This document discusses the vegetative structure of Chlorophyceae (green algae). It describes the many forms their thalli can take, ranging from simple unicellular forms to complex multicellular and parenchymatous forms. Examples are provided of different types of thalli like unicellular, colonial, filamentous, siphonaceous, foliaceous, and heterotrichous forms. The evolution of different thallus types from simpler to more complex forms is also explained. Key structures of green algal cells and various reproductive stages are outlined.

1. Vegetative Structure
Chlorophyceae (Green Algae)
Dr.Mansi Pandey
Dr.Mansi Pandey
Dr.Mansi Pandey 1

2.  Green algae or Chlorophyceae, Division Chlorophyta
 Comprises almost 9,000 to 12,000 species.
 Most green algae occur in fresh water, usually attached to submerged
rocks and wood or as scum on stagnant water; there are also terrestrial
and marine species. Free-floating microscopic species serve as food
and oxygen sources for aquatic organisms. Green algae are also
important in the evolutionary study of plants; the single-celled
Chlamydomonas is considered similar to the ancestral form that
probably gave rise to land plants.
 The photosynthetic pigments (chlorophylls a and b, carotene, and
xanthophyll) are in the same proportions as those in higher plants.
Dr.Mansi Pandey 2

3. Common chlorophytes:
(A) Chlamydomonas sp., (B) Volvox sp., (C) Pandorina sp., (D) Hydrodictyon, (E) Microspora sp.,
(F) Entoderma sp., (G) Coleochaete sp., (H) Oedogonium sp., (K) Struvea sp., and (L) Caulerpa sp.
Green algae, varies in size and shape, include single-celled (Chlamydomonas, desmids),
colonial (Hydrodictyon, Volvox), filamentous (Spirogyra, Cladophora), and tubular
(Actebularia, Caulerpa) forms. Sexual reproduction is common, with gametes that have
two or four flagella.
Dr.Mansi Pandey 3

4. Structure :
 Exhibit a wide range of variations in their thallus structures- Like unicellular
motile (Chlamydomonas), and unicellular non-motile (Chlorella) (Ulva) ),
unbranched (Spirogyra),heterotrichous (Coleochaete), siphonaceous (Vaucheria),
palmelloid (Tetraspora), dendroid (Ecballocystis
 The typical green algal cell- Can be motile or non-motile. Flagella are inserted
either apically or subapically, are one in number, and are of equal size. The anterior
portion of the flagellate cells has an eye spot or stigma that is still inserted on one
side of the chloroplast.
 Eukaryotic cells make up the organism. In most cells, there is only one nucleus,
but the coenocytic bodies of Siphonales and Cladophorales have many nuclei. In
contrast to the normal rule of one nucleolus per nucleus, Conjugales members have
several nucleoli with a central vacuole.
 The protoplast is surrounded by a semipermeable cell membrane that is found
inside the cell wall. Numerous tiny vacuoles in the cytoplasm push the nucleus and
surrounding cytoplasm outward and are known as primordial utricles.
Dr.Mansi Pandey 4

5.  The chloroplast is where the pigments are found - pigments contained in
plastids that vary in shape in different species like discoid, plate-like,
reticulate, cup-molded, winding, or lace formed in various species, and a two-
layered cellulose and pectin cell wall.
 Pyrenoids: Pyrenoid is typically present in chloroplast (s). The greater part of
the individuals has at least one storing body called pyrenoids situated in the
chloroplast where food is stored in the form of starch (proteinaceous cores
within the plastids) also contain proteins other than starch.. Some green
growth might store food as oil drops.
 They generally have a cell wall comprised of an inward layer of cellulose and
an external layer of pectose. Cellulose, which is primarily composed of xylans
and mannans and hydroxyproline glycosides, makes up the majority of the cell
wall. In Chara, calcium and magnesium carbonate are embedded in the cell
wall.
Dr.Mansi Pandey 5

6. Vegetative Structure of Chlorophyceae :-
 Green algae, shows a great variety in their vegetative organization and
also in their life cycle as well as in habitat.
 Organization of thallus ranges from simple, primitive motile unicells, to
complex and highly evolved multicellular forms. They are few microns
to several feet in dimension.
 Habitat Like : Green macroalgae of Ulvophyceous green algae exist in
marine and brackish coastal ecosystems.
Ulva mutabilis (Foliaceous plantbody)
Dr.Mansi Pandey 6

