Riccia is a bryophyte under the order Marchantiales. It has a small thalloid plant body which is not differentiated into root stem and leaves and the plant body is a gametophyte
3. General Characteristics
• Most widely distributed genus of the family
Ricciaceae consisting of 200 species of which 35
are from India
• Named in the honour of P F Ricci.
• Most of the species are terrestrial, which grows
in damp places but, Riccia fluitans is an aquatic
species.
• Examples of a few Indian species are; R.
gangetica, R. discolor, R. himalayensis, R.
glauca, R. crystallina, R. frostii, R. hirsuta, R.
melanospora. , R. kashyapii and R. pandei.
• Plant body shows alternate generation.
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4. Gametophytic Generation
• The plant body of Riccia is gametophytic.
• Thallus is small, flat, dorsiventral, fleshy, prostrate and dichotomously
branched. Dichotomy leads to the rosette like appearance.
• Dorsal surface
Light green in colour.
Thick midrib.
Median longitudinal groove ending in a depression call apical notch.
Growing point situated in apical notch.
• Ventral surface
The ventral surface of thallus bears many scales and rhizoids.
Scales are multicellular and one celled thick structures.
Scales are arranged along the margin in a single row.
Rhizoids are unicellular and un-branched.
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Dorsal groove Apical notch
5. Anatomy of
Gametophytic thallus
• The green photosynthetic region made up of unbranched photosynthetic
filaments separated by narrow air chambers.
• All the cells of the photosynthetic filament except the uppermost one are
isodiametric and possess many chloroplasts.
• Terminal cells are large, hyaline and makes a discontinuous epidermis.
Upper
Photosynthetic
Zone
• This zone lies below the photosynthetic zone.
• It consists of compactly arrangedparenchymatouscells devoid of chloroplast
• Contain starch as reserved food material. The lowermost cell layer of this
zone forms the lower epidermis.
• Some cells extend to form the scales and both types of rhizoids.
Lower Storage
Zone
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6. Scales and Rhizoids
• Rhizoids are of two types:
o Tuberculate – the inner wall layer
modifies into peg-like in growth
which projects into the cell lumen. It
helps in anchorage.
o Smooth walled – both inner and
outer walls are smooth. It helps in
absorption.
• Scales:
o Present on ventral side.
o Two types – simple and ligulate.
o Helps to protect growing point.
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7. Reproduction
1. Vegetative Reproduction
Fragmentation
Death and decay of older portions
Formation of adventitious branches.
Persistent growing apices.
Formation of tubers.
By rhizoids.
2. Sexual reproduction
Sexual reproduction in Riccia is oogamous.
Male reproductive bodies are known as antheridia and female as archegonia.
Some species of Riccia like R. crystallina, R. gangetica, etc. are monoecious or homothallic while other
species like R. frostii, R. discolor, etc. are dioecious or heterothallic.
Antheridia and archegonia remain enclosed with in the antheridial and archegonial chambers and develop on
the dorsal surface of the thallus.
Sex organs develop in acropetal succession.
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8. Antheri
dium
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Antheridum
Basal stalk Oval body
• Short
• Stalk attaches the
antheridium to the
base of the antheridial
chamber.
• It has a flat base with
conical apex.
• A single-layered
sterile jacket encloses
the mass of
androcytes which
metamorphoses into
antherozoids.
• Antheridium is present singly in an antheridial chamber.
10. Dehiscence of Antheridium
• Antheridium dehisce in the presence of water.
• Water enters the antheridial chamber and the sterile apical cells of the
antheridial jacket enlarge by absorbing water and ultimately breaks
open.
• The cell walls form the semifluid content.
• The mature antherozoids along with semifluid mass, come out of the
antheridium to the antheridial chamber and then to the dorsal surface
of the thallus.
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11. Archegonium
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Archegonium
Stalk Neck Venter
• Short
• Helps to
remain
attached to
the thallus.
• Elongated, slender
neck.
• Six vertical rows of
cell enclose 4 – 6
neck canal cells.
• Single layered
ventral wall.
• Single, small
ventral canal
cell.
• Single, large
egg.
12. Fertilization
• The antherozoids released after dehiscence swim on the dorsal surface of the
thallus and reach the mouth of the archegonium.
• The ventral canal cell and neck canal cell disintegrates forming a mucilaginous
mass which absorbs water, swells up and opens the cover cell apart.
• Many antherozoids enter the archegonial neck.
• One of the antherozoid fertilize the egg. Male and female gamete nuclei fuse to
form a diploid zygote.
• This marks the end of gametophytic phase.
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13. Sporophytic Generation
• The mature Sporophyte has a globular capsule embedded within the dorsal
surface of the gametophytic thallus.
• Foot and seta are completely absent.
• The capsule has a single layered capsule jacket and is also covered by a bilayered
calyptra.
• Before sporogenesis, the capsule wall and inner layer of calyptra disintegrates.
• Spores are the first cell of the gametophytic generation. Each spore has 3 wall
layers, namely exosporium, mesosporium & endosporium. They are liberated
after the complete death and decay of the older gametophyte.
• Spores are liberated by wind or rain.
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