This document discusses the morphology, anatomy, and reproduction of Marchantia, a genus of liverwort. It belongs to the division Bryophyta, class Hepaticopsida. Marchantia has a dorsiventral gametophyte generation that reproduces sexually or asexually. Sexual reproduction involves antheridiophores bearing antheridia that produce sperm, and archegoniophores bearing archegonia containing eggs. Fertilization forms a sporophyte generation consisting of a foot, seta, and capsule containing spores. The spores germinate to form a new gametophyte generation.
3. Habitat and Distribution
ā¢ Genus has about 65 species
ā¢ Grows best in cool, moist and shady places
ā¢ Marchantia polymorpha grows as a pioneer in burnt forest soil
Distribution in India:
ā¢ 11 species occur in India mainly in western Himalayas
ā¢ M.polymorpha occurs at high altitudes in Himalayas on moist river banks
and rocks
ā¢ M.palmate occurs in Kashmir, Kumaon, South India, Bengal and Assam
ā¢ M.simlana occurs in Himachal Pradesh
ā¢ M.nepalensis in Punjab and in Garhwal & Kumaon hills
5. Dorsal Surface:
ā¢ A shallow groove marked by the presence
of a distinct midrib in each branch
ā¢ Many polygonal areas which demarcate
the outline of underlying air chambers
ā¢ Each polygonal area has a pore in its
centre called air pore
ā¢ Gemma cups are present along the midrib
ā¢ Each branch has a growing point situated
at the apex in a groove called apical notch
7. Rhizoids
ā¢ Unicellular and colourless
ā¢ Two types
i. Smooth walled- Inner walls are
smooth
ii. Tuberculate- Inner walls show papilla
like outgrowths
ā¢ Functionā Anchorage and absorption of
water and minerals
Optical Section
8. Scales
ā¢ Multicellular(one cell in thickness) and violet
coloured due to presence of anthocyanin
pigments
ā¢ Arranged in 2 rows on either side of mid-rib
ā¢ Two types
i. Appendiculateā these have an apical sub-rotund
appendage and from inner row of
scales
ii. Ligulateā these are small, without
appendage and form outer row of scales
ā¢ FunctionāProtection of growing point and
retention of water by capillary action
Appendage
Appendiculate Scale
Ligulate scale
9. Anatomy
Air Pores
ļ±A cross-section of thallus shows shows 3 distinct regions:
(i) Epidermal region (ii) Photosynthetic region (iii) Storage region
ļ Barrel shaped
ļ Each pore has 4-8 superimposed
tiers of cells
Epidermal Region
ā¢ Includes upper and lower epidermis
ā¢ Upper epidermis forms protective covering
over photosynthetic region
ā¢ Has many air pores that open internally into
air chambers
ā¢ Lower epidermis forms lowermost layer of
thallus
ā¢ Cells of lower epidermis give rise to rhizoids
ļ Each tier consist of a ring of 4-5 cells
ļ The cells of lowermost tier project
inward giving the pore a star-shaped
appearance
ļ Half of tiers project outward and half
project inward
ļ The pores have comparatively wide pore
passage in the middle than on margins
ļ These are analogous to stomata but they
cannot control the pore size like stomata
10. Anatomy
Photosynthetic region
ā¢ Lies below upper epidermis
ā¢ It consists of large air chambers
separated by single layered partition wall
ā¢ Uniform in shape and are arranged in a
horizontal row
ā¢ Many photosynthetic filaments arise
from foot of each chamber
ā¢ The filaments are made of chloroplast
containing cells
11. Storage region
ā¢ Lies below photosynthetic region
ā¢ Compact zone of several layers of polygonal
parenchymatous cells
ā¢ Cells devoid of chloroplast and no intercellular
spaces in between
ā¢ Cells contain starch and protein granules
ā¢ Mucilage and oil containing cells are also present
ā¢ Storage region thick in the centre and tapers
towards the margins
ā¢ Cells of midrib region are elongated and with
reticulate thickenings
Anatomy
12. Reproduction
Vegetative reproduction:
By progressive death and decay
ā¢ Mature cells are present at posterior end and are short-lived
ā¢ New cells are regularly formed by apical cell
ā¢ Death and decay therefore naturally starts from the posterior end
ā¢ As the process of decay reaches the point of dichotomy, two apical
parts of thallus separate
ā¢ Each grows into a new plant
13. Reproduction
By adventitious branches
ā¢ Some species possess adventitious branches on ventral
surface
ā¢ On separation these grow into new thalli
14. Reproduction
By Gemma
ā¢ Gemma cups(2mm X 3mm) are cupules
present on dorsal surface along midrib
region
ā¢ Margins are hyaline, lobed, spiny or entire
ā¢ From floor of gemma cup many small,
stalked, discoid & biconvex gemma arise
ā¢ Gemma is constricted in middle and 2
notches possess a row of apical cells
ā¢ Gemma contains chloroplast containing
cells and rhizoidal cells
ā¢ Some mucilage hairs also arise from
gemma cupās floor which imbibe water and
help in deispersal of gemmae
ā¢ Gemmae on coming in contact with ground
start germinating immediately
15. Sexual Reproduction
ā¢ Marchantia is a heterothallic or dioecious plant
ā¢ Male thallus bears antheridiophores and female thallus bears
archegoniophores
ā¢ They arise from distal end of thallus from growing point and
after their formation growth of thallus ceases
16. Antheridiophore
ā¢ It has 1-3cm long stalk that bears 8 lobed peltate
disc
ā¢ Inner structure similar to that of thallus with
upper epidermis(having air pores), air
chambers(having photosynthetic filaments)
ā¢ Antheridial chambers alternate with air chambers
ā¢ Each antheridial chamber contains a single
antheridium and opens externally by a pore
called ostiole.
