Pteridophytes are vascular plants that reproduce via spores. They have a number of shared characteristics including lignified cell walls, tracheary elements, and an independent sporophyte generation. The stele, or central vascular cylinder, of pteridophytes can take several forms. The protostele is the simplest form, with a central xylem core surrounded by phloem. More advanced forms include the siphonostele, with a central pith, and the dictyostele, with overlapping leaf gaps. The eustele features a ring of vascular bundles around the edge of the pith.

1. STELAR
EVOLUTION IN
PTERIDOPHYTES

2. What are PTERIDOPHYTES
O The VASCULSAR CRYPTOGAMS
O An assemblage of seedless vascular plants
that have successfully invaded the land and
reproduce mainly by means of spores

3. Vascular plants together
share a number of apomorphies
O Lignified secondary walls
O Sclerenchyma
O Tracheary elements, cells of xylem tissue
O Sieve elements, cells of phloem tissue
O An endodermis
O An independent, long-lived sporophyte.
O Sporophytic leaves .
O Roots (secondarily lost in the Psilophytes) .

4. STELE
O CENTRAL VASCULAR CYLINDER WITH OR
WITHOUT PITH AND ENDODERMIS
SEPARATING IT FROM CORTEX
pericycle

5. stele
Eustele
Dictyostele
POLYCYCLI
C
SIMPLE
Siphonostele
SOLENOSTE
LE
ECTOPHLOI
C
AMPHIPHLOI
C
SIMPLE
ECTOPHLOIC
AMPHIPHLOI
C
Protostele
POLYSTELE
MIXED
PROTOSTELE
PLECTOSTEL
E
ACTINOSTEL
EHAPLOSTEL
E

6. PROTOSTELE
O The vasculature consists of central core of
xylem completely surrounded by phloem.
O This is the most primitive and simplest of
steles.
O Types of protostele
i)Haplostele
ii)Actinostele
iii)Plectostele
iv)Mixed protostele
v)Polystele

7. i)HAPLOSTELE
O A Protostele with a central core of xylem
surrounded by a layer of phloem.
O e.g. Selaginella stem, Gleichenia
Psilotum
Rhizome T.S

8. ii)Actinostele
O Central xylem core with radiating ribs or a
star shaped appearance surrounded by
phloem e.g. Lycopodium
serratum,Psilotum stem
PSILOTUM
STEM T.S

9. iii)Plectostele
O Xylem is plate like,arranged parallel to
each other and each plate is surrounded
by phloem. e.g. Lycopodium clavatum

10. iv) Mixed Protostele
O Xylem & phloem uniformly distributed
O Xylem elements breakup in to small groups and all
get surrounded by phloem
O Most advanced among protostele and considered
as transitional type between the protosteles and
siphonostele
Lycopodium cernuum

11. V)Polystele
O In Selaginella, the stem axis has several
steles in parallel arrangement.Each stele
is a protostele. eg.some species of
Selaginella

12. SIPHONOSTELE
O Medullated stele (Stele with central pith).
O Pith is surrounded by xyelm and phloem
on the outside.
O Types of siphonostele
i)Simple Siphonostele
ii)Solenostele

13. i)Simple Siphonostele
O Modified protostele with a central pith.
O Central pith is often parenchymatous rarely
sclerenchymatous.
O Types of Simple siphonostele
a)Ectophloic siphonostele
b)Amphiphloic
siphonostele

14. a)Ectophloic siphonostele
O This type of stele has a central pith which is
surrounded by concentric rings of xylem
followed by
phloem.e.g.Osmunda,Botrychium
Osmunda

15. b)Amphiphloic siphonostele
O In this type of stele, the central portion is
occupied by pith.
O Xylem is surrounded both externally and
internally by rings of phloem .e.g.
Adiantum,Marselia
Xylem
Pith
Phloem
Phloem
Marselia
Rhizome
T.S

16. ii)Solenostele
O A siphonostele possess a leaf gap on one point
O It may be a)Ectophloic Solenostele
eg.Osmunda
b)Amphiphloic Solenostele
eg.Adiantum, Marselia rhizome at leaf arising
regions

17. Dictyostele
O Siphonostele with overlapping leaf gaps form
dictyostele.
O The portion of vascular tissue which lies in
between two gaps is termed as meristele.
Each meristele is protostelic in nature.
O Types of Dictyostele
i)Simple Dictyostele- Dictyosteles arranged in
a single ring eg.Polypodium
ii) Polycyclic Dictyostele- Dictyosteles
arranged in two or more rings.A typical stele
possess two or more concentric rings of vascular
tissue e.g.Pteris pteridium Rhizome

18. Polypodium
Pteris pteridium
SIMPLE DICTYOSTELE POLYCYCLIC
DICTYOSTELE

19. EUSTELE
O The vascular system consists of a ring of
collateral, conjoint vascular bundles
situated on the edges of the pith. e.g.
Equisetum