The document summarizes the Pentoxylales order of fossil plants. Some key points:
- Pentoxylales were first proposed in 1948 and included plant fossils found in India and New Zealand consisting of stems, leaves, pollen organs, and seed organs.
- The plants were likely shrubs or small trees with multi-stemmed trunks bearing spirally arranged leaves.
- Anatomically, the stems had 5-6 vascular bundles and thick, compact wood resembling conifers. Leaves had two zones of xylem and both syndetocheilic and haplocheilic stomata.
- Reproduction involved unisexual cones, with
2. Pteridospermales (seed ferns),Aiswaria Raj,St.Mary’s College
PENTOXYLALES
The name was proposed by Prof. Birbal Sahini in the year
1948 for a group of fossil plants.
Distribution- Rajmahal hills [Bihar] of India & from New
Zealand.
The order includes - number of stems [Pentoxylon and
Nipanioxylon ], Leaves [Nipaniophyllum].
Pollen bearing organs [ Sahnia ].
Seed bearing organs [ Carnoconites ].
3. Pteridospermales (seed ferns),Aiswaria Raj,St.