GYMNOSPERMS .pdf pentoxylales, pteridospermales, caytoniales, cycadeodales, glossopteridales

This slide explains about five fossil species of gymnosperms

1. Pteridospermales, Glossopteridales,
Caytoniales, Cycadaeoidales,
Pentoxylales

2. PTERIDOSPERMALES
•They are also known as seed ferns.
•They bore fern like foliage, which in turn bore seeds that were
unprotected.
•It is a very large order that includes a heterogenous assemblage of tree
like or sprawling plants.
•They came into existence during Upper Devonian and lived through
Carboniferous and Permian period and reached their climax in
Mesozoic era.
•This group was discovered by Grand Eury in 1877.

4. General characteristics
•The plants have erected, slender, or weak stems.
•The leaves are large, pinnately compound and frond-like.
•The leaves have resistant cuticle.
• Secondary wood and phloem were formed in smaller amounts.
• Secondary wood was manoxylic.
• The tracheids of secondary wood bear multiseriate bordered pits.
•The seeds are not borne in cones or inflorescences, but are directly
borne on modified or unmodified foliage.

5. Reproductive structures
•Seeds are produces directly on the foliage.
• Microsporangium contain branches. It can be monolete or trilete.
•Megaspore had a very thick wall.
• Ovules and seeds lack annulus and contain cupule like structures.
•It contain integument, pollen chamber and micropyle.
• Seeds can have single or double vascular system is present.
•Male gametes are motile and discharged directly into pollen chamber.
•It germinate by a number of peripheral cells enclosing the central
cavity.

6. Similarity with Pteridophytes
•The leaves are large and pinnately compound.
•The lateral veins branch dichotomously.
• Polystelic condition: It is also characteristic of some ferns.
•The microspores are trilete like the pteridophytic spores.
• The spermatozoids are motile and multiflagellate.

7. Similarity with Cycadophytes
•The stems are aerial and erect and bear pinnate compound leaves.
• The leaf traces are mesarch.
•The leaf traces arise mostly by tangential divisions.
• The leaf traces in Medullosaceae and Cycadales are multiple.
•Microspores of some Medullosaceae and all Cycadales are monolete.

9. GLOSSOPTERIDALES
•Glossopteridales were an extinct order of seed ferns.
•They were found in Gondwana (South America, Africa, Antarctica,
Australia, India).
•Their leaves are spatulate and tongue shaped (glossa: tongue).
•Seeds are produced on fertile leaves.
•It is found during upper Silurian period.
•It shows characters of both angiosperms and gymnosperms.

11. Similarity with angiosperms
• Fertilization by pollination.
•Presence of microspongia.
• The structure similar to typical angiosperm pollen tube observed in
Glossopteridales.
•In angiosperms a closed carpel provides an added protection against
predation, parallel to this Glossopterideles also have the same
tendency to protect their ovules.
• Their fruitification link cycadofilicales to angiosperms rather to
gymnosperms.
•Plumstead suggest that Glossopteris is the ancestors of flowering
plants.

12. Similarity with gymnosperms
•Occurrence of simple leaves covered with resistant cuticle.
•Structure and arrangement of stomata.
•Presence of gymnosperms type lignin lamellae in their stomata.
•Structure of primary and secondary xylem in Vertibraria (stem).
•Seeds are naked.
•Structure of ovule is Gymnospermic in all character.
•Some fruitifications are bisexual.

13. Caytoniales
•These groups are present during Upper Triassic to the lower
cretaceous.
• It is not fully discovered so, we know only a little about the stem
fragments and nothing about the roots, gametophytes and embryos
etc.
•The available fossils are in the form of compressions hence
anatomical and histological details are scanty.
•it is not possible to form an idea about the entire plant.
•Several authors compare the individual organs with other groups.

15. General characteristics
•It consist of a slender petiole and distinct midrib.
•Its megasporophyll consist of dorsiventral rachis, which is stalked and
swollen at tips.
•It shows oval scars.
•Seeds are ovoid and orthotropous.
•Pollen grains are unicellular and winged.
•Ovules have an apical tubelike structure called the micropylar canal.