7. From simple to complicated forms, various types of
thallus evolved in green algae along different lines or
according to their habitat.
These are grouped as follows:
 Unicellular (Motile or non-motile)
 Aggregates (Palmelloid or Dendroid)
 Colonial (Motile or Non-motile)
 Filamentous (Unbranched or Branched) [Branched
filaments may be simple, heterotrichous or
pseudoparenchymatous.]
 Siphonaceous,
 Foliaceous, and
 Parenchymatous
Dr.Mansi Pandey 7

8. UNICELLULAR:
Chlorella: Unicellular non-motile green alga, a genus of about thirteen species
of single-celled green algae of the division Chlorophyta. It is spherical in shape,
about 2 to 10 μm in diameter, and is without flagella.
Their chloroplasts contain the green photosynthetic pigments chlorophyll-a and -
b. In ideal conditions cells of Chlorella multiply rapidly, requiring only carbon
dioxide, water, sunlight, and a small amount of minerals to reproduce.
Example of motile unicellular green alga is Chlamydomonas.
Dr.Mansi Pandey 8

9. In another Chlorophyceae, flagella are whiplash type being two in number
or in multiples of two, all being equal in size and attached at the anterior
end e.g. Chlamydomonas or single e.g. Euglena. Euglena is of green algal
origin with several chloroplasts surrounded by three membranes and
phoreceptor pyrenoid.
Dr.Mansi Pandey 9

10. Green algae mostly being aquatic and fresh water
forms show great variety in thallus organization
along with the life cycle and habitat, than any
other group of algae.
From simple to complicated forms, various types
of thallus evolved in different groups of algae
along different lines such as those known as
Volvocine, Coccoid, Siphonaceous or Coenocytic,
Tetrasporine, filamentous (branched and
unbranched), Heterotrichy, Uniaxial / Multiaxial
filaments and Parenchymatous tissue formation.
Dr.Mansi Pandey 10

11.  The most primitive order of Chlorophyceae is
Volvocales. In this group, the simplest and most
primitive thallus is represented by the motile unicells.
 Such unicells could give rise to all other forms of
thalli.
 If the motile unicells loose flagella, the Chlorella type
of thalli could form.
 If the unicells could adhere together loosely, a colony
of simple, similar and unspecialized or specialized
cells could form. The colony could be motile or non-
motile.
Dr.Mansi Pandey 11

12.  Definite number of flagellated unicells could unite
together to form a motile colony. A simple motile
colony may have 4,8,16 or more flagellated unicells,
held by mucilage. All the cells of such a colony are
physiologically independent and each of them
resembles the unicell of Chlamydomonas. The
colony, however, behaves as one unit.
 Gonium has colonies of 4-8-16 cells arranged in a flat
quadrangular plate in a common gelatinous matrix.
Cells are ovoid to pyriform with a single cup-shaped
chloroplast and a pyrenoid.
Dr.Mansi Pandey 12

13.  Each cell of Gonium comprises two equal flagella with
contractile vacuoles at their base and an eyespot. Four and
eight-celled colonies have the flagella on the same side.
 Sixteen-celled colonies have four central cells with their flagella
on the same side with twelve marginal cells with radially
arranged flagella.
16-celled Gonium colony
Dr.Mansi Pandey 13

14.  First line of evolution of green algae into motile
colonies is called the volvocine line. It culminates in
Volvox.
 If the cells in a colony are definite in number,
arrangement and having an anterior, posterior polarity,
the colony is called coenobium, e.g. Gonium, Volvox
and Pandorina-Is like Gonium. It is slightly advanced. It
shows differentiation of cells in anterior end from
posterior end.
Dr.Mansi Pandey 14

15.  A coenobium often gives rise to internal daughter
colonies. In Volvox, the coenobium is spherical and
consist of about 50,000 Chalamydomonas type
biflagellate cells. On maturity, it shows 95%
Chalamydomanas type cells towards the anterior end,
and 10% gonidial cells towards the posterior end of
the colony
Dr.Mansi Pandey 15

16. Dr.Mansi Pandey 16

17. Hydrodictyon sp.
Chlorococcum sp
Non-motile colonies:
The motile cells losing their
flagella and associating together
result into non- motile colonies.
This line of evolution is called
Chloro-coccine line.
A mature colony of the
waternet Hydrodictyon consists
of non-motile elongated cells
make polygonal shapes. These
cells are coenocytic and contain
many nuclei.
Dr.Mansi Pandey 17

