knowledge mind: sargassum: classification, structure, reproduction,lifecycle

sargassum

Division: phaeophyta

Subdivision: phaeophyceae

Class: cyclosporae

Order: fucales

Family: sargassaceae

Genus: sargassum

· the main axis.
· The main ax Thallus of sargassum is diploid and sporophytic.it is erect branched and differentiated into holdfast and is bears many leaves like lateral branches and air bladders.
· The holdfast is a dicoid structure which remains attached to the substratum.
· The main axis is erect,cylindrical or flattened;it bears large number of primary lateral arranged spirally.
· They have unlimited growth so called as long shoots.
· The main axis as well as primary lateral bears flat leaf like branches known as secondary lateral/leaves.
· The secondary laterals present in upper portion bears axillary branches.some branch gets modify into spherical air bladders.
· They are filled with air and help the plant in floating.
· The other axillary branches are repeatedly branched flattened called as’conceptacle’.

· The transverse section of main is circular and is differentiated into 3 distinct region
· 1)meristoderm-phothsynthetic region
· 2)cortex-contain reserve food material
3)medulla-made of thick walled narrow and elongated cells.function is to transport water and metabolies to different parts of thallus.

· It reproduces by vegetative and sexual methods. Asexual reproduction is absent.
· Vegetative reproduction takes place by fragmentation.
· Sexual reproduction is oogamous.
· Sex organs are produced in special flask shaped cavities called conceptacles which are borne on the receptacles.
· Male and female sex organs are produced on separate conceptacles.
· In homothallic species antheridia and oogonia are present in the same conceptacle or different conceptacles on separate plants.
· Conceptacles develops from a single cell.
· They become flask shaped bodies having an opening called ostiole.

· The antheridium is oval in shape surrounded by 2 layers.
· They remain attached to the base of the conceptacle by stalk cell.
· At maturity, the antheridium is detached from the stalk and comes out through the ostiole.
· When antheridia come in water, the antherozoids are liberated.
· Along with antheridia, paraphyses also develop inside the conceptacle. They are sterile.

· The oogamous develop from the basal fertile layer of the conceptacle.
· The basal cell is very small and bear oogonial cell. It is spherical in shape. It has dence cytoplasm and oil droplets.
· The functional nucleus is located in the centre of the oogonium. The mature oogonia are discharged from the conceptacle.

· A large number of antherozoids surrounds the oogonium and attach to the oogonial wall with the flagells.
· Only one antherozoid penetrates the oogonial wall.
· After fertilization the male and female nuclei fuses to form a diploid zygote.
· The zygote germinates immediately after fertilization. It gets attached to solid substratum in sea water.
· The lower cell forms the rhizoids and the upper cell undergoes repeated division to form diploid thallus.

The life cycle does not show any alternation of generation. Thallus is diploid and sporophyte. The haploid phase is represented only by gamets.