The genus Coleochaete is represented by about 10 species, out of which 3 species are found in India. They grow in fresh water either as epiphytes on different angiosperms. They show much variation in their heterotrichous nature. Due to well-developed prostrate system, it forms discoid thailus and looks like pseudo- parenchyma of one cell in thickness.

1. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
Coleochaete
Systematic position
Class: Chlorophyceae
Order: Chaetophorales
Family: Coleochaetaceae
Genus: Coleochaete
Occurrence
 The genus Coleochaete is represented by about 10 species, out of which 3
species are found in India.
 They grow in fresh water either as epiphytes on different angiosperms
Plant Body
 Plant body of Coleochaete is multicellular and heterotrichous in habit (Fig.
3.66A, B).
 They show much variation in their heterotrichous nature.
 Both erect and prostrate systems are well represented in C. pulvinata. But
others may show either well-developed erect system than prostrate system (C.
divergens, C. nitellarum) or prostrate system is well-developed than the erect
one (C. scutata, C. obicularis).
 Due to well-developed prostrate system, it forms discoid thailus and looks like
pseudo- parenchyma of one cell in thickness.
 The discoid thalli may be a circular in C. orbicularis or irregular in C. scutata.

Cell Structure
 The cells are generally hexagonal or polygonal but may be quadrangular in
some region of the thallus.
 The cells of the erect filament of heterotrichous habit are almost cylindrical,
where the length is more than breadth.
 The cells are uninucleate with single large laminate chloroplast generally with
one or rarely with two pyrenoids.

2. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
Reproduction
Coleochaete reproduces both asexually and sexually.
Asexual Reproduction
It takes place by zoospore and aplanospore formation.
Zoospore
 During spring or early summer, asexual reproduction takes place by the
formation of zoospores (fig. 3.67). Any cell of the plant body may function as
zoosporangium (Fig. 3.67A). Each zoosporangium produces single zoospore.
 Zoospores are ovoid, unicellular, uninucleate and biflagellate structure with a
large parietal chloroplast. Eye-spot is absent (Fig. 3.67B).
 The zoospores are liberated from the zoosporangium through a pore on the
sporangial wall (Fig. 3.67A). It loses flagella within a short time and secretes a
wall on the periphery.
Germination
 During germination the zoospore divides either transversely (Fig. 3.67C) or
vertically and with subsequent divisions (Fig. 3.67D) it forms new plant body.
In C. scutata, the first division is transverse .and forms two cells.
 The upper cell forms seta and the lower one divides repeatedly to form discoid
thallus. But in species like C. pulvinata, the first division is vertical and both
the cells undergo repeated division to form a prostrate system. The erect system
develops later from the prostrate system.

3. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
Aplanospore
Aplanospores are formed during unfavourable condition. At that condition, the
zoosporangium, instead of forming zoospore, forms aplanospore. The aplanospores
are non- flagellate, thick-walled and round structure. During favourable condition the
aplanospores germinate and form new thalli.
Sexual Reproduction
The sexual reproduction is highly specialised and oogamous type. The plant body may
be homothallic i.e., monoecious (C. pulvinata) or heterothallic i.e., dioecious (C.
scutata). The male sex organ is called antheridium and female as oogonium or
carpogonium.
Antheridium
• In well-developed heterotrichous form like C. pulvinata, the antheridia are
borne in groups at the apex of erect branches. But in discoid form like C.
scutata the antheridia are developed in the half way between the centre and
periphery of the thallus.
• The antheridium develops as a conical outgrowth of apical cell of the erect
system which is cut off from the mother cell by wall. A number of antheridia
may develop at the apex of a lateral branch (Fig. 3.68A).
• Antheridia may form on the same filament bearing oogonia in homothallic
species. Each antheridium produces single colourless, unicellular, uninucleate,
biflagellate antherozoid (Fig. 3.68B). They are liberated by breaking the apical
side of the antheridial wall.

4. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
Oogonium
The oogonium develops at the apex of an erect branch (Fig. 3.68C). Due to further
growth of the lower cell, the oogonium becomes lateral in position (Fig. 3.68D, E).
The oogonium is a flask-shaped structure with an elongated, colourless receptive
trichogyne (Fig. 3.68E). In discoid species instead of trichogyne, the neck is
represented by small papilla. The basal enlarged portion contains a single oosphere or
egg.
Fertilisation
 Before fertilisation the apex of the trichogyne breaks down (Fig. 3.68F) and
some colourless cytoplasm is exuded out which attracts the antherozoids.
Although many antherozoids get entangled in the exuded cytoplasm, but only
one enters into oogonium and reaches to the egg through broken trichogyne
(Fig. 3.68G).
 Initially the nucleus of antherozoid is smaller in size than egg and after
attaining equal size to the egg, fertilisation takes place resulting in the
formation of zygote or oospore.
Post-Fertilisation Changes
• After fertilization a septum is laid down which separates the basal region from
the trichogyne. Gradually the zygote becomes enlarged and secretes a thick
wall around itself.
• The neighbouring cells of the oogonium get stimulated and form
pseudoparenchymatous covering around it (Fig. 3.69A). The oogonium with
pseudoparenchymatous sheath is called spermocarp. The spermocarp is red or
reddish-brown in colour. It remains dormant throughout the winter.

5. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
• During favourable condition the spermocarp becomes active. The colour of
spermocarp changes to green and then it germinates. During germination its
nucleus undergoes meiotic division. First it divides by a transverse division into
two cells (Fig. 3.69B). This is followed by subsequent division at right angle to
each other and forms octant stage.
• Further divisions make 16-32 celled stage (Fig. 3.69C, D). Each cell with its
protoplast metamorphoses into single biflagellate zoospore (Fig. 3.69E). The
zoospores are liberated by breaking the zygote wall and sheath into two halves.
After liberation the zoospores swim freely for some time. Later on, they germi-
nate and form new haploid plant body of Coleochaete.

6. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
•
•

7. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
Important Features of Coleochaete
1. Plant body is thalloid, multicellular and heterotrichous in habit.
2. Cells are uninucleate with single large lamellate chloroplast generally with one
or rarely two pyrenoids.
3. Asexual reproduction takes place by biflagellate ovoid zoospores and
aplanospores formation.
4. Sexual reproduction is oogamous.
5. The antheridia may be terminal or intercalary. Each antheridium produces single
colourless, unicellular, uninucleate, biflagellate antherozoids.
6. The oogonium is a flask-shaped structure with an elongated neck, the
trichogyne.
7. Each oospore is converted into spermocarp during elaborate post-fertilisation
stages.
8. Oospore undergoes a period of rest and then produces zoospores (16-32) after
meiosis.
9. The zoospores on germination gives rise to new individuals.