This document summarizes the external and internal structures of Riccia. Externally, the plant body is thalloid and flattened with dichotomous branching. It has scales and rhizoids on the ventral surface. Internally, it has a photosynthetic region on the dorsal side with chloroplast-containing cells, air spaces, and an upper epidermis. The ventral side has a storage region of closely packed cells containing starch and lacking intercellular spaces. Vegetative reproduction occurs through decay and detachment of branches, formation of tubers or adventitious branches, and development of gemmae from rhizoid cells.

1. External and Internal structure of RICCIA
B. Sc. Sem i
Dr. Vasanta I. Kahalkar
Department of Botany
M. G. arts. Science. & late n. p. commerce College,
Armori

2. External Features of Riccia:
• Plant body is thalloid, prostrate, linear or ribbon-
shaped and flattened structure.
• It is dichotomously branched and green to light
green in colour.
• Thallus is thick in the middle and becomes thin
towards the margins.
• An apical notch is present on the terminal portion
of thallus. Plant body has two surfaces, dorsal
and ventral.
• (a) Dorsal Surface:
• A median longitudinal furrow or depression is
present on the dorsal surface.
• Sex organs are also present on this surface.

3. • (b) Ventral Surface:
• Scales and rhizoids are present.
• Scales:
• These are generally present on the margins in
one row or near the growing points.
• Scales are multicellular but one-celled thick
structures.

4. • Rhizoids:
• 1. They are of two types, i.e., smooth-walled
and tuberculate rhizoids.
• 2. Smooth-walled rhizoids are unicellular,
hyaline and fine hair-like structures.
• 3. Tuberculate rhizoids are also unicellular, but
some peg-like ingrowths rise in the lumen of
the cell of these rhizoids.
• 4. Functions of the rhizoids are absorption and
fixation.

6. Internal structure of thallus Riccia:

7. • V. T. S. of thallus, stain in safranin, mount in glycerine and study.
• Following two distinct regions are visible
• (a) Photosynthetic region, and (b) Storage region.
• Photosynthetic Region:
1. It is situated on the upper or dorsal surface of the thallus and
consists of loose green tissue. It is also known as assimilatory
region.
2. It consists of a layer of epidermis, many air pores, air spaces or air
chambers and many one-celled thick vertical rows of chlorophyll-
containing cells.
3. In the cells of vertical rows are present many discoid chloroplasts.
4. In between these vertical rows are present air spaces or air
chambers.
5. Uppermost cells of these vertical rows of chlorophyll-containing
cells remain devoid of chloroplast and thus form a hyaline
discontinuous layer of upper epidermis.
6. Continuity of the upper epidermis is broken by many air pores.

8. • Storage Region:
7. It is situated on the lower or ventral surface of
the thallus and consists of colourless cells.
8. Cells are closely packed and parenchymatous.
9. Cells contain starch and are without intercellular
spaces.
10. The lowermost cells of this region form a
regular lower epidermis, from which arise scales
and rhizoids.
11. Scales are present on the margins of the thallus.
12. Function of storage region is to store the food
material and water.

9. Vegetative Reproduction
• The vegetative reproduction takes place by several
ways.
• By the death and decay of the older parts of the
thallus. Sometimes a part of the thallus,
dichotomously branched decays from the posterior
end and this ways the terminal ends of the
branches remain unaffected which may grow
separately into new thalli.
• By tubers : In some species, the tubers develop at
the apices of the branches of the thallus which face
adverse condition, and develop into new plants on
the approach of favorable conditions.

10. • By adventitious branches: according to Cavers
(1904) in several species of Riccia the
adventitious branches are produced on the
ventral surface of the thallus. These branches
get detached from the thalli and develop into
new gametophytes.
• By gemma formation: According to Campbell
the Riccia may also reproduce vegetatively by
cell division of the young rhizoids which
develop into gemma like structure of the cells.
These structures give rise to new plants.

11. Thank you