The "Telome theory" of Walter Zimmermann (1930, 1952) is the most accepted theory that is based on fossil record and synthesizes the major steps in the evolution of vascular plants. It describes how the primitive type of vascular plants developed from Rhynia like plants.

1. Submitted By:
Deepak Das
Roll No
M.Sc. Life Sciences (Specialization in Plant Sciences)

2. Contents
• Introduction
• Meaning of Telome Theory
• Elementary Processes
• Concept of Telome Theory in Evolutionary
processes
• Merits
• Demerits

3. Introduction
Aquatic plants → Land plants
Early vascular land plants
Evolved from
Rhynia
Rhynia

5. • Telome theory was first proposed by –
Walt Zimmermann in 1930
• Based upon : Fossil record
• Evolutionary modification :
 True Leaf
 True Stem
 True Root
 Complex Vascular System
 Protected Sporangia

6. Meaning of Telome Theory
• Telome - “Single nerved ultimate terminal portion of a
dichotomising axis”
• 2 types of Telome:
Fertile Telome – Terminated by Sporangium
Sterile Telome – Without Sporangium
• The connecting axex between two telomes - Mesomes
• Several telomes grouped together to form Telome
truss/Syntelome
• Syntelome:
(i) Phylloid Truss – Only Sterile telomes
(ii) Fertile Truss – Only fertile telomes

7. A figure of Rhyniaceae showing different telomes
Kenrick, P. (2002). The telome theory. Developmental genetics and plant
evolution,

8. Process of Telome Theory
• Rhynia group of plants underwent certain
evolutionary processes
– Overtopping
– Planation
– Syngenesis
– Reduction
– Curvation

9. Overtopping
• One of the two
dichotomising branches
outgrows the other and
become larger and
mechanically stronger
• Larger branch forms –
Axis
• Overtopped branch
forms – lateral branches Overtopping process

10. Planation
Planation Process
• Rearrangement of
telomes and
mesomes from a
three dimensional
pattern to a single
plane

11. Syngenesis
Syngenesis Process
• Telomes and mesomes
fuse tangentially
• Parenchymatous tissue
is developed in between
• Known as webbing
process
• In stem of Selaginella
polystelic condition due
to - simple
parenchymous webbing

12. Reduction
Reduction Process
• Activity of terminal
meristem of each
telome supressed
resulting into much
shorter branches
• Responsible for –
Microphyllous
leaves of lycopsida
and Sphenopsida
Needle like leaves
of conifers

13. Curvation
Recurvation process
• The fertile Telomes
become curved or bend
downwards
• Two sub processes
 Incurvation -
downward shifting of
the sporangia from
terminal or ventral
surface of the leaf in
Pteropsida
 Recurvation -
downward bending of
the sporangia occurs
along with the
sporangial stalks in
Sphenopsida

14. Concept of Telome Theory
Origin of Sporophylls in Lycopsida
• Planation of the fertile and sterile Telomes
• Reduction of the mesomes and in number of
spornagia
• Protolepidodendron and Psilotum – like
axillary sporangia and single veined leaves are
evolved

15. Origin of Sporophylls in Sphenopsida
• Recurvation and Syngenesis processes are
involved
• The intermediate developmental stages are
seen in some fossil genera like Calamophyton,
Hyenia, Protocalamostachys and
Asterocalamites

16. Origin of Sporophylls in Pteropsida
• Overtopping, reduction, syngenesis and
incurvation are the processes involved
• Pinnately-veined sporophylls with marginal
sori developed by the lateral fusion of
mesomes
• In many ferns, the sori are shifted downwards
due to the incurvation process

17. Merits of Telome Theory
• Describes the origin and evolution of
sporophytes of land plants
• Structure of the sporophytes of the most
primitive known plants is defined
• The exact relationship between the root, stem
and leaves
• Connects the living and fossil plants.

18. Demerits of Telome Theory
• Does not explain how a telome-like characteristic
body has been developed [Bower (1935)]
• Telome theory does not explain the whorled or
spiral arrangement of sporangia [Thomas (1950)]
• For origin of Lycopsida, it is somewhat
hypothetical [Andrews (1960)]
• Does not provide an acceptable origin of all leafy
structures
• It does not explain the derivation of the
dictyostelic condition [Stewart (1964)]

19. Reference
• Beerling, D. J., & Fleming, A. J. (2007). Zimmermann's
telome theory of megaphyll leaf evolution: a molecular
and cellular critique. Current opinion in plant
biology, 10(1), 4-12.
• Kenrick, P. (2002). The telome theory. Developmental
genetics and plant evolution, 365-387.
• O.P.Sharma (2016), Series on “Diversity of Microbes
and Cryptogams – Pteridophyta” (pp 28.1-28.5) New
Delhi, India, McGraw Hill Education Pvt. Ltd.
• Vashishta, Sinha, Kumar (2006), Pteridophyta (pp 32-
36) New Delhi, India, S. Chand & Co Pvt. Ltd.