Introduction to Bryophytes ( Bsc first year)

 General Characters

General characters of bryophytes are as follows:

1. Bryophytes are commonly found in moist and shady places like damp walls,

wooden plugs, wet rocks, tree trunk, swamps etc. A few bryophytes are aquatic

(Riccia, Ricciocarpus) etc.

2. Plant body is independent gametophytic structure which is thalloid in primitive

bryophytes but differentiated into root like (rhizoid), stem like (cauloid) and leaf

like (phylloid) in advanced bryophytes.

3. Vascular and mechanical tissues are absent in plant body.

4. Bryophytes consist of unicellular or multicellular rhizoids that help in the absorp

and mineral from soil and also help in the fixation to the substratum.

5. Reproduction takes place by vegetative and sexual methods.

6. Vegetative reproduction is the most common method of reproduction that takes

place by fragmentation, adventitious branches, tubers, gemmae etc.

7. Sexual reproduction takes place by oogamy (flagellate sperms or motile anther

formed in male reproductive organ and non-motile egg is formed in female

reproductive organ)

8. Sex organs are multicellular and jacketed.

9. Male sex organ is called antheridium and female sex organ is called

archegonium. Biflagellate sperms or antherozoids are formed in antheridium. Non-

motile egg is formed in archegonium.

10. Water is necessary for fertilization.

11. The sporophyte is totally or partially dependent on gametophyte which is

differentiated in foot, seta and capsule.

12. Capsule or sporangium is fertile part of sporophyte. Diploid spore mother cells

present in capsule divide by meiosis and form haploid spores.

13. All spores are similar types (homospory).

14. Life cycle of bryophytes consists of two cytologically, physiologically and

morphologically distinct generations; haploid gametophytic and diploid sporophytic

generation which come alternately to complete the life cycle. The phenomenon is

called alternation of generation.

15. Marchantia, Riccia, Ricciocarpus, Porella, Funaria, Polytrichum, Pogonatum,

Sphagnum etc. are some examples of bryophytes.

Distribution

 Bryophytes are distributed throughout the world, from polar and alpine regions to

the tropics. They are most abundant in climates that are constantly humid and

equable.

 The greatest diversity is at tropical and subtropical region.

 Bryophytes do not live in extremely arid sites or in seawater, although some are

found in perennially damp environments within arid regions and a few are found

on seashores.

 The geographic distribution patterns of bryophytes are similar to those of the

terrestrial vascular plants, except that there are many genera and families and a

few species of bryophytes that are almost cosmopolitan.

A few bryophytes are aquatic.

 Bryophytes are represented by 960 genera and 25,000 species. They are

cosmopolitan in distribution and are found growing both in the temperate and

tropical regions of the world.

Habitat

 Bryophytes grow densely in moist and shady places and form thick carpets or 

mats on damp soils, rocks, bark of trees especially during rainy season.

 Small in size, but they can be very conspicuous growing as extensive mats in 

woodland, as cushions on walls, rocks and tree trunks, and as pioneer colonists 

of disturbed habitats. 

 Majority of the species are terrestrial but a few species grow in fresh water 

 Riccia fluitans, Ricciocarpos natans, Riella etc.

 Bryophytes are not found in sea but some mosses are found growing in the      

Life cycle

 The life cycle of bryophytes shows two distinct phases namely a haploid

gametophytic phase and a diploid sporophytic phase alternating with each other.

 The adult plant body represents the gametophyte. A short lived sporophyte occurs

as a parasite on the gametophyte.

Gametophyte

 A stage in the life cycle of bryophyte that undergoes alternation of generations.

 It is a haploid multicellular organism that develops from a haploid spore that has

one set of chromosomes.

 The gametophyte is the sexual phase in the life cycle of bryophytes. It develops

sex organs that produce gametes, haploid sex cells that participate in

fertilization to form a diploid zygote.

 Cell division of the zygote results in a new diploid multicellular organism, the

second stage in the life cycle known as the sporophyte, the function of which is

to produce haploid spores by meiosis.

 In bryophytes the gametophyte is the most visible stage of the life cycle.

 The bryophyte gametophyte is longer lived, nutritionally independent, and the

sporophytes are typically attached to the gametophytes and dependent on them.

 It is the adult plant body in bryophytes. It is either thalloid or in the form of a leafy

shoot with stem like and leaf like structures.

 Roots are absent and instead thread like rhizoids are present.

 Vascular tissues xylem and phloem are absent.

 The mature gametophyte bears male reproductive organs called antheridia and

female reproductive organs called archegonia.

 The antheridia have a club shaped body and a stalk.

They produce flagellated male gametes called antherozoids or sperms.

