Polysiphonia is a marine algae belongs to
Rhodophyceae or red algae.
Polysiphonia is mainly heterothallic. In the life
cycle of Polysiphonia; three kinds of thalli are
found.
(a) The gametophytic thalli which are haploid free
living and dioecious. The male sex organs
spermatangia are formed on male gametophytic
plant and the female sex organs carpogonia are
formed on female gametophytic plant.
(b) The carposporophytes are diploid, dependent
the female gametophyte female plant. They
develop after fertilization from zygote and later
bear carposporangia. The carposporangia form
diploid carpospores.
(c) The tetrasporophytic plant: Free living diploid
plant formed by germination of diploid
carpospores. The plant bears tetrasporangia which
form four haploid tetraspores which give rise to
male and female gametophytic plants.
Totraspore Tetraspore
(o) (n)
Tetraspore
MEIOSIS (n)
Carpo -
spore
(2n)
Female
Male gametophy te gametophyte
(n) Tetrasporophyte (n)
(2n)
Ceropsporangla
and Corpospore
development
(2n)
H
Spermatengial Auxlllary cel Zygote Branch bearing
clusters devolopment (2n) carpogonlum
(2n)
Spermatla
(0)
SEXUAL UNION
Sexual reproduction is oogamous type
and plants are dioecious
The male sex organs is spermatangia or
Antheridia
The female sex organ called as
carpogonium.
The life cycle of Polysiphonia exhibits triphasic
alternation of generation. In the life cycle three
distinct phases occur.
These are:
1.Gametophytic phase.
2. Carposporophyte phase.
3. Tetra sporophyte phase.
Polysiphonia is dioecious plant. The male
gametophytic plants and the female gametophytic
plantsare distinct.
"The fertilization takes place in situ and diploid
zygote nucleus is formed. The zygote develops
in second phase of life cycle, the
carposporophyte is dependent upon female
gametophytic plant. The carporophyte is urn
shaped structure and forms diploid carpospores
in carposporangia.
"The carpospores germinate to make diploid
tetrasporophytic plants. The tetrasporophytic
plant bear tetrasporangia.
" The diploid tetrasporangial nucleus divides
meiotically to form four haploid tetra spores
which again make gametophytic male and
female plants. In life cycle of Polysiphonia; tw
diploid phases carposprophyte and tetra
sporophyte alternate with one haploid
gametophytic phase. Therefore, the life cycle of
Polysiphonia is called as triphasic diplobiontic
with isomorphic alternation of generation.
"Isomorphic alternation of generation: Both
gametophyte and sporophyte are
morphologically similar.