18. Siphonaceous or coenocytic thallus: Some single celled
algae elongate to form a nonseptate, multinucleate,
tubular structure. It is called coenocytic condition. It
results from karyokinesis without cytokinesis, e.g. Codium
and Vaucheria.
Vaucheria has a long and branched, coenocytic and
siphonaceous thallus and the septa are formed only at the
time of reproduction or at the site of injury.
Dr.Mansi Pandey 18

19. Acetabularia is a siphonaceous alga, which consists of a
stalk ending in an umbrella shaped cap. The stalk bears
the only nucleus present in thallus. In Caulerpa, a large
coenocytic thallus consists of a branched creeping
rhizome and erect assimilatory shoots of various shapes.
Dr.Mansi Pandey 19

20. Filamentous Thallus: It is formed when the cells are held together
by the production of the middle lamellae after multiple transverse
divisions. Such cases develop when a unicell divides several times
in a single plane. When the cells undergo longitudinal divisions,
the filament branches.
Thus filamentous forms are of two types:
Simple And Branched
Examples:Spirogyra, Ulothrix and Oedogonium.
Spirogyra filaments
Ulothrix filament
Apical Cell
Hold Fast
Oedogonium filaments
Dr.Mansi Pandey 20

21.  Simple filamentous type of thallus consists of a single
row of cells. Spirogyra has the cells arranged from end
to end in a single row or file. It is unbranched with all
cells similar.
 In Ulotrix, the cells are arranged in a single row like
Spirogyra, but it has a rhizoidal cell at the base to get it
attached to the substratum. It has an apical cell too
for division and growth. Oedogonium shows
higher degree of division of labour. It has a rhizoidal cell
for attachment, green vegetative cells for
photosynthesis, cap cells for cell division, and
specialized antheridia and oogonia for reproduction.
Dr.Mansi Pandey 21

22. Branched filament: When a few specialized cells in a
filament divide in a second plane but longitudinally,
branched filament is formed. Such branches arise from
the main axis as lateral outgrowths. In Cladophora, bush
like thallus is formed that attaches to a substratum by
rhizoidal outgrowths arising from the base of the plant
body.
Dr.Mansi Pandey 22

23.  Foliaceous Thallus: A membranous or foliaceous plant
body results if the cells of a filament divide in two
planes simultaneously i.e. transversely and
longitudinally e.g. Ulva.
 Heterotrichous filament: Heterotrichy is presence of
two types of branching. The filament has a prostrate
system and an erect system of branches. It is the most
highly evolved type of thallus organization in green
algae found in the Chaetophorales. The prostrate
system creeps along the substratum and sends rhizoids
to fix the thallus. From it arise the upright filaments at
certain points.
Dr.Mansi Pandey 23

24. In some genera, both the prostrate and the upright
systems are well developed e.g. Stigeoclonium and
Fritschiella. In Coloeochaete, the erect system is reduced
to a few hairs. In Chaetophora, the erect system is more
developed
Coloeochaete
Stigeoclonium
Chaetophora
Dr.Mansi Pandey 24

25. In Fritschiella, the erect system consists of a lower
primary projecting system and an upper secondary
projecting system.
In Draparnaldia, the prostrate system is reduced to the
hold fast. In Draparnaldiopsis, the main branches bear
short and long cells with nodes and internodes
Draparnaldiopsis
Dr.Mansi Pandey 25

26. Large parenchymatous thallus: If the cell divisions in the plant
body do occur regularly in all the 3 planes, a bulky three
dimensional parenchymatous body is formed. The sea weed
Enteromorpha is a common example.
Enteromorpha sp.
Dr.Mansi Pandey 26

27. Zygnematales was earlier kept in Chlorophyceae as an
order but now it belongs to the Zygnematophyceae of
Charophyta. Sexual reproduction is by conjugation such
as in Spirogyra but it represents the most species-rich
algal lineage within the Streptophyta.
Studies using various molecular markers have placed
Charophyta as one of the crown groups in Streptophyta
having a close relationship with land plants.
The Charophytes (including Charales and Zygnematales)
are now kept with the Embryophytes in Streptophyta of
Viridiplantae.
Dr.Mansi Pandey 27