POLYSIPHONIA

CLASSIFICATION OF POLYSIPHONIA

Sub-division :- Algae

Class :- Rhodophyceae

Sub class :- Florideae

Order :- Ceramiales

Family :- Rhodomelaceae

Genus :- Polysiphonia

Species of Polysiphonia are exclusively marine.  These are most commonly found along the Atlantic  and Pacific coasts, in littoral and sub-littoral regions.  A few species occur as epiphytes on mangroves or  brown seaweeds. A small number of species are  also found along the Indian coasts. 

EXTERNAL FEATURES OF THALLUS​ AND A CELL

Polysiphonia. Thallus to show habit.

COMMENTS:-

  • Plant body is filamentous. Filaments are  multicellular, branched and polysiphonous. 
  • Branching is dichotomous. Each branch terminates into a single celled apex, followed  by a number of flat cells.
  • Thallus is polysiphonous i.e. made of series of  parallel filaments.  
  • Centre is occupied by a large barrel shaped  cell (axial cell or central siphon). It is  surrounded by 4-24 peripheral cells (pericentral  siphons).  

 Polysiphonia. A single cell.

  • In the apical region, two or three cells below  the apical cell, uniseriate, dichotomously divided,  gradually tapering and multicellular filament is  produced. It is known as trichoblast.  
  • Many species remain attached to the substratum  by thick walled, richly lobed and  unicellular rhizoids (attaching organs) which  arise from the peripheral cells of the creeping  system.

Polysiphonio:. A part of thallus with branches.

  • The cell wall is thick. Cell is uninucleate. It has a large central vacuole. Chromatophores are small, discoid and many times without pyrenoids. Reserve food is in the form of starch grains-floridoside.
  • The neighbouring cells are connected with one another by cytoplasmic lining known as pit connections.

Polysiphonia. A part of thallus showing rhizoids.

SPERMATANGIA

COMMENTS :-

  • The genus shows male plants bearing antheridia.
  •  Antheridia are produced in clusters by fertile  trichoblasts situated near the apex.  
  • Antheridium is known as spermatangium.  It is oval in shape, naked (without outer  membrane) and contains many non-motile  spermatia.  
  •  Each spermatium is small, oval to spherical,  uninucleate and non-motile.

PolysiphoniIL T.s. thallus.

STRUCTURE OF POLYSIPHONIA​

COMMENTS:-

  • The carpogonia is present on the female plants inside the procarp.
  • Procarp is urn-shaped body. The wall is called  pericarp that has an opening known as ostiole. 
  •  A long, tubular, receptive organ called  trichogyne protrudes out of the ostiole. 
  • At the base of trichogyne lies a swollen part,  called carpogonium with a single female nucleus.  

Polysiphonia. A-B A. Cluster of spennatangia, B. A spennatangium.

CYSTOCARP OF POLYSIPHONIA​

COMMENTS :-

  • Cystocarp is a post-fertilization product. The  thallus bearing this structure forms a phase  called carposporophyte.  
  • This oval or urn-shaped structure is attached to  a lateral branch.  
  • Cystocarp opens to the exterior by an opening  called ostiole.  
  •  Wall of the cystocarp is called pericarp and is  composed of a single layer of cells.
  • Carpospores are produced from he base of the cystocarp. These are arranged in single spherical layer.
  • Each carpospore is oval, uninucleate and diploid

Polysiphonia. A part of thallus with cystocarp.

STRUCTURE OF TETRASPOROPHYTE AND TETRASPORANGIUM

COMMENTS :-

  • Tetrasporophytes are morphologically similar to male and the female gametophytes.
  • The thallus is polysiphonous being made of a central siphon surrounded by pericentral siphons.
  • A cell shows a nucleus, discoid chromatophores and pit connections.
  • The plant is diploid and bears tetrasporangia in longitudinal series, produced mostly by pericentral cells.
  • Tetrasporangia are small and spherical bodies borne on short one-celled stalk.

Polysiphonia. A part of thallus with tetrasporangia.

IDENTIFICATION OF POLYSIPHONIA

  • Sub-division Algae
    1. Thallus simple,
    2. Chlorophyll present.
    3. Cell walls of cellulose.  
  • Class Rhodophyceae
    1. Chromatophores pure red to dark purple,
    2. Photosynthetic reserve floridoside,
    3. Male  gametes non-motile,
    4. Female reproductive organ with  a receptive structure-trichogyne,
    5. Post-fertilization  product–cystocarp.  
  • Sub-class Florideae.
    1. Thallus basically filamentous,
    2. Pit  connections between sister cells,
    3. Cells with more than  one chromatophore,
    4. Carpogonium highly specialized.  
  • Order Ceramiales.
    1. Thalli uni-multiaxial or filamentous 
    2. Filaments corticated, polysiphonous,
    3. Spermatangia in clusters,
    4. Presence of trichoblasts.  
  • Family Rhodomelaceae.
    1. Axes polysiphonous,
    2. Axes  naked, corticated or covered with branches,
    3. Main axis  surrounded with pericentrals,
    4. Plants bushy, sparingly
  • GenusPolysiphonia
    1. Ultimate branches uncorticated
    2. Tetrasporangia borne singly.

POLYSIPHONIA

REFERENCES :-

  • https://en.wikipedia.org/wiki/Polysiphonia
  • Text book of practical :- botany


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