sporophytic evolution of ferns

1. SPOROPHYTIC EVOLUTION OF
PTERIDOPHYTES
BY ,
BHANUPRIYA R

3. EVOLUTION OF LEAVES
• Pteridophytes exhibit a wide variety of leaf morphologies.
• In fern allies and primitive ferns the leaves are reduced.

4. • In case of true ferns ,leaves are complex and dominant
sporophytic organ.

5. CLASSIFICATION ON THE BASIS OF LEAF
STRUCTURE
MICROPHYLLOUS LEAVES
• One vein
• No axillary branch
• No leaf gaps
• Restricted shape, size
MEGAPHYLLS
• Complex series of veins
• Usually pinnatified
• Leaf trace with leaf gap present
• Diverse shape and size

6. ORIGIN OF LEAVES
General opinion – leaves and branches -modification of the
axis.
Bower – initially the plant was axial –leaves arose- course of
evolution.
Lignier- branches got modified themselves modified into
leaves.

7. THEORIES RELATED WITH EVOLUTION OF
LEAVES IN FERNS
• Most widely accepted two theories are
i) Telome theory [ Zimmermann]- origin of both microphylls
and megaphylls
ii) Enation theory[ Bower]- only the origin of microphylls

8. TELOME THEORY
• Leaves of ferns and seed plants evolved by the
modification of terminal branch of stem.
• Terminal part of dichotomous stem – Telome
• Telome meet each other at the point of forking,
below it is known as- Mesome.
• Telome + Mesome= Telome truss

9. EVOLUTIONARY POCESS IN TELOME
CONCEPT
Overtopping
Reduction
Planation
Syngenesis
Curvation

10. CURVATION

11. CONCEPT OF TELOME THEORY IN GROUPS
1. PSILOPSIDA
Combined pocess of overtopping, reduction and sygenesis result
in the formation of synangium.

12. 2. SPHENOPSIDA
• Recurvation and syngenesis result in a pellate structure with
reflexed sporangia

13. 3.PTEROPSIDA
• Megaphyllous leaves originate by overtopping, planation and webbing.

14. MERITS OF TELOME THEORY
• Explain origin and evolution of sporophytes
• Explain relationship between root, stem and leaves
• Explains phylogenetic relationship between the fossil and the
living plant
• Helps in connecting the living and fossil plants

15. DEMERITS
• Does not explain the whorled or spiral arrangement of
sporangia
• Doen not explain how Telome like structure develop
• Does not provide satisfactory derivation of all leafy stuctures
from branches

16. ENATION THEORY
• Proposed by Bower (1908)
• First step was the outgrowth of protruberance called enation.
• Later enation get increase its size and vascular cylinder of stem
reaches the base.
• Later leaf trace enter the enation .
• This theory explains the origin of microphyllous leaves.

18. SPORANGIA
• Sporangia synangium sporophyll
sporocarp sori strobili

20. Stelar evolution

21. CONCLUSION
• Many workers traced the parallel line of evolution from earliest known
land plants similar to Rhynia with slender, naked and dichotomously
branched with sporangia at terminal.
• This simple axes developed into root, stem and leaves and become
much elaborated and extensive sporophyte during the course of
evolution.
• It is the conspicuous phase in lifecycle , which is how most people
observe the plant in nature

22. THANK
YOU