• Sargassum is a marine algae which popularly called as the Gulf Weed.
• The Sargassum plant is macroscopic and more or less bushy in habit.
• Most of the species occur in tropical or temperate zones attached along
the rocky shores. Some species occur along the Indian coast(East and West)
and that of the Australian sea and also in Japan.
• Name of some common Indian Sargassum Sp. Is-
a) S. tennerimum
b) S. carpophyllum
c) S. Duplication
d) S. Plagiophyllum
e) S. ilicifolium
f) S. mycosystum
• Sargassum is a diploid sporophyte.
• It has a main axis of approximately 30 cm long or more.
• It bears richly branched Primary lateral. This primary lateral has unlimited
growth and also called as long shoot.
• The long shoot bears numerous secondary laterals of limited growth.
• Of the latter the latter the basal one is usually most conspicuous. It is shaped like
• The basal member or members of auxiliary branch system are swollen into
stalked and rounded structures called air bladders. This air bladders contained
the same gases as the at the atmosphere and helps the plant to keep floating
upon the surface of water.
• The subsequent members of the auxiliary branched system may be cylindrical or
flattened. They are called the receptacles. The receptacles are formed when the
plant became fertile.
• The receptacles are stud with fertile, flask-shaped conceptacles.
Structure of a Sargassum peron.
ab- air bladder; rc- receptacles bearing conceptacles; ax-
auxiliary branch; lb- lateral branch; md-midrib; l- bearing
Structure of Sargassum
A part of thallus showing laterals and
Basal portion of the plant of Sargassum enerve.
ab- air bludder; abr- auxillary branch; bl- basal lateral; l- lateral branch; ma- main axis; hf- holdfast
Structure of the thallus
• Meristoderm- It is a peripheral layer of columnar cells without any air spaces
between them. It contains three layers of cells – Palaside layer, hypodermal
layer and cutical.
• Cortex- Within the hypodermal layer there is cortex consisting of thick-walled
• Medulla- the central zone is called as Medulla. The cells of this region is
loosely arranged. They are narrow and elongated. The outer cells of the
medulla have thick walls where as the inner cells have thin walls.
• Reproduction of Sargassum takes place by two methods-
• Vegetative method
• Sexual method
• Vegetative method- This process is done fragmentation. The older
parts die and decay separating the younger parts. The latter continue
to grow and finally developed to full-fledge Sargassum plant.
• S. natans and S. hystrix multiply exclusively by this method.
• Sexual Reproduction- It is the usual method of reproduction and is
• The sex organs produced in flask-shaped cavities called the conceptacles
borne on the sporophyte plant.
• Development of conceptacles.
• Development of sex organs. For male it is called as Antheridia whereas in
female it is called Oogonium.
• Germination of Zygote.
Oogonium of Sargassum Sp. with attached to conceptacle
mst- Oogonia attached to the conceptacle wall long gelatinous stalks; ov-ovum; ow-oogonial wall.
• Porphyra, popularly known as “nori” in Japan, “laver” in the United
Kingdom, the United States, and Canada, “purple laver” in Britain and
Ireland, “karengo” in New Zealand, “kim” in Korea, and “zicai” in
• It is a common marine red algae found in the intertidal zone on the
• It occurs on both the coasts, Atlantic and Pacific of North America.
• Some species grow attached to the rocks (Lithophytes) and others are
• Porphyra is primarily used as food in the Japanese delicacy “sushi,”
which consists of roasted blades, fish, rice, and other ingredients
• Thallus structure
• The plant body is a plate or sheet like parenchymatous blade apparently
resembling that of a marine algae ulva.
• The margin of the blade can be smooth wavy to greatly convoluted.
• The thallus is often unbranched and attached to the substratum by a small,
basal disc cushion-like holdfast.
• Depending on the species the blade like thallus one to two cells thick.
Frequently it is one cell layer thick.
• Cell structure
• The cells are elongated.
• They are cubical or ellipsoid in form and lie embedded perpendicular to the
thallus surface in the tough gelatinous matrix derived from the cell walls.