 The archegonia are flask shaped with a well defined venter and neck.

 The venter encloses a venter canal cell and an egg cell while the neck encloses

a variable number of neck canal cells.

 The antherozoids liberated from antheridia, swim in a film of water and reach the

archegonia.

 They are attracted into the archegonia to bring about fertilization. 

Sexual Reproduction in Bryophytes

 Sexual reproduction is highly oogamous.

 Male and female sex organs are known as antheridia ( antheridium) and

archegonia (archegonium) respectively.

 Sex organs are jacketed and multilayered.

 Antheridium is stalked, pear shaped or oblong and has an outer one cell thick

jacket which encloses a mass of fertile cells called androcytes. Each androcyte

metamorphoses into biflagellate antherozoid.

During the formation of spores, the spore mother cells divide meiotically and

haploid spores are produced.

 The production of the spores is the beginning of the gametophytic or haploid

phase.

 The spores germinate and produce gametophytic or haploid phase.

 The spores germinate and produce gametophytes which bear sex organs

Ultimately the gametic union takes place and zygote is resulted It is diploid (2n).

 This is the beginning of the sporophytic or diploid phase This way, the

sporophyte generation intervenes between fertilization syngamy and meiosis

(reduction division) and gametophyte generation intervenes between meiosis

and fertilization

Sporophyte

 Without resting period, the zygote undergoes repeated divisions to form a

multicellular structure called the embryo.

 The first division of the zygote is always transverse and the outer cell develops

into embryo such an embryogeny is called exoscopic.

 Embryo develops into a sporophyte or sporogonium.

 The sporophyte is usually differentiated into foot, seta and capsule.

 In certain cases it is represented only by capsule in Riccia or by foot and

capsule in Corsinia.

Sporophyte is attached to parent gametophytic plant body throughout its life. It

partially or completely depends on it for nutrition.

 Foot is basal, bulbous structure. It is embedded in the tissue of parent

gametophyte. Its main function is to absorb the food material from the parent

gametophyte.

 Seta is present between the foot and capsule. It elongates and pushes the

capsule through protective layers. It also conducts the food to the capsule

absorbed by foot.

 Capsule is the terminal part of the sporogonium and its function is to produce

spores.

All bryophytes are homosporous i.e. all spores are similar in shape, size and

structure.

 Capsule produces sporogenous tissue which develops entirely into spore

mother cells. It is differentiated into spore mother cells and elater mother cells.

 Spore mother cells divide diagonally to produce asexually four haploid spores

which are arranged in tetrahedral tetrads.

 Elater mother cells develop into elaters. Elaters are present in liverworts and

absent in mosses.

Sexual Reproduction in Bryophytes

 Sexual reproduction is highly oogamous.

 Male and female sex organs are known as antheridia ( antheridium) and

archegonia (archegonium) respectively.

 Sex organs are jacketed and multilayered.

 Antheridium is stalked, pear shaped or oblong and has an outer one cell thick

jacket which encloses a mass of fertile cells called androcytes. Each androcyte

metamorphoses into biflagellate antherozoid.

Archegonium is stalked, flask shaped structure It has a basal swollen portion

called venter and an elongated neck The neck is filled with many neck canal

cells whereas venter has a large egg cell and a small venter canal cell.

 Antherozoids are attracted towards the neck of the archegonium

chemotactically by certain substances (like sugars, malic acid, proteins,

inorganic salts of potassium etc. present in the mucilaginous substance formed

by the degeneration of neck canal cells and venter canal cell.

 Water is essential for fertilization

 The fertilized egg or zygote is the beginning of the sporophytic phase It is

retained within the venter of the archegonium.

Alternation of generation

 The life cycle of a bryophyte shows regular alternation of gametophytic and

sporophytic generations.

 The haploid phase is the gametophyte or sexual generation. It bears the

sexual reproductive organs which produce gametes, i.e. antherozoids and

eggs.

 With the result of gametic union a zygote is formed which develops into a

sporophyte.

 This is the diploid phase (2n). The sporophyte produces spores which always

germinate to form gametophytes.

During the formation of spores, the spore mother cells divide meiotically and

haploid spores are produced.

 The production of the spores is the beginning of the gametophytic or haploid

phase.

 The spores germinate and produce gametophytic or haploid phase.

 The spores germinate and produce gametophytes which bear sex organs

Ultimately the gametic union takes place and zygote is resulted It is diploid (2n).

 This is the beginning of the sporophytic or diploid phase This way, the

sporophyte generation intervenes between fertilization syngamy and meiosis

(reduction division) and gametophyte generation intervenes between meiosis

and fertilization.