16. PHYLOGENETIC RELATIONSHIP
•Caytonia was discovered by Hamshaw Thomson.
• According to him he mistakenly thought that the entire ovule is
enclosed in the cupule.
•He conducted many experiments and concluded that the fruit contain a
stigma with a funnel shaped opening to lodge the pollen grains.
•The entire pollen grains cannot enter into the ovule which is a
characteristic feature of angiosperm.
•This idea was later on disapproved by Tom Harris.

17. Cycadaeoidales
•This order is also called Bennettitales, which is a fossil group.
•It is flourished well during Triassic period.
•It is found as sandstone cast in Great Britain.
•They are entirely extinct and resembled cycads in apical crown of
large pinnate compound.
•They were fossilised either in the form of compressions or in petrified
form.

19. General characters:
•Stems are of conical shape and grow up to several meters.
•They grow very slowly and branch profusely.
•The venation is unicostate parallel.
•The stomata are syndetocheilic ( two guard cells arise from a single
mother cell).
•The reproductive organs are bisexual (Cycadroiden, Williamsoniella)
in majority of the peers but unisexual condition (Wirlandiella
angustifolia) is not rare.
•The flowers consists of a basal aggregation microsporophylls
surrounded by a receptacle that may be flattened or dome-shaped.

20. •The flowers arise in the axils of leaves in all the Bennettitales.
•The ovales and seeds are stalked (Cycadeoidea. Williamsonia)
Wantsoniella) or sessile.
•The flowers are surrounded by numerous hairy bracts that arise
from the base of the receptacle.
•Cupule is not present.
•Pollen arise in whorls and are borne in bilocular synangia that
maybe a sessile or stalked.
•The seed possess two cotyledons.

21. Resemblances with pteridospermales
• Presence of ramental hairs.
•Internal structure similar.
•Both having syndetocheilic stomata.
•Digest leaf trace.
•Microsporophyll bearing synangia and presence of cupule.

22. PENTOXYALES
•The name Petoxylales was proposed by Prof. Bishal Sahni in the year
1948.
•They have been found to occur in silicified petrification.
•The plants were probably shrubs or small trees. The habit is not known
but the size and diameter of the stem, its branching and leaves reflect
upon its shrubby or tree-like.
•It shows the combination features of Bennetitales, Cycadales,
Coniferales.

23. General characters:
•The branches were of two types:
(1) long shoots and (1) dwarf shoot.
•The leaves were spirally arranged.
• The stems were polystelic with 5 & 6 primary steles, hence the name
Pentoxylales. Each stele has its own complete ring of cambium.
•The development of secondary wood is exocentric.
•The secondary medullary rays were uniseriate.
•The leaves were simple, lanceolate and thick. The venation was open,
rarely reticulate.

24. •The reproductive organs were unisexual. The female strobili looked
like blueberries.
• The male organs consist of a short of branched sporangiophores
fused at the base into a disc.
•The sporangiophores bear microsporangia on its short branches.
• The reproductive organs are borne terminally on short branches.
• The tracheids have crowded circular bordered pits on their radial
walls.
•The female reproductive organs consist of a thick central axis with
ovules attached to it in a spiral manner.
•The ovules were sessile.

25. Cycadalian characters
•Tree like habit.
•Leaf traces are diploxylic.
•Unisexual reproductive organs.
•Microsporangia not in synangia with monocolpate boat shaped
microspores.

26. Characters of Bennettitales
•Whorled arrangement of microsporangiophores.
•Bisymmetrical ovule.
•Thick sclorotesta.
•Pentoxylales differ from cycadeoidales in having polistelic stem and
lack of intersemilnal scales between ovules.

27. Resemblance of Pentoxylales with Angiosperms
•Both pentoxylon and Pandanus are erect or sub erect.
•Both are dioecious.

28. THANKYOU