Introduction
Riccia is a simple thalloid liverwort belonging to Bryophyta. It is one of the most primitive bryophytes and is commonly found growing on moist soil, damp rocks, and paddy fields. Because of its simple structure, Riccia is important for understanding the early evolution of land plants.
2. Systematic Position (Classification)
Kingdom: Plantae
Division: Bryophyta
Class: Hepaticopsida (Marchantiopsida)
Order: Marchantiales
Family: Ricciaceae
Genus: Riccia
3. Habitat
Moist and shady places
Damp soil, fields, river banks
Often grows during rainy season
4. External Morphology (Gametophyte)
Plant body: Thalloid, dorsiventral, ribbon-like
Branching: Dichotomous
Colour: Green
Upper surface:
Median groove present
Lacks distinct air pores
Lower surface:
Bears unicellular rhizoids
Scales present only near growing point
5. Internal Structure of Thallus
(a) Photosynthetic Zone
Upper region of thallus
Contains chlorophyll-bearing cells
Air chambers absent or poorly developed
(b) Storage Zone
Lower region
Made of parenchymatous cells
Stores starch-like food
➡ Riccia lacks well-developed air chambers and pores, making it simpler than Marchantia.
6. Rhizoids
Unicellular
Two types:
Smooth rhizoids
Tuberculate rhizoids
Help in anchorage and absorption of water
7. Vegetative Reproduction
Occurs by:
(a) Fragmentation
Thallus breaks into pieces
Each fragment grows into a new plant
(b) Death of Older Parts
Apical portions remain alive
Old central parts die → separation of lobes
❌ Gemma cups absent in Riccia
8. Sexual Reproduction
Oogamous
Usually monoecious (both sex organs on same thallus), sometimes dioecious
(a) Male Sex Organ – Antheridium
Embedded in the thallus
Produces biflagellate antherozoids
(b) Female Sex Organ – Archegonium
Also embedded in the thallus
Produces a single egg
9. Fertilization
Requires water
Antherozoids swim to archegonium
Fusion of gametes → zygote
10. Sporophyte
Highly reduced and simplest among bryophytes
Characteristics
Consists only of a capsule
Foot and seta absent
Capsule remains embedded in gametophyte tissue
11. Capsule Structure
Capsule wall is single-layered
Inside capsule:
Spores (haploid)
Elaters absent (important difference from Marchantia)
12. Spore Dispersal
Capsule wall disintegrates
Spores released passively
13. Life Cycle
Shows alternation of generations
Dominant gametophyte
Sporophyte completely dependent
14. Importance of Riccia
Ecological Importance
Pioneer plant on bare soil
Helps in soil formation
Prevents soil erosion
Academic Importance
Represents primitive liverwort
Used to study reduction of sporophyte
