Characteristics of Bryophytes (Life Cycle and Reproduction of Phylum Bryophyta)


Characters of Bryophytes

Mosses and Liverworts General Characteristics (Key points with PPT)

Ø  Bryophytes are the most simplest and most primitive land plants

Ø  Name bryophyte is derived from two words; ‘Bryon’ = moss; ‘phyton’ = plant

Ø  At present the phylum Bryophyta includes  ~ 960 genera and ~ 24000 species

Habit and Habitat of Bryophytes

Ø  They are cosmopolitan in distribution

Ø  Bryophytes are quite uncommon in marine environments

Ø  Bryophytes are terrestrial plants but require water at every stages in their life cycle

Ø  They grow usually in moist and shady places

Ø  They fail to complete its life cycle in the absence of water

Ø  Few bryophytes are truly aquatic and underwater forms(example Riccia fluitans)

Sphagnum.flexuosum

Sphagnum moss (source wikipedia)

Ø  Peat moss (Sphagnum moss) grown in bogs and marshy areas

Ø  Porella is an epiphytic bryophyte that grow on tree trunks

Ø  Radulla protensa is an epiphyllous bryophyte grow on the surface of leaves

Ø  Tortula desortorum is a xerophytic bryophyte growing in deserts

Ø  Bryophytes are fundamentally land plants

Ø  The land adaptations of bryophytes are:

§  Possess root like rhizoids to absorb water from soil

§  Free surface of epidermis is coated with water proof waxy coating to prevent water lose and protect against desiccation

§  They possess stomata like structures for gaseous exchange

§  Possess multicellular sex organs surrounded by sterile jacket

§  After fertilization the zygote is left inside the archegonium to provide nutrition for the sporophyte development

§  These features helps bryophytes to live in land condition

RicciaFluitans1.jpg

Riccia fluitans (source wikipedia)

Why Bryophytes the Amphibians of Plant Kingdom?

Ø  Amphibians in the animal kingdom lives in water as well as in land

Ø  Similarly bryophytes represented by liverworts, hornworts and mosses grow well in the areas between water and terrestrial habitats (amphibious zone)

Ø  Bryophytes are dependent on water to complete their life cycle

Ø  Presence of water is required and essential for the:

§  Dehiscence of mature antheridia

§  Liberation of antherozoids form antheridia

§  Transfer of antherozoids form antheridia to archegonia

§  Opening of archegonial neck

§  Movement of flagellated antherozoids into the archegonial neck.

Ø  Life cycle of bryophytes will not complete in the absence of water

Ø  Thus they are called as the amphibians of plant kingdom.

Anthoceros agrestis 060910c

Anthoceros (hornwort) (source wikipedia)

Gametophyte of bryophyte

Ø  Life cycle consists of gametophytic and sporophytic phases (generations)

Ø  Gametophytic and sporophytic generations are physically connected

Ø  Gametophytic and Sporophytic phases are Heteromorphic (morphologically distinct)

Ø  Characteristic of gametophytic generation of Bryophyte:

@.   Gametophytic generation is more conspicuous phase in life cycle

@.    Gametophytic generation is long lived and prominent phase

@.    It is independent, green autotrophic phase

@.    Gametophytic plant is fleshy

@.    In lower forms gametophyte is undifferentiated and thalloid

@.    In higher forms, gametophyte is differentiated into root like, leaf like and stem like structures

Physcomitrella Sporophyt

Moss Capsule (source wikipedia)

Ø  Characteristics of sporophytic generation of Bryophyte:

@.    Sporophytic generation is less conspicuous phase in life cycle

@.    Sporophytic generation is short lived  

@.    Sporophyte is completely dependent on gametophytic plant for nutrition

@.    Usually differentiated into foot, seta and capsule

Ø  In primitive forms (Riccia and Marchantia) gametophyte is undifferentiated, prostrate and thalloid

Ø  In advanced forms (mosses) plant body is erect, differentiated into stem (axis), lateral appendages (leaves) and rhizoids

Ø  True roots are absent in bryophytes

Ø  Rhizoids are present, rhizoids helps in anchorage and absorption

Ø  Rhizoids may be unicellular and un-branched to multicellular branched

Ø  Sometimes multicellular scales may be present

Ø  Scales helps to protect growing region of the thallus

Ø  Plant body consists of parenchymatous cells only

Ø  Thick walled and lignified cells are completely absent in all phases

Ø  Vascular tissue are completely absent

Ø  Plant body sometimes internally differentiated into photosynthetic and storage zone (labour division)

Ø  Xylem and phloem are absent

Bryophyta reproduction:

Ø  They reproduce by vegetative and sexual reproduction

MarchantiaPolymorpha.jpg

Marchantia with Gemmae (source wikipedia)

Ø  Vegetative multiplication takes place by:

§  Death and decay of older parts

§  Fragmentation of thallus

§  Adventitious branches

§  Tuber formation

§  Production of gemmae on gemmae cups

Sexual reproduction in bryophytes:

Ø  Sexual reproduction is oogamous type

Ø  Sex organs are multicellular

Antheridia

Antheridia (LS) (source wikipedia)

Ø  Sex organs are more complex than thallophytes (algae, fungi and lichens)

Ø  Male sex organ is called antheridia

Ø  Antheridia are stalked and globose

Ø  They have one cell thick sterile jacket around it for protection

Ø  Jacket surrounds a solid mass of fertile cells called antherocytes

Ø  Antherocytes metamorphose into antherozoids

Ø  Antherozoids are bi-flagellate and thus they are motile (can swim in water)

Archegonium

Archegonia (LS) (source wikipedia)

