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

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).  

• 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.

• 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.

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.

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.  

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

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.

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
• Genus – Polysiphonia
  1. Ultimate branches uncorticated
  2. Tetrasporangia borne singly.

REFERENCES :-

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

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