This PPT explains about the various views regarding the evolutionary trend among differenr bryophytic plants and their sporophytic structures.

1. Evolution of
Sporophytes in
Bryophytes
Prepared By-
Dr. Sangeeta Das
Assistant Professor
Department of Botany
Bahona College, Jorhat, Assam, India.

2. What is a Sporogonium?
It is the sporophyte of
bryophytes.
It consists of a single, terminal
sporangium with a bulbous
foot and with or without an
unbranched stalk or seta.
The sporogonium is very
delicate, short-lived and
nutritionally dependent on its
gametophyte.

3. Theories of evolution of sporophytes:
There are two contrasting views:
1. Evolution of sporophytes by progressive
sterilization of potential sporogenous tissue
called Theory of Progressive evolution.
2. Evolution of sporophyte due to progressive
reduction or simplification called Theory of
Regressive evolution.

4. Theory of Progressive evolution
Theory of progressive evolution or Theory of
sterilization, was put forward by Bower
(1908-35) and supported by cavers (1910) and
Campbell (1940).
According to this theory, the sporophytes of
complex forms (e.g., Funaria , Sphagnum,
Pogonatum) have evolved due to progressive
sterilization of the potential fertile tissue of the
simpler forms (e.g., Riccia, Marchantia).

5. First Stage:
The increasing sterilisation of sporogenous tissue
from simple sporophyte of Riccia to the most
complex type of Funaria can be arranged through
the following stages:
The simplest known
sporophyte among
Bryophtes is that of
Riccia.
In all species of Riccia,
the sporophyte consists
of only capsule ,there
being no trace of seta
and foot.

6. This stage is seen in Corsinia, belonging to Hepaticopsida,
where a very small sterile foot develops.
The capsule has a single-layered jacket, but inside the
capsule some of the sporogenous cells, instead of forming
spores, form sterile nutritive cells.
Second Stage:
Third Stage:
Further sterilization is seen
in Spharocarpus where the
sporophyte has a sterile
bulbous foot and a narrow
seta, in addition to fertile
capsule.Fig: Mature sporophyte in Sphaerocarpus.

7. This stage is represented by Targionia,
where the sporophyte consists of a sterile
bulbous foot, a sterile narrow seta and a
fertile capsule.
Thus in Targionia, more sterilisation of
sporogenous tissue has been observed.
Fourth Stage:
This stage is illustrated by Marchantia, where further sterilisation of
sporogenous tissue has been noted in comparison with Targionia.
In Marchantia, the sterile tissue consists of a broad foot, a massive
seta, a single-layered jacket of capsule, sterile apical cap at the apex
of capsule and a large number of long elaters with spiral thickening.
Fifth Stage:
Fig: Mature sporophyte in Corsinia.

8. Fig: Evolution of Sporophyte in Bryophytes: A. Riccia sp.; B. Sphaerocarpos sp.; C. Targionia
hypophylla; D. Marchantia polymorpha; E. Pellia epiphylla.

9. Sixth Stage:
This stage is represented by some
members of Jungermanniales like Pellia,
Riccardia, etc.
Here more sterilisation of sporogenous
tissue has been observed.
Sporophyte is differentiated into foot,
seta and capsule having multilayered
jacket.
The sporogenous tissues produce mass of
sterile elatophores and diffused elaters.

10. This stage is illustrated by members of Anthocerotophyta like
Anthoceros.
Here marked reduction in the sporogenous tissue has been noted.
The multilayered capsule differentiates into epidermis with stomata
and chlorophyllous cells.
Seventh Stage:
Eigth Stage (Final Stage):
 The members of Bryopsida like Funaria, Polytrichum,
Pogonatum etc., show the highest degree of sterilisation.
 The sporophyte is differentiated into a foot, a long seta and a
capsule.
 The sterile tissue of capsule consists of the apophysis,
operculum, many- layered jacket, the columella, trabeculae, the
wall of spore sac and the peristome.
 The sporogenous tissue is restricted to the spore sacs only.

11. Fig. : Sporophyte of Anthoceros sp.

12. Fig.: L.S. of mature capsule of Funaria.

13. Thus the sporophyte of Riccia is the simplest
amongst the bryophytes, with a very high
proportion of fertile tissue and the sterile tissue is
very small.
Whereas , the members of the class Bryopsida
(e.g., Funaria, Polytrichum , Pogonatum) have the
most complex sporophyte with a very high degree
of sterility.
The evolution of sporophyte in bryophytes as
such is considered to have taken place by
progressive sterilization of the fertile tissue .

14. Theory of Regressive evolution:
This theory is known as regressive or retrogressive
theory.
It was supported by several scientists like Church
(1919), Kashyap (1919), Goebel (1930) and Evans
(1939).
According to this theory, the simplest sporophyte of
Riccia (comprised of a simple capsule) is the most
advanced type which has been evolved by the
simplification or progressive reduction of the complex
sporophytes mosses (e.g. Funaria, Pogonatum,
Polytrichum, etc.).

15. Stages of progressive reduction:
1. The semiparasitic foliose sporophyte gradually lost its
leaves and became embedded within the gametophyte.
2. Gradual reduction of photosynthetic tissues in the
sporophytes.
3. Restriction or absence of stomata (liverworts) only in the
apophysis region (e.g. Funaria, Polytrichum). In
Sphagnum, the stomata of apophysis are non-functional
and become rudimentary.
4. The capsules of most mosses, hornwort and some
Jungermanniales are multilayered which subsequently
became single-layered (e.g., Marchantia, Riccia, etc.) by
progressive reduction.

16. Along with these changes, there was gradual
elimination of the seta and the foot.
All these changes are accompanied by the
progressive increase in the fertility of the
sporogenous cells.
Evidence from comparative morphology and
experimental genetics support the view that
the simple sporophyte of Riccia is not an
advanced but a reduced structure.