Ø  Female sex organ is called archegonia

Ø  Archegonia is a flask shaped structure

Ø  Archegonia have basal swollen venter and an elongated upper part called neck

Ø  The ventre and neck are surrounded by one layer thick sterile jacket cells

Ø  Four to six neck canals cells and one venter canal cell is present

Fertilization in bryophytes

Ø  Water is necessary for fertilization




Ø  When antheridia matures, their sterile jacket disintegrate and liberate the motile anthropoids to the surrounding thin film of water

Ø  When archegonia matures, the neck canal cells and venter canal cell disintegrate and forms a mucilage mass

Ø  The cover cells of the archegonia opens and the mucilage ooze out through the pore into the thin film of water

Ø  Antherozoids are attracted by chemicals present in the mucilage and move towards it by chemotaxis through the thin film of water

Ø  Antherozoids enters into the archegonium through neck and venter

Ø  Antherozoids fuse with egg to from a diploid zygote

Sporophyte of bryophyte

Mosses on a tombstone.jpg

Bryum Gametophyte & Sprophyte (source wikipedia)

Ø  Sporophyte develop from embryo

Ø  Zygote is the first stage in the diploid sporophytic generation

Ø  Zygote does not have any resting period

Ø  Zygote mitotically divide immediately after fertilization

Ø  Bryophyts shows exoscopic mode of embryo development

Ø  First division of zygote is always transverse to produce two cells (outer cell and inner cell)

Ø  Outer cell give rise to embryo

Ø  Embryo develops within the ventre of archegonium

DEV035048A

Archegonia (source wikipedia)

Ø  Sporophyte is simple structure without rhizoids stem or leaves

Ø  Sporophyte is completely dependent on gametophyte for nourishment

Ø  Sporophyte is s projecting structure in most of the forms, it project out from the gametophytic tissue

Ø  Sporophyte is differentiated into foot, seta and capsule

Ø  Sporogenous cells present in the capsule divide meiotically to produce haploid spores

Ø  All spores are similar in shape and size (homosporous)

Ø  Sometimes elaters are present

Ø  Elaters are hygroscopic and they helps in spore dispersal

Ø  Spores are non-motile and they disperse exclusively by wind or water current

Ø  Under favorable condition the spores germinate to form the gametophytic plant

Ø  In lower forms, the germination of spores is by the formation of a germ tube which later divide to give rise the younger gametophyte (Riccia, Marchantia)

Ø  In advanced forms (mosses) spores germinate to form a filamentous branched  protonema

Ø  From the protonema, many gametophytic plants arises

Bryophyta Life Cycle (Life cycle of mosses)

Ø  Life cycle of bryophytes is characterized by the alternation of two morphologically distinct phases

Ø  One phase is haploid gametophyte

Ø  Other phase is diploid sporophyte

Ø  Gametophytic phase is independent, autotrophic haploid and bears gametes

Ø  It develops from the spores produced by sporophyte

Ø  Male and female gametes represent the last phase of gametophytic generation

Ø  Haploid male and female gametes fuse to forms a diploid zygote

Ø  Zygote represent the first phase of sporophytic generation

Ø  Sporophyte is simple, completely dependent on gametophyte for nutrition

Ø  Sporogenous tissue in the sporophyte divide meiotically to produce haploid spores

Ø  The spores germinate to form haploid gametophyte

Moss alternation of generations 03-2012

Life Cycle of Bryophytes (source wikipedia)

Economic importance of Bryophytes:

Ø  Mosses are often used for soil conditioning, they increase the aeration and water holding capacity of soil.

Ø  Sphagnum moss is used extensively in potting mixtures for growing plants in nurseries and conservatories

Ø  Sphagnum moss is also used in air layering

Ø  Bryophytes are ecological indicators, they indicate moist, and wet weather condition

Ø  Some mosses are air pollution indicators, their absence in the area indicate air pollution.

Ø  Some bryophytes indicate copper in the soil (Mielichhoferia elongata, M. mielichhoferi, and Scopelophila)

Ø  Sphagnum indicate acid condition in the soil

Ø  Used to prevent soil erosion (Barbula, Bryum)

Ø  Anthoceros can fix nitrogen and can enrich the soil nutrients

Ø  Many mosses are attractive and they are used in gardening

Ø  Some mosses are used as packing materials, they also have good insect repelling activity

Ø  Peat moss is a good fuel, it is extensively used as fuel in many European countries

Ø  Sphagnum moss is used for the preparation of absorbent bandages, they also have good antiseptic properties.

Polytrichum strictum

Polytrichum (source wikipedia)

Ø  Marchantia polymorpha is used in the treatment of pulmonary tuberculosis

Ø  Some species of Polytrichum has been used for the treatment of kidney stones

Key questions:

  1. What are bryophytes?
  2. What are the characteristics of bryophytes?
  3. Explain the life cycle of bryophytes.
  4. Explain the reproduction in bryophyte.
  5. Explain the structure of Antheridium and Archegonium of Bryophyta.
  6. Explain alternation of generation in bryophytes.
  7. What are the economic importance of bryophytes?
  8. What are the ecological importance of bryophytes?

Bryophytes Short Notes


You may also like…

@. Algae Characteristics

@. Lichen Characteristics

@. Life Cycles in Algae

@. Pigmentation in Algae

@. Botany Lecture Notes

@. Biology MCQ

@. Biology PPT

@. Video Tutorials

@. Question Bank

@. Biology Exams


You can download the PPT of this post from our SLIDESHARE Account


Please Share for your Students, Colleagues, Friends and Relatives…

Facebooktwittergoogle_pluspinterestlinkedin
Posted in Botany, Bryophyte, Lecture Notes and tagged , , , .