Lichens reproduce through both asexual and sexual means. Asexual reproduction occurs through fragmentation of the thallus, or by the formation of specialized structures like soredia, isidia, and cephalodia which break off and form new lichen thalli. Sexual reproduction involves the fusion of male and female nuclei. In most lichens this occurs through ascospores formed within apothecia, while in some it occurs via basidiospores. The life cycle involves spore germination, growth of fungal hyphae which interact with algal cells, and formation of fruiting bodies that produce spores to continue the cycle.
4. 1.FRAGMENTATION
Small fragments of thallus are formed by accidental
breaking or death and decay of the older parts . Each
fragments develops in toa newthallus , provided it
contain algal and fungal component.
Fragmentation is more common among pendent forms,
such as Ramalina reticulate( fish net lichen or lace
lichen)
.
5. 2.ISIDIUM
Isidia are small ,stalked ,
grayish –black coral like
outgrowths which developed
the upper surface of thallus .
The isidium has an outer
cortical layer enclosing the
algal and fungal
components. It is usually
constricted at the base and
easily detachable from the
parent thallus. It germinate
under favourable condition
and form new thallus.
Isidia also help in increasing
the photosynthetic surface
of thallus.
6. SHAPES OF ISIDIUM
Isidia vary in shape and maybe rod like eg:
parmelia, Coral like eg:peltigera, Scale like eg :
collema. Cigar like eg: usnea. (Old Man's Beard, Beard
Lichen, Tree'sDandruff, Woman's Long Hair, or Tree Moss)
7. 3.SOREDIUM
It is the most common method of vegetative
reproduction. These are small bud like outgrowth,
produced on the upper surface by the thallus. They
may either occur within definite pustule-like
compact structures called soralium or may arise so
abundantly as to spread up like a thin grayish layer
of dust. Each soredium consists of a few algae cells
surrounded by a mass of hyphae. The soredia
germinate on suitable substratum and form new
talli.
Eg: Ramalina, Evernia.
10. 4.CEPHALODIUM
These are small wart-like structure formed on the surface of the
tallus. One of the characteristic feature of the cephalodium is that
its algal and fungal components differ from that of the tallus. It is
due to the fact that cephalodia develop on the younger parts of
the tallus from soredia of some other species. Hence, the
cephalodium may be regarded as sterile thallus of some other
lichen.
11. ASEXUAL REPRODUCTION
Lichens reproduce asexually by forming asexual spores
of fungal origin.
ASEXUALSPORES
1.Conidia : In several lichens, the fungal component
forms conidia on conidiophores. Conidia get released
from the lichen and form new fungal mycelia. These
mycelia, in turn, come in contact with suitable algal
components and form new lichens.
12. 2.OIDIA :
These are small and
thin walled bodies,
formed from the
fungal hyphae of
lichens. They get
released from the
parent lichen, come
in contact with
suitable algal
component and form
new lichen plants.
13. 3.PYCNIOSPORES
Pycniospores are produced
inside the structure called
pycnidia. The pycnidia open
into the small pore called
ostiole and a pycnidial wall
made up sterile fungal
hyphae.
The fertile hyphae obstruct
the sexual spores inside the
tips of the pycnidia.
After they fall on the correct
substratum, the
pycnidiospores germinate and
come in contact with suitable
algae. Finally, they develop
into new lichens.
Eg:Physica,Buellia
14. SEXUAL REPRODUCTION
Sexual reproduction is exhibitied only by
mycobiont.
1. In Ascolichen:-
Female sex organ is called Ascogonium.
Basal coiled ascogonium (embedded within algal
layer) and upper elongated multicellular tricogyne
(projects over the surface.)
Male sex organ is called Spermagonia (flask
shaped). It forms male gamete called Spermatia. It
develop close to ascogonia . This enables spermatia
to adhere to the projected part of sticky trichogyne
on dissolution of walls, nucleus of spermatia
migrates to female nucleus and fuse with it.
16. FERTILIZATION
When the growing trichogyne comes in
contact with spermata, fertilization is
effected. The walls of contact dissolve and
the nucleus of the male gamate gradually
passes downward into the oogonium. Then
it fuses with the female nucleus of the egg.
Thus fertilization occurs in lichens.
17. AFTER FERTILIZATION
Several branched ascogenous hyphae form base of fertilized
ascogonium.
Ascogeouns hyphae -> Ascus-> Two nuclei fuse to form diploid
nucleus -> First divide meiotic ally then mitotic ally forming eight
haploid daughter nuclei.
These eight haploid nuclei act as eight ascospore.
Paraphysis is present.
Somatic tissues and paraphysis form fruiting body.
These fruiting bodies are of two types.
1. Apothecium ( Disc shaped ) eg. Parmelia
2. Perithecium(Flask shaped) eg. Dermatocarpon.
Ascopore =>Vary in shapes, size, structure and septation. These are
hyaline.
Ascopore produce hypha, when these hypha found alga, then it form
new lichen.
20. 2. IN BASIDIOLICHEN:-
The sexuality in Basidiolichens is very
much reduced. Sexual phenomenon is
represented only by the fusion of nucleus of
opposite strains to produce basidia. So
Basidiolichens reproduce by basidiospores
produced in basidia. Each basidium bears
four basidiospores at the tip of sterigmata.
