Origin and evolution of bryophytes

Origin and evolution of bryophytes

• 2.
  Bryophytes are small,non vascular land plants, that require water for reproduction. The defining features of bryophytes are that their life cycle featuring alternating haploid and diploid generations with a dominant, branched gametophyte stage. The term "bryophyte” has its origin in the Greek language, referring to plants that swell upon hydration.
• 3.
  The bryophytes arequite soft and delicate and, therefore, they lack fossil records. All the views based on the evidence under the following three heads :-  Evidence from comparative morphology of the living plants  Evidence from ontogeny of the living plants  Evidence based on analogies with the living plants of other groups Bryologists are divided into two school of thoughts on the origin of bryophytes. One school of thoughts support Pteridophytean hypothesis and one support Algal hypothesis of the origin of bryophytes.
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   PTERIDOPHYTEAN HYPOTHESIS Accordingto this the bryophytes have been descended from pteridophytes by means of reduction. They formulated their argument on the basis of the following two features :- 1. Close similarity between the sex organs of the two groups. 2. Resemblance between sporogonium of Anthocerose, Sphagnum and terminal sporangium of fossil pteridophytes – Sporogonites and Horneophyton This theory is strongly supported by some of the scientists such as Lang(1917), Kidston and (1917), Scott(1923), Haskell(1949) and Kashyap(1919). Anthocerose Sphagnum Sporogonites Horneophyton
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  • Similarity oftheir pigments • Structure of cell wall • Food reserves • Reproductive methods • Life cycle Sporogonium of Mosses L. S. of Sporogonium of Anthoceros Affinities Scott introduce the idea (1911) • Presence of chlorophyll and plastids in the sporogonium of mosses and Anthoceros • Presence of stomata on the sporogonium of Anthoceros and the apophysis region of capsule of mosses
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  Equisetales Marchantiales Jungermanniales Anthocerotales Kashyap(1919) Haskell(1949)- He advanced the origin of the bryophytes from the algae through the Psilophytales by simplification.
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  Similarities • Photosynthetic pigmentslike chlorophyll α, Chlorophyll b, Carotene, leutine and violaxanthin • Starch as reserve food materials • Filamentous protonema in the juvenile stage Bower (1908): Bryophytes show resemblance with green algae (Chlorophyceae) • Amphibian nature • Presence of flagellated spermatozoid • Presence of free water at the time fertilization • Alga like protonema
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  Fritsch’s view (1916,1945) based on comparative study of various algal groups Sargassum Chaetophorales Fucales • Gradual reduction of conductive tissue in aerial plants (as in Sargassum) • Heterotrichous habit (as in chaetophorales) • Parenchymatous structure of erect filaments ( as in Laminariales and Fucales)
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  Smith (1955) Bryophytes haveoriginated from chlorophyceae, primitive form established in area having plenty of water and gradual changes from aquatic to terrestrial, this led to the establishment of more massive plant body and abundance of moisture As per Smith, Fritschiella; a member of chaetophorales may be probable nearer to the primitive ancestor for bryophytes
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  Again the supporters ofthis hypothesis also believed that sex organs of Bryophytes have been evolved from Ectocarpus algae.
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  There are twotheories regarding Evolution of bryophytes: I. The first theory is Up-grade or Progressive evolution theory II. The second one is Down-grade or Regressive evolution theory.  Progressive evolution theory There is progressive evolution which means that it starts with simple forms and terminates in complex forms. Cavers(1910) Campbell(1940) and Smith (1955) supported this. This theory revealed that the first evolved bryophyte was Sphaero-Riccia a hypothetical type which combined the present day Genus Sphaerocarpos (Proskaeur,1954).
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  Carves(1910) Proposed progressive Theory andshowed a Phylogenetic line of Evolution in bryophytes.
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  The primitive bryophyteswere mass-like in appearance.  Regressive (Down-Grade) Evolution Theory This view has been supported by Wettsein (1908), Kashyap (1919), Praskauer (1960), Zimmerman(1966), Mehra (1957) etc.
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  Bryophyte Hepaticopsida 330 genera; 8000species Anthocerotopsida 7 genera and a single order Bryopsida 700 genera 14000 speceis Order Calobryales (Moss like hepatics) Jungermanniales (Scale moss hepatics) Metzgeriales (Multiform thallus) Marchantiales (Chambered hepatics Sphaerocarpales (Bottle shaped) Monocleales (Giant thallose) Order Anthocerotales Order Spahagnales Archidiales Tetraphidales Andreales Bryales Polytrichales Takakiales Based on the structure of gametophyte Based on the characters of gametophyte and sporophyte, especially peristome
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  Bryum capillaraePolytrichum piliferum Cyathodiumcavernarum Phaeoceros laevis ARUNACHAL PRADESH ASSAM
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  MANIPUR Philonotis fontana Philonotishastata MEGHALAYA Brachythecium buchananii Targionia hypophylla
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  MIZORAM NAGALAND Bryum alpinum Atrichumundulatum Dumortiera hirsuta Frullania raddi
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  Asterella khasiana Bryumpseudotriquetrum SIKKIM TRIPURA Trematodon longicollis Garckea flexuosa