• The outer walls of the cells are strongly thickened and covered with cuticle.
The cells are uninucleate. Each cell has a single large axile stellate
chromatophore(Pigment containing cells) with a centrally located pyrenoid.
• In certain species there are two chromatophore in each cell.
• The nucleus lies adjacent to the chromatophore but between the adjacent
• The growth is intercalary.
• It takes place by the division of cells at intervals irrespective of their position.
• It takes place by means of asexual spores formed by direct
transformation of vegetative cells.
• These are known as the neutral spores.
• In sexual reproduction method male and female sex organs are
• Most of the species are dioecious(“double house”) and
• The male sex organ is called as Spermatangia.
• The female sex organ is called as Carpogonia.
• Both are formed from a single vegetative cell.
• Formation of Spermatangia
• They are formed by repeated division of a vegetative cell
• A vegetative cell of the male thallus divides in three planes.
• The first wall is parallel to the surface.
• The daughter cell undergo two vertical divisions.
• Further transverse divisions results in a mass of 32-128 small colourless cells
called as Spermatangia.
• The liberated naked uninucleate protoplast of each spermatangia is called as
spermatagnium. It is a non motile male gamate.
• Formation of Carpogonia
• The carpogonia is formed by slight modification in the vegetative cell of female
• The swallon cell undergoes no division. Its protoplast functions directly as an egg.
• The carpogonium extends to the thallus surface one or both the ends by giving out a
small papillate outgrowth which is considered as rudimentary trichogyne.
• In those sp which don’t have trichogyne, a narrow process occurs containing a thin
stream of cytoplasm.
• It establishes a connection between spermatium and carpogonium.
• Then the spermatatial nucleus migrates through it into the carpogonium to fuse with
• After entering the protoplast divides through meiosis and makes 8-32 uninucleate
haploid meiospore known as carpospores.
• These carpospores are then released and germinated and produced amoeboid cell
and matured to new species.
• The term diatomin is used for the mixture of chlorophyll and carotenoids,
particularly carotene and several brown xanthophylls pigments.
• It is a large group of algae consisting of 200 genera and over 10,000
species, out of which 92 genera and about 569 species are reported from
• The diatoms are the most beautiful microscopic algae due to their
structure and sculpturing of their walls.
• They occur in various habitats like fresh water, saline water and also in
terrestrial condition on or within the soil.
• Sometimes they also occur as epiphytes along with algae, on the leaf of
forest trees, mostly in tropical rain forests.
• Depending on the mode of nutrition they may be photosynthetic
autotrophs or heterotrophs.
i. Discoideae. e.g., Melosira.
ii. Solenoideae. e.g.,
iii. Biddulphioideae e.g.,
iv. Rutilarioideae e.g.,
1. Fragilarioideae e.g., Synedra.
2. Eunotioideae e.g., Eunotia.
3. Achnanthoideae e.g., Cocconeis
4. Naviculoideae e.g., Navicula.
5. Epithemioideae e.g., Epiyhemia.
6. Nitzschioideae e.g., Bacillaria.
7. Surirelloideae e.g., Surirella.
Plant Body Structure of Diatoms
• Plant body is unicellular, generally moves singly. The cells are of
different shapes like round, oval, elongated, rod-shaped, triangular,
• Sometimes they become aggregated and get embedded in a
gelatinous matrix, but they do not behave like multicellular orga-
• In colonial form the cells may be present as uniseriate row (e.g.,
Melosira), like a branched body (e.g., Licmophora flabellate) or other
Cell Structure of Diatoms
• The cell consists of cell wall and protoplast.
• The cells are covered by a siliceous wall, the frustule.
• It consists of two overlapping halves, the theca. The upper one is
epitheca and lower one is hypotheca.
• Both the theca consist of two portions:
• (a) Valve — the upper flattened top and
• (b) Connecting band or cingulum (pl. cingula) — the incurved region.
• The common region of the connecting bands, where both the theca
remain fitted together, is the girdle.
• When the diatoms are observed from the valve side i.e., valve side is
uppermost, called the valve view, but when viewed from the
connecting band, it is the girdle view.
