This document summarizes the life cycle and reproductive structures of the liverwort Riccia. It describes the alternation of generations between its haploid gametophyte and diploid sporophyte phases. The gametophyte is a small, flat thallus that reproduces sexually through antheridia and archegonia. Fertilization occurs when sperm from the antheridia fertilize eggs in the archegonia, forming a sporophyte. The sporophyte is a simple spore sac that produces haploid spores through meiosis. The spores germinate to form new gametophytes, completing the life cycle.

1. Bryophytes – Alternation of generation, Morphological,
anatomical and reproductive characters of Riccia
Sankrita Gaonkar
Assistant Professor in Botany
sankrita002@gmail.com

2. Contents
• Alternation of generation
• Riccia – morphological, anatomical and reproductive
characters
• References

3. Alternation of generation
Gametophyte:
• Sexual generation – haploid phase (n)
• Bears reproductive organs – antherozoids and eggs
• Gamete fusion – zygote formation – develops into sporophyte
Sporophyte:
• Diploid phase (2n)
• Produce spores – germinate to form gametophyte
• Formation of spores – meiotic division – produce haploid spores
• Involvement of fertilization (syngamy) and meiosis (reduction division) in
gametophytic and sporophytic phases
• Alternation in life cycle in two distinct individuals with different function –
Diplohaplontic life cycle
• Morphologically different generations – Heteromorphic type of alternation of
generation
• Gametophyte  sporophyte  gametophyte

6. Riccia
Classification:
• Class: Hepaticopsida
• Order: Marchantiales
• Family: Ricciaceae
• Genus: Riccia

7. Morphology
Gametophyte:
• Plant body – thallus
• Small, green, flat and fleshy
• Grows prostrate and branches dichotomously –
Rosette form
• Thallus branches called as thallus lobes
• Lobe thickest in middle (midrib) and thins towards
margins
• Upper surface of lobe – median groove or furrow
– dorsal groove
• Rhizoids – simple, unicellular – smooth-walled
and tuberculate

8. Anatomy
• 2 regions: i) photosynthetic
region
ii) storage region
Photosynthetic region:
• Loose, green tissue –
parenchymatous cell with
chloroplast - vertical rows –
function as pseudomesophyll
• Narrow, deep vertical slits
between columns of green
cells – air canals or air
channels
• Uppermost, pear-shaped cell –
pseudoepidermis – have air
pores

9. Storage region:
• Ventral portion of thallus
• Closely packed parenchymatous cells without intercellular spaces
• Contain starch but no chloroplast
• Serve for water and food storage
• Lowermost cells – lower epidermis – rhizoids arise

10. Reproduction:
• Vegetative and sexual reproduction
Vegetative reproduction:
i) Fragmentation
• Depends on ageing of vegetative cells
• Older cells die – young lobes separate
and grow into new thallus
ii) Adventitious branches
• Arise from ventral surface of thallus in
midrib region
iii) Persistence apices
• Occurs in species growing in regions
with long dry periods
iv) Tuber formation
• Apices of thallus lobes become
thickened

11. Sexual reproduction
• Sex organs develop on thallus lobes
• Lie in dorsal furrow or groove –
sunk deeply
• Younger ones at tip and older ones
away
• Antheridia and archegonia - same
thallus (Monoecious), different thalli
(Dioecious)

12. Structure of sex organs
A) Antheridium
• Stands in deep pit – antheridial
chamber – attached to multicellular
stalk
• Narrow pore at tip – ostiole
• Outer sterile jacket layer –
antheridial wall – protection
• Mass of cells - androcyte mother
cells – divides to form 2 sperm cells
– spermatids or androcytes
• Sperm – minute, slender, curved –
pair of whiplash flagella
• Dehiscence – presence of moisture
• Water enters ostiole and antheridial
chamber

13. B) Archegonium
• Flask-shaped
• 2 parts – i) basal swollen portion –
venter, ii) long, slender – neck
• Vertical row of 4 cells – neck canal
cells – surrounded by sterile
protective jacket (neck cells)
• Neck cells – six rows
• Neck tip – 4 large cap or cover cells
• Venter jacket – venter wall – enclose
venter cavity having 2 cells (egg cell
and ventral canal cell)
• Ventral canal cell – function as plug
holding egg cell
• Dehiscence – at maturity, neck cells
and ventral canal cells degenerate –
form mucilage when hydrated

14. Fertilization
• Takes place in presence of water
• Antheridium burst and release
sperms
• Simultaneously, neck canal cells
degenerate – form mucilage
• Cover cells separate from each other
• Sperms enter through archegonial
neck
• One sperm penetrate egg
• Fusion of sperm and egg nucleus
takes place

15. Sporophyte (sporogonium):
• Simplest among liverworts
• Lack foot and seta
• Have a spore sac – single layered wall
• Spore mother cells in spore sac
• 2 layered calyptra
• Mature spores lie free in sac after
break down of sporogonium wall and
inner calyptra layer
• Elaters absent

16. References
• Vashishta BR. 2010. Botany for degree students: Bryophytes.
S. Chand & company ltd.
• Pandey B.P. (2009). Botany for degree students: B.Sc. First
Year. S. Chand & Company Ltd. New Delhi.