This document discusses the different types of thallus organization found in algae, particularly the Chlorophyceae class. It describes unicellular motile and non-motile forms, multicellular flagellated and non-flagellated colonial forms, plamelloid forms, filamentous forms, heterotrichous forms, and siphonous forms. A wide variety of thallus structures have evolved to allow algae to survive in their environments, with all necessary cellular activities occurring within their thallus organization.

1. Thallus organization on Chlorophyceae
Rashmi M G
1st year MSc. BOTANY
MAHARANI’S SCIENCE COLLEGE FOR WOMEN
MYSORE

2. INTRODUCTION TO ALGAE
1. The algae was derived from a Latin word ‘alga’ meaning
washed away plants on the sea shore or simply sea-weeds
2. Algae are chlorophyll bearing thallophytes in which the
sex organs are either unicellular or multicellular and not
protected by sterile envelope
3. In many unicellular forms, the entire cell acts as gamete
4. If multicellular, the algae may produce many celled sex
organs, and all cells of the sex organs produce gametes
5. There is no sterile cell in the sex organs. However there
are some exceptions
6. That is the male sex organ (antheridium) of Chara is
multicellular and surrounded by layer of sterile cells

3. Some commonly known algae
 Chara
 Diatoms
 Fucus
 Volvox
 Oedogonium
 Nitella
 Ectocarpus
 Sargassum
Oscillatoria
Chlorella
Caulerpa
Vaucheria
Laminaria
Polysiphonia
Chlamydomonas
Ulothrix

4. Phycology
• The study of algae is called algology or
phycology
• The term phycology was derived from Greek
word phycos meaning sea weeds
• The term algae was first introduced by
Linnaeus in 1754 to include a group of
cryptogamic plants, since then the term algae
has been used in botany

5. Salient features of algae
 Algae generally live in aquatic or moist
habitat
 The plant body is a unicellular or
multicellular thallus which is never
differentiated into root, stem and leaves
 Chlorophyll and other pigments are found in
chromatophores present in the thallus,
therefore algae are autotrophic in nutrition
 Starch is the common reserve food in algae

6. Salient features of algae
 The eukaryotic cells may be uninucleate or
multinucleate. Algal cell wall is rich in cellulose.
Some cells are motile due to the presence of
flagella or cilia
 Primitive algae reproduce only by vegetative
methods, but asexual and sexual reproduction
are common in higher forms
 Asexual reproduction takes place by the
formation of motile zoospores
 The sexual reproduction may be isogamous,
anisogamous or oogamous type

7. Fritsch’s system
• F. E. FRITSCH the well known algologist of the
great Britain has published the two volumes of
books on STRUCTURE AND REPRODUCTION
OF THE ALGAE IN 1935-45 and classified the
algae based on pigmentation, details of
flagella, storage food, presence or absence of
true nucleus in cells, range of thallus
structures, methods of reproduction and
patterns of life cycle

8. Fritsch’s system
He divided algae into 11 different
classes
1. CHLOROPHYCEAE
2. XANTHOPHYCEAE
3. CHRYSOPHYCEAE
4. BACILLARIOPHYCEAE
5. CRYPTOPHYCEAE
6. DINOPHYCEAE
7. CHLOROMONADIAE
8. EUGLENEAE
9. PHAEOPHYCEAE
10.RHODOPHYCEAE
11.MYXOPHYCEAE

9. CHLOROPHYCEAE
• The members of Chlorophyceae are otherwise called
green algae
• This class includes 9orders:-
1. Volvocales
2. Chlorococcales
3. Ulothrichales
4. Cladophorales
5. Chaetophorales
6. Oedogoniales
7. Conjugales
8. Siphonales
9. Charales

10. Chlorophyceae
1. These algae have grassy-green chromatophores which contain
chlorophyll a, chlorophyll b, xanthophyll and carotenoids.
2. Storage food- starch and oil
3. Pyrenoids – present in the chromatophores surrounded by starch
sheath
4. Cell wall- cellulose
5. Flagella -2 or 4 equal in length if motile
6. Sexual reproduction- isogamy, anisogamy, oogamy
7. Thallus- may be unicellular or multicellular; if multicellular, it may
be filamentous or heterotrichous or siphonous or pseudo-
parenchymatous
8. Many species are haploid but some are diploid
9. They are common in freshwater than in salt water
10. Ex. Chlamydomonas, Volvox, Chlorella, Oedogonium, Caulerpa,
Coleochaete etc

11. Thallus organization
• There exist a wide variety of thalli in algae,
particularly in vegetative plant body
• The different forms show a definite range.
• On the other hand there are simple plants where
the thallus body is microscopic and consists of
only one single cell (Chlamydomonas)
• All the morphological structures and cytological,
physiological, genetical and other vital and
necessary activities go on regularly in that single
cell only

