occur on moist and shady places.
2. The plant body is green in colour and have no differentiation of true leaf, root and stem. This is either thalloid in appearance (liver worts) or may have a differentiation of ‘leaf’ stem and rhizoids (Musci).
3. The plant body is gametophyte.
4. Plant remain attached to the substratum by means of rhizoids, whose function is fixation and absorphtion. They may be unicellular or multicellular and smooth walled or tuberculated.
5. Internal structure of the thallus or plant body does not show any vascular tissue like xylem or pholem.
6. The gametophytic plant body reproduces both by vegetative and sexual means.
7. The sexual reproduction is of oogamous type and take place by definite male (Antheridium) and female (Archegonium) reproductive organs.
8. Antherozoids are motile, biciliated structure, produced in large numbers.
9. Archegonium is multicellular flask shaped organ having neck cancal cell, ventral canal cell and an egg.
10. Water medium is essential for fertilization.
11. Fusion of antherozoid and egg results in the formation of zygote or oospore which is diploid (sporophyte) in nature.
12. The oospore develops into the sporophyte which is usually differentiable into foot, seta and capsule.
13. Spores are formed in capsule after reduction division. All spores are alike.
14. Spores on germination give rise to the gametophytic plant body usually through protonema.
15. There is a distinct alternation of generation.
Classification of Bryophytes: - The name Bryophyta was first introduced by Braun (1864). but he included Algae, Fungi, lichens and mosses in it. Schimper (1879) gave Bryophyta the rank of a division. Eichler (1883) first of all recognised the following two classes in the division Bryophyta.
Following the international code of Botanical Nomenclature they called the class Hepaticae as Hepati-copsida, Anthocerotae as Anthocerotopsida and Musci as Bryopsida.
Proskauer’s classification is given below :
Class with Characters: -
I.Class : Hepaticopsida: -
1. The plant body are dorsiventrally flattened thalloid or faliose.
2. The plant body is prostrate lobed and dichotomously branched.
3. The ventral surface of the thallus bears many unicellular, unbranched, smooth walled, and tuberculate rhizoids and scales.
4. Photosynthetic cells always contain numerous chloroplasts without pyrenoids.
5. Sex organs develop from the superficial cells situated on the dorsal side thallus except in few cases where the sex organs are terminal.
6. The sporophytes are simple or may be represented by capsul only (e.g. Riccia) or differentiated into foot, seta and capsule (e.g. Marchantia).
Example - Riccia, Marchantia, Plasiochasma
II.Class: Anthocerotopsida:
1. The gametophyte is dersiventrally flat and thalloid.
2. The rhizoids are smooth walled and the ventral scales are absent.
3. Thallus is internally homogeneous.
4. Each cell of the thallus usually has a single (rarely two or more) laminate chloroplast with a conspicuous compound central pyrenoid.
5. The sex organs, Archegonia develop from superficial cells and antheridia from hypodermal cells.
6. The sporophyte is differentiated into a long cylindrical capsule, a small meristematic seta and a bulbous foot.
7. The elaters do not have thickening bands and as such are called pseudo elaters.
Example - Anthoceros, Notothylus
III.Class: Bryopsida:
1. The plant body has two growth stages-
(i) Protonema stage - it is the juvenile stage represented by prostrate, creeping, green and branched filamentous structure.
(ii) Leaf stage or gametophore - it consists of an erect cylindrical shoot with persistent leaves it bears sex organs.
2. The leaves are simple, sessile, and usually with a distinct midrib.
3. The axis is differentiated into a central conducting tissue and aperipheral cortex.
4. The sex organs are developed in groups at the apical of the stem. The plants are dioecious or monoecious.
5. The Antherozoid are biflagellate and spirally coiled.
6. The archegonia are stalked with a much elongated neck and a massive venter.
7. The capsule usually has a peristome which helps in the dispersal of spores.
Example - Sphagnum, Funaria, Polytrichum, Pogonatum.
Q.2. Give the classification and describe the characteristic features of liverworts.
Ans. Classification of Hepaticopsida: -
Enguler (1892) differentiated Hepaticopsida or hepaticae into the following three orders :
Verdomn (1932) divided the class Hepaticae into two subclasses.
Hepaticales and anthocerotiales. He included the following four orders in the subclasses Hepaticales.
Campbell (1936) placed both acrogynous and an a acrogynous junger manniales in a single order and included the order alobryales in the class Hepticopsida.
General character of liverworts or Hepaticopsida: -
Hepatica is the latin word for liver, and the Hepaticopsida are therefore popularly called liverworts. This name was applied to certain plants during the Middle ages due to their livershaped bodies and is a relic of the medieval belief in the “doctrine of Signatures.”
The class is represented by about 180 genera and 8500 species. Important characters are as follows :
1. The gametophyte which forms the main plant body, is independent dorsiventral and thalloid or faliose.
2. The plant body is prostrate, lobed and dichotomously branched in thalloid forms.
3. The ventral surface bears many unicellular unbranched, smooth walled and tuberculate rhizoids and scales.
4. When it is faliose, the leaves are nearly always without a midrib and are arrnaged on the axis either in two rows or three rows.
5. The gametophyte is internally either simple or made up of many tissues, but the photosynthetic cells usually contains numerous chloroplasts without pyrenoids.
6. The members of Hepaticopsida are homothallic (Monoecious e.g. R.gangetia, R. crystallina or heterothallic (dioecious) e.g. Riccia frostii, R. pearsonic.
7. The sex organs occupy dorsal or terminal position on the thallus. In thalloid liverworts the sex organs are either embedded in the thallus (e.g. Riccia) or are stalked (e.g. Marchantia) In faliose forms, however, they are always stalked.
8. The sporophyte is simple represented by capsule only (e.g. Riccia) or differentiated into foot, seta and capsule (e.g. Marchantia)
9. The sporogenous cell develop from the endothecium.
10.The capsule does not have sterile calumella. The only sterile cells are elaters.
11.The dehiscence of capsule is irregular and indefinite.
12.The spores give rise, to the gametophyte on germination.
13. There is a distinct alternation of generation.