• Depending on symmetry, the cells are divided into two orders:
1. Pennales (bilaterally symmetry)
2. Centrales (radially symmetry).
• In some pinnate diatoms (Cybella cistula, Pinnularia viridis etc.) an
elongated slit is present on their valves, called raphe.
• The raphe is interrupted at its midpoint by thickening of the wall
called central nodule.
• Similar thickening is also present at the ends called polar nodules.
• Some members like Tabellaria fenestrate etc. of the order Pennales,
do not have raphe, called pseudoraphe.
• The cell wall is mainly made up of pectic substances, impregnated
with silica. The content of silica varies from 1% to about 50% on the
basis of dry weight of the cell.
• The entire content present inside the cell wall is the protoplast.
• The cell membrane encloses a large central vacuole surrounded by
• The cytoplasm contains single nucleus, mitochondria, golgi bodies
• The chloroplasts may be of different shapes like stellate, H-shaped,
discoid etc. In some species the chloroplasts contain pyrenoids.
• The photosynthetic pigments are chlorophyll a, c1 and c2, β-carotene,
fucoxanthin, diatoxanthin and diadinoxanthin. The latter two are pre-
sent in small quantity. (The golden-brown colour of diatom cells is
due to the presence of xanthophylls like fucoxanthin, diatoxanthin
• The reserve food of diatoms is chrysolami- narin and oil droplets (they
do not store in the form of starch).
• All diatoms with raphe are motile.
• Most of the members of the order Pennales contain raphe and perform gliding
• The gliding movement is caused by the circulation of cytoplasm within the raphe
by the release of mucilage.
• The rate of movement varies from 02-25 µm/sec.
• The locomotion is affected by temperature, light etc.
• Vegetative reproduction performs with the help of cell division. It
takes place usually at midnight or in the early morning.
• During cell division the protoplast of the cell enlarges slightly.
• Then the protoplast undergoes mitotic division and gets separated
along the longitudinal axis through the median line.
• Now both the theca i.e., epitheca and hypotheca of mother cell
behave as epitheca of the daughter cells.
• Thus new silicious valves are deposited towards the naked sides of
the protoplast and always behave as hypotheca of the daughter cells.
• The pattern of sexual reproduction differs in both orders —
• During this process, auxospore is formed in both the groups.
Auxospore Formation in Pennales
• It takes place through gametic union, autogamy and parthenogenesis.
• These are the types-
1. Production of one auxospores by two conjugating cells.
2. Production of Two Auxospores by Two Conjugating Cells. E.g. Cymbella
lanceolata, Gomphomema parvulum etc.
3. Production of One Auxospore by Autogamy.
4. Production of Auxospore by Parthenogenesis.
5. Production of Auxospore by Oogamy. E.g. Rhabdonema adriaticum
Production of One Auxospore by Autogamy.
• In this process the diploid nucleus undergoes first meiotic division.
Thus two haploid nuclei are formed. The two nuclei in the protoplast
come side by side, fuse together and form diploid (2n) nucleus. This is
called autogamous pairing.
• The protoplast along with diploid (2n) nucleus comes out from the
parent frustule and behaves as an auxospore.
• This is found in Amphora normani.
Production of Auxospore by Oogamy.
In this process the nucleus (2n) of female cell
which behaves as oogonium, undergoes
meiosis and forms four nuclei. The protoplast
is also divided into two unequal parts, each
containing two nuclei.
The lower half is larger and behaves as
functional ovum and the upper smaller one as
non-functional ovum. The functional ovum
contains one functional nucleus and one non-
functional nucleus, which gradually
degenerates at maturity.
• The male cell (2n) behaves as
antheridium, also undergoes meiosis and
forms four nuclei. The protoplast also
divides into two parts. Thus two
microgametes are formed. Each of which
contains two nuclei, of which one is
functional and other is non-functional.
The microgametes are naked, globular
• After coming out, the male gamete
fertilizes the egg and forms the zygote
(2n). Later it functions as an auxospore
and forms new individual of normal size.
It is found in Rhabdonema adriaticum.