12. Thallus organization
• Some of the algae are very large (sometimes 60m or more) and
very complex type of plant body is some Chlorophyceae and many
Phaeophyceae and Rhodophyceae that becomes completely a
parenchymatous organization (Ulva, Porphyra, Laminaria,
Macrocystic, Nereocystis) resembling superficially with that of an
angiospermic plant
• There are intermediate stages also like
• colonial (Volvox)
• palmelloid (Tetraspora)
• dendroid (Prasinocladus)
• coccoid (chlorella)
• filamentous (Spirogyra, Ulothrix, Oedogonium, Cladophora,
Pithophora)
• heterotrichous (Fritschiella)
• siphonous (Vaucheria)
• uniaxial (Batrachospermum)
• multiaxial (Nemalion, Polysiphonia)

13. UNICELLULAR MOTILE FORMS
• Unicellular motile forms are found in all
major groups except Phaeophyceae,
Rhodophyceae, Bacillariophyceae and
Myxophyceae
• The distinguishing features are the
presence of a unicellular plant body
bearing means of motility i.e. flagella
• The most common example is
Chlamydomonas in which the
biflagellate plant body is surrounded
with a definite cell wall, enclosing a
cup-shaped chloroplast, one or more
pyrenoids,2 contractile vacuoles, an
eyespot besides other cell organelles
and a nucleus

14. UNICELLULAR NON MOTILE FORMS
• It is seen in algal groups of
Chlorophyceae,
Chrysophyceae,Cyanophyce
ae, Xanthophyceae,
Bacillariophyceae and
Rhodophyceae
• They posses unicellular
plant body with no flagella.
The most common example
is Chlorella which possesses
microscopic spherical cells,
each with a nucleus and cup
shaped chloroplast

15. MULTICELLULAR FLAGELLATED
FORMS/ COLONIAL FORMS
• These are colonial members of algae whose
cells bear the means of motility i.e. flagella
• Innumerable numbers of cells are present
in the colony. A colony with definite
number of cells and having a constant
shape and size is called coenobium
• Multicellular motile forms are found in
many genera of Chlorophyceae,
Chrysophyceae, Dinophyceae
• The most common example of such forms
is Volvox in which a definite number of
cells (500-50000) are interconnected with
each other with the help of protoplasmic
connections
• The coenobium is hollow and spherical and
contain a single layer of cells arranged on
the periphery
• All cells are chlamydomonad in structure

16. MULTICELLULAR NON FLAGELLATE
FORMS /NON FLAGELLATED COLONIES
• In this form the algae bear a
definite number of cells and
thus represent a coenobium
• The cells are non motile and do
not have flagella or any other
means of motility
• The cells of the net remain
connected in the form of
groups of 5/6 forming
pentagonal or hexagonal
structures . This is seen in
Pediastrum
• This must have been
developed by the aggregation
of unicellular non-motile cells

17. PLAMELLOID FORMS
• In this form the algae in which non
motile cells remain embedded in an
amorphous gelatinous/ mucilaginous
matrix
• The cells are aggregated within a
common mucilaginous envelope. All
the cells are quite independent of
one another and fulfill all functions
of an individual
• In Chlamydomonas the cells loose
their flagella, undergo successive
divisions and form 8/16 or more
cells which simultaneously get
surrounded by a mucilage
• On coming over of favorable
conditions mucilage gets dissolved
and all the cells are set free

18. FILAMENTOUS FORMS
• Many cells arranged one upon the
other in a definite sequence,
uniseriate row, constitute filament
• The filaments may be branched or
unbranched in different algal
members
• Unbranched filaments are found in
algae like Spirogyra, Ulothrix,
Oedogonium, Oscillatoria, Spirulina,
Anabaena
• Branched filaments are found in
Cladophora, bulbochaete etc

19. HETEROTRICHOUS FORMS
• Hetero means different and
trichous denotes trichome
or filament
• In this form the algal plant
body is very much evolved
and consists of more than
one type of filaments and
thus represents the
heterotrichous habit
• It is one of the characteristic
feature of Chaetophorales of
Chlorophyceae
• Ex, Fritschiella tuberosa

20. SIPHONOUS FORM
• In this form the plant body
enlarges without the
formation of any septa
• Because of the presence
of many nuclei, such an
organization of plant body
is a coenocyte
• A large central siphon-like
vacuole is present in the
thallus and thus the name
siphonous
• Ex. Vaucheria

21. CONCLUSION
• A wide range of thallus are observed in algal groups
which are developed and evolved to sustain in the
external environment where they live
• All the morphological structures and cytological,
physiological, genetical and other vital and necessary
activities go on regularly in their forms
Reference
https://www.wikipedia.org/
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Diversity of microbes and cryptogams by O P SHARMA, MAC GRAW HILL EDUCATION