ā¢ On each lobe antheridia arise acropetally
ā¢ Antheridiophore has 2 longitudinal grooves which
contain rhizoids and scales
17. Antheridium
ā¢ A mature antheridium is globular or oval with
multicellular stalk
ā¢ Body of antheridium has a single layered sterile jacket
enclosing androcytes which eventually metamorphose
into antherozoids
ā¢ The antherozoid is a minute biflagellate structure
Dehiscence of antheridium:
ā¢ Water enters the antheridial chamber through ostiole
ā¢ Some cells at the distal end disintegrate when they
come in contact with water and hence antheridium
ruptures
ā¢ Antherozoids come out of ostiole like smoke column and
spread on surface of antheridial disc
18. Archegoniophore
ā¢ It has slightly longer stalk(2-5cm) and a
terminal disc which is 8 lobed
ā¢ Archegonia are borne on dorsal surface in
acropetal succession
ā¢ Internal structure is similar to thallus with
upper epidermis having air pores and
underlying air chambers
19. Archegonium
ā¢ The archegonium is a stalked flask shaped
structure with a basal swollen venter and an
elongated neck
ā¢ Venter is surrounded by 1 celled thick sterile
jacket and contains a large egg cell and relatively
small venter canal cell
ā¢ The neck consist of 6 vertical rows of cells called
neck cells which enclose 4-8 neck canal cells
ā¢ Tip of neck has a rosette of 4 cover cells
20. Fertilization
ā¢ Water is essential for fertilization
ā¢ Archegonia are placed upright on archegonial disc
ā¢ Venter canal and neck canal cells degenerate to form
a mucilaginous substance which imbibes water and
results in sparation of cover cells by pressure
ā¢ Antherozoid present on surface of antheridial disc are
splashed by rain drops on to the surface of
archegonial disc
ā¢ They are attracted chemotactically towards the neck
of archegonium
ā¢ Antherozoids enter archegonium and only one fuses
with egg leading to formation of zygote
21. Post fertilization events
(Inversion of Archegonia)
ā¢ After fertilization, archegoniophore elongates
accompanied by rapid growth of central part of
archegonial disc that leads to inversion of archegonia
ā¢ The arrangement of archegonia is also reversed from
acropetal to basipetal
ā¢ This process of inversion is accompanied by
development of one cell thick tissue called perichaetium
or involucre on both sides of each archegonial row
ā¢ Also long, green, finger-like projections arise from
margins of disc known as Rays
22. Sporophyte
ā¢ Zygote develops to form sporophyte
ā¢ It is differentiated into foot, seta and capsule
ā¢ Foot-It is basal bulbous part which anchors and
provides nutrition to sporophyte
ā¢ Seta-It is short stalk that connects foot to
capsule
ā¢ Capsule-It is yellow coloured oval structure and
has a single layered jacket
ā¢ In young sporophyte, capsule encloses
sporogenous mass which differentiate into
spore mother cells and elater mother cells
23. Sporophyte
ā¢ Spore mother cells give rise to spore tetrad by meiosis
and elater mother cells give rise to elaters which are
diploid and sterile
ā¢ During the development of sporophyte from zygote,
the venter wall cells give rise to 2-3 layered protective
covering of sporophyte called calyptra
ā¢ The basal cells of archegonium give rise to one celled
thick collar like outgrowth outside the calyptra called
Perigynium or Pseudoperianth
ā¢ Towards maturity of sporophyte, the seta elongates
and pushes the mature capsule out through calyptra,
perigynium and perichaetium
24. Dehiscence of sporophyte
ā¢ Single layered capsule wall splits into a no. of
longitudinal valves which extend from apex towards
the middle of capsule
ā¢ The valves are rolled back due to annular thickenings
in jacket cells
ā¢ Jerky movement of elaters due to their hygroscopic
nature leads to loosening up of spore mass and
scattering of spores in air
25. Germination of Spores
ā¢ Spores are viable for about a year
ā¢ Under favourable conditions they absorb moisture from substratum and increase
in size
ā¢ Chloroplasts reappear at this stage
ā¢ Spore undergoes repeated divisions to form 6-8 celled filamentous structure with
a rhizoid at one end
ā¢ The apical cell cuts off derivatives on lateral sides and finally give rise to
gametophyte
26. References
ļ¼P.C. Vashistha Bryophytes S. Chand, Delhi, India
ļ¼A Textbook of Botany-- Singh, Pande and Jain
ļ¼Bendre and KumarāPractical Botany Vol.1
ļ¼en.wikipedia.org/wiki/Marchantia
ļ¼www.google.co.in/marchantiaimages