1. Sem. I, Paper I
Associate Prof. Dr. S. A. Gaikwad
Dept. of Botany, V. M. Sangola.
2. Unit 5 : Xanthophyta
Division Xanthophyta- General Characters
1. Div. Xanthophyta -1.Xanthophyceae
1. The cells are eukaryotic in nature.
2. The cell wall is often absent, but when present it contains pectic compounds. Occasionally
cellulose is also present.
3. The motile forms bear usually two flagella but rarely one. They are unequal and inserted at the
anterior end. The flagella are of two types. The larger one is tinsel and the shorter one is whiplash
4. The plastids are yellow-green in colour. The photosynthetic pigments are chlorophyll a,
chlorophyll e, β-carotene and xanthophylls. The chief xanthophyll is diadinoxanthin. The other
xanthophylls are violaxanthin, neoxanthin, flavoxanthin and flavacin. The carotenoids are
normally present in excess amount than chlorophyll. Phycobilins are absent. The pyrenoids are
absent or rarely present. The chromatophores are discoid in shape and are numerous in each cell.
5. The reserve food is oil, lipid and lucosin.
6. Plant reproduces commonly by vegetative and asexual means. Sexual reproduction though
rare, may be isogamous, anisogamous or oogamous.
• The genus Vaucheria (named after J. P. Vaucher) is
represented by 54 species, out of which 9 species are found
• The majority of species are terrestrial and aquatic.
• The terrestrial species grow in winter in the form of green
and thick layer on damp moist soil.
• The aquatic species found mostly in fresh water. A few
species grow in brackish water and some are marine.
5. Structure of Thallus / Filament
• The haploid thallus, i.e., the plant body of Vaucheria, is unicellular,
filamentous, coenocytic and siphonaceous or tubular.
• The filaments are profusely branched and yellowish-green in color.
• The thallus is multinucleate and aseptate (transverse or cross-walls)
showing a coenocytic condition.
• Septa may form during injury or on development of sex organ.
• In terrestrial species the plant body remains attached to the soil
surface with much branched thread like structure, the rhizoid or
branched holdfast called the hapteron. In floating members, the
rhizoids are either absent or not well developed.
7. Cell structure
The thallus structure is differentiated into cell wall and
The cell wall of thallus is thin, weak and non-elastic.
The cell wall is made of two layers, the outer layer is pectic
and the inner layer is made up of cellulose.
Inner to the cell wall there is thick layer of protoplasm.
A very large central vacuole filled with cell sap runs from
one end of the filament to another forming a continuous
canal or siphon.
8. Cell structure
In peripheral part of protoplasm are present a large number of
small oval or disc shaped chloroplasts.
The cytoplasm is present between the vacuole and the cell wall.
The cytoplasm contains numerous circular or disc-like
chloroplasts, nuclei, and chromatophores.
Pyrenoids are usually absent in chloroplasts.
Many nuclei are scattered in the cytoplasm near the vacuole.
The cytoplasm also contains other membrane bound cell
organelle such as mitochondria, small vesicles and food is stored
in the form of oil.
11. a. Vegetative Reproduction
The vegetative reproduction in Vaucheria takes place
It takes place due to accidental breakage of the
vegetative filament into small fragments by mechanical
injury or insect bites.
Septa are formed in the injured region of the filament.
The broken fragments, which are detached from the
thallus, develop into new Vaucheria plants.
12. b. Asexual Reproduction
The asexual reproduction in Vaucheria takes place by the
formation of various types of asexual spores, such as
zoospores, aplanospores, and akinetes.
1. By zoospores
Zoospores are formed singly inside the zoosporangium,
developed at the apical region of the filament.
The entire protoplasm of the zoosporangium contracts to
form oval zoospore. Opposite to each nucleus two flagella
are produced making zoospore a multi-flagellate structure.
13. Structure of Zoospore:
The zoospores are large, yellowish-green, ovoid,
multinucleate and multiflagellate structures, having small
central vacuole and many chromatophores situated
between the vacuole and peripheral nuclei. The paired
flagella are unequal in length. Fritsch (1948) regarded this
kind of zoospore as compound zoospore or synzoospore
as a number of biflagellate zoospores have failed to
separate from one another.
14. Germination of zoospores:
• Before liberation, entire protoplast of the zoosporangium
contracts slightly. During liberation a narrow aperture develops at
the apex through which the zoospore is liberated. Flagella are
formed during liberation.
• The zoospores swim in water for 5-15 minutes and germinate
without undergoing any significant period of rest.
• The zoospores get attached to the substratum, withdraw flagella
and secrete thin walls. The chromatophores move outwards and
nuclei inwards as in vegetative condition.
15. • The two tube like outgrowths develop in opposite directions. One
of the two outgrowths elongates, branches to form colourless
lobed holdfast and the other outgrowth forms yellow-green tubular
16. 2. By Aplanospores
The aplanospores are generally formed by terrestrial species.
Aquatic species form aplanspores under unfavorable condition
The aplanospores are non-motile asexual spores formed in
special structures called aplanosporangia. Aplanospores are
developed singly within aplanosporangium, during unfavorable
Like zoospores, the aplanospores are developed singly inside the
aplanosporangium at the apical side of the aerial hyphae.
During development it also cuts off from rest of the filament by
transverse septum. The aplanosporangium is club-shaped, which
develops single non-flagellate club-shaped or globose
The aplanospore is liberated by rupturing the apical wall. After
liberation the aplanospore germinates into new-filament.
18. 3. By Akinetes
Akinetes are thick walled structures formed during
unfavorable conditions like drought, and low
The akinetes are formed on the terminal part of
lateral branches where protoplasm migrates to the
tips followed by cross-wall formation.
These multinucleate, thick walled segments are
called akinetes or hypnospores.
19. The akinetes by successive divisions
may form numerous thin walled bodies
When many akinetes remain attached to
the parent thallus, the thallus gives the
appearance of another alga Gongrosira.
Hence this stage of Vaucheria is called
During favorable Conditions, the
akinetes and cysts develop into new
20. C. Sexual Reproduction: In Vaucheria sexual reproduction is of
advanced oogamous type. It takes place by antheridium, the male sex
organ and oogonium, the female sex organ. Most of the species are
homothallic or monoecious but a few are heterothallic or dioecious.
Structure of Antheridium: The young antheridium is usually green in
colour. It contains cytoplasm, nuclei and chloroplasts. The mature
antheridia are yellow, may be cylindrical, tubular, straight or strongly
curved. The antheridia may be sessile (without stalk) or with stalk. The
antheridium grows and becomes high curved structured, its upper part is
main antheridium and the lower part is stalk. The nuclei of antheridium
get surrounded by cytoplasm and develop into biflagellate, yellow
colored, spindle shaped many antherozoids. The antherozoids are
21. Structure of Oogonium:
The mature oogonium is a
large globular uninucleate
structure. The nucleus of
oogonium with protoplasm
develops into a single egg.
The oogonium contains
single large, uninucleate
The oogonium secretes a gelatinous drop through a pore near the beak. A large
number of liberated antherozoids stick to the drop. Many antherozoids push into
the oogonium. The antherozoids strike violently, fall back and push forward again
and fall back. Only one antherozoid enters into the oogonium. After its entry the
membrane develops at the pore to stop the further entry of antherozoids. The male
nucleus increases in size and fuses with the egg nucleus to make diploid zygote.
The zygote secretes 3-7 layered wall
around it and is now called as oospore.
The protoplast accumulates oil
droplets. Initially the zygote remains
green, but later it becomes red due to
breakdown of chlorophyll. It remains
within the oogonium and later comes
out by decay of oogonial wall. It
remains dormant for long period which
varies with the duration of
unfavourable condition like high
temperature, desiccation etc.
24. Germination of Zygote (Oospore):
The oospore undergoes a period of rest before
germination. During favourable season the
oogonial wall disintegrates and the oospore is
liberated. The liberated zygote germinates to
form new thallus.
The nucleus (2n) of zygote undergoes first
meiotic division followed by several mitotic
divisions thus forming a coenocytic condition.
The zygote walls cracks at a point and inner
protoplasm elongates, which gradually forms
lower rhizoids and an aerial branch like the
mother Vaucheria plant. The oospore
germinates to make haploid thallus of