Sargassum

CLASSIFICATION OF SARGASSUM

Sub-division :- Algae

Class :- Phaeophyceae

Order :- Fucales

Family :- Sargassaceae

Genus :- Sargassum

Sargassum is marine in habitat and remains restricted to tropical seas, mainly of southern hemisphere. In India, species of this genus are found along the east coast, west coast, and Andman and Nicobar islands.

EXTERNAL FEATURES OF THALLUS​ OF SARGASSUM

• Thallus is erect, thalloid and branched.
• It remains attached to the substratum by a discoid holdfast.
• Main axis stands out from the holdfast. It varies from a few to many centimeters in height.
• Main axis bears large number of primary laterals forming a larger part of vegetative structure. Branches are radially symmetrical and spirally arranged.
• Secondary branches are repeatedly branched.
• Many branches are flattened along the plane of branching into leaf-like structures called ‘leaves’.
• Leaves are narrow and their margins are mostly serrate. A few species also show a clear mid-rib.
• In the lower parts, leaves are replaced by air bladders. However, leaf or its part is modified almost at any place into an air bladder.
• Leaves show minute pores on both of the surfaces which are ostioles (or openings) of conceptacles (sterile) or cryptostomata or cryptoblasts.
• In the axils of foliaceous branches (leaves) is situated a series of repeatedly branched receptacles which bear reproductive structures.

INTERNAL STRUCTURE OF AXIS OF SARGASSUM

• The section is almost circular in outline.
• It is differentiated into three regions :
  1. meristoderm,
  2. cortex
• Meristoderm is the outermost single celled layer of meristematic cells. It consists of many, small and compactly placed cells covered by mucilage. Cells are rich in chromatophores and reserve food material.
• Cells of the meristoderm are photosynthetically active and, therefore, constitute assimilatory region.
• Cortex forms the major part of the axis. Cells are narrow and elongated with many intercellular spaces. Cells possess large amount of reserve food material. This region is also known as storage region.
• Medulla occupies the central part of the axis. It consists of narrow, elongated and doublewalled cells, inner wall being thin than the outer.
• The medulla transports water and essential nutrients. Hence, it is a also called as conducting region

INTERNAL STRUCTURE OF LEAF OF SARGASSUM​

• s. of leaf shows 3 regions similar to those found in axis. These are-meristoderm, cortex and medulla.
• Meristoderm is the outermost layer. Cells are small, compactly arranged and rich m chromatophores and reserve food.
• Cortex is a major part of the tissues. Cells are thin and contain large amount of reserve food material.
• Medulla occurs only in central region of the leaf indicating mid-rib. It is absent from the wings.
• In the leaf many sterile conceptac1es are distributed on both of its surfaces (also known as cryptostomata or cryptoblasts).
• Each cryptoblat opens to the exterior by an opening- ostiole (visible externally as black dots or pores).

INTERNAL STRUCTURE OF AIR BLADDER​

• Air bladder appears circular in outline.
• It is enveloped by a distinct mucilage.
• s. shows outermost meristoderm, followed by cortex and the central air cavity.
• Meristoderm is made of radially elongated thin walled cells. It is followed by a large and thin-celled cortex.
• In the center is a large air cavity filled with gases.
• Air bladders help in gaseous exchange and buyoancy.

INTERNAL STRUCTURE OF MALE CONCEPTACLE​

• Plants may be monoecious or dioecious.
• Antheridia are found in male conceptacles.
• Conceptacles occur only in specialized branch system called receptacle or receptacular branch.
• Male conceptacles are externally smooth.
• Many conceptacles are found in a male receptacular branch.
• Each conceptacle is a flask-shaped cavity opening by a pore called ostiole.
• Wall of the conceptacle is made of small and flat cells rich in chromatophores.
• Numerous multicellular hairs arising from near the ostiole project outside. These are called periphyses.
• Other types of multicellular hairs arising from the floor of the cavity are called paraphyses.
• Some of paraphyses are branched and hold one or more antheridia at the tips of the branches.
• Each antheridium has a thick wall made of two layers.
• On maturity about 64 biflagellate antherozoids are produced.

INTERNAL STRUCTURE OF FEMALE CONCEPTACLE​

• The plants may be monoecious or dioecious.
• Oogonia are found in female conceptacles.
• Conceptacles occur only in specialized branch system called receptacle or receptacular branch.
• The female receptacular branch is spinous.
• It bears many female conceptacles.
• Conceptacle is a flask-shaped cavity opening by a pore called ostiole.
• Many multicellular, unbranched hairs arising from near the ostiole called periphyses protrude outside.
• The wall of the conceptacle is lined by small and flat cells, rich in chromatophores.
• A few multicellular, unbranched hairs arise from the floor of the cavity and are called paraphyses.
• Numerous oogonia arise directly from the wall of the conceptacle.
• Oogonium is sessile or shortly stalked (most of the stalk cell being embedded in the wall).
• Each oogonium is oval to sub-spherical with a three layered wall.
• At maturity oogonium has a single, large and uninucleate egg.

IDENTIFICATION OF SARGASSUM

• Sub-division– Algae
  1. Presence of a simple thallus.
  2. Chlorophyll present
  3. Cell wall made of cellulose.
• Class– Phaeophyceae
  1. Yellowish-brown chromatophores.
  2. Photosynthetic reserve-Iaminarin and mannitol.
  3. Motile reproductive cell-pyriform and flagellated
  4. Flagella laterally inserted and unequal.
• Order– Fucales
  1. Plants parenchymatous with complex morphological and anatomical differentiation
  2. Medulla filamentous
  3. Absence of asexual reproduction
  4. Sex organs in conceptacles.
• Family – Sargassaceae
  1. Axes terete, bearing distinct foliar organs.
  2. Vesicles usually present, lateral or immersed in the terminal branchlets.
  3. Branching of the thallus radial to the central axis.
• Genus – Sargassum
  1. Foliar organs narrow, branched, leaflife with a distinct mid-rib.
  2. Vesicles generally lateral
  3. Fertile branches (receptacles) lateral, or terminal panicles.

REFERENCES :-

• https://en.wikipedia.org/wiki/Sargassum
• https://www.shutterstock.com/search/sargassum