Soral evolution in ferns

1. SORAL EVOLUTION IN FERNS
Presented by…
Sumra Kazbanu A.
M.sc sem – 1 botany
CBO-402
Department of life science
H.N.G.U. Patan

2. CONTENTS:
 Introduction
 Types of sorus & it’s position in ferns
 Shap of indusium
 References

3. INTRODUCTION
Defination of sorus:
The group of sporangia is therefore,called a Sorus.
OR the sporangia usually occur in clusters called
sori or sorus,found on the underside fertile leaves.
 In ferns,these from a yellowish or brownish mass
on the edge or underside of a fertile frond.
 In some species they are protected during
development by a Scale or Film of tissue called the
INDUMISUM.Which forms an umbrella like cover. It
may be unprotected and nacked.

4.  There are some ferns in which the sporangia are nacked
and occur scattered along the veinlets .they do not form
sori.e.g.Leptoteris humenophylloles.
 In Todea burbara the sporangia are densaly scatted and
are not covered by an indusium.the sori in case are ill
defined.

5. TYPES OF SORUS
Depending upon the nature of the sorus and stage of
sporangial development the ferns are divided as:
Simplices, Gradatae and Mixtae.
1.The Simple Sorus: The sporangia in such a sorus
development simultaneously and all of them
mature together.
 All sporangia within a sorus may be at the same
stage of development (Simplices)
 The Simplices are primitive and extend to the
Paleozoic.

6.  In Simplices the size and area of the receptacle is
fixed and only a fixed number of sporangia can be
borne on it with all of them being at the same stage
of development. They mature at the same time. The
number of sporangia per receptacle varies between
10-12. In some cases the sporangia are borne in
two series. E.g.Ophioglossum and Osmunda.

7. 2. THE GRADATE OR BASIPETAL SORUS:
 The Gradatae with an oblique annulus, occupy a middle
position and have been discovered in the Mesozoic.
 In such cases the internal space within the radial
sorus gets filled by overlapping sporangia.
Overcrowding results and there is no space for the
proper dehiscence of sporangia and consequently some
of them do not dehisce. This mechanical inefficiency
can be solved by the elongation of the receptacle on
which the sporangia are borne at different times and are
at different stages of development (Gradatae).
Moreover there is no simultaneous drainage of food by
the developing spores.

8.  The placentae or the receptacles are long and
almost cylindrical.They bear mature or older
sporangia at their distal ends and younger
sporangia near the proximal or basal part.such a
sorus is found in
Dicksonia,Loxosoma,Trichomanes,Cyathea,Als
ophila, etc….

9. 3. THE MIXED SORUS
 Mixtae annulus is present but in a vertical fashion.
 The spores are released in a staggered fashion and
even if the environmental conditions are not
favorable when the spores are initially released; this
problem is solved by a constant crop of spores over
a given length of time.
 This is an evolutionary advanced feature for
survival. The next step in the evolution of the sorus
is the mixed sorus (Mixtae).

10.  Such a sorus is an aggregation of old and young
sporangia that occur mixed and show no regular
arrangement in a sorus.The young and old
sporangia are indiscriminately mixed.such a sorus
is found in majority of the living
ferns.e.g.Polypodiaceae(Adiantum,Pteris,Pteridium,
Davallia)

12. POSITION OF SORUS IN FERNS
 In christensia the sori are nacked,circular and are
irregular arranged between the lateral veins.
 In Maeattia,Angiopteris,Danaea etc…the sori are
elongagated and are situated below the lateral
veins.
 The Ophioglossales are group of interesting ferns
in which the sporangia are marginal in position.

13.  The sporangia in Osmunda
,Davalia,Trivhomanes and many other ferns are
also marginal in position
 In Glecheniaceae, the sporangia from distinct sori
on the ventral surface of the leaves.
 The sori in Mattoniaceae are ventral in position
and are usually arranged in two rows on either side
of the midrib.
 In Adiantum the sporangia developon the
underside of special marginal flaps of lamina that
become reflexed and protect the sorus.

14.  In Marsileales and the Salviniales the sporangia develop
in sori that are borne within distinct structure called the
Sporocarp.
 The sporocarp in Marsilea enclose sori that contain both
micro and megasporongia.
 In Salviniales the smaller sporocarp contain many
microsporangia each and the larger ones contain one or
more megasporangia per sporocarp.

16. INDUSIAL PROTECTION
 Some sori are naked others have an indusium for
the protection of young developing sporangia. The
shape and form of the indusium, method of
attachment are variable. The indusium may be
formed as an epidermal outgrowth covering
receptacle and sporangia (true indusium) or it may
merely be the in turning of the margin of the leaf to
protect the sporangia (pseudo indusium or false
indusium).

17.  The indusium is reniform in Dryopteris,circular in
Polystichum lobatum,funnel shaped in
Davalia,elongated and curved in Asplenium
lanceolatum,Lamaria spicant and Blechnum
occidentale ,In Matteuccia struthiopteris the
indusium is cup shaped with denate margins.

19. REFERENCES
 Botany for degree students;
By:
P.C.Vashishta
A.K.Sinha
Anil Kumar
 Diversity of Microbes and Cryptogams
Pteridophyta
By: prof.S.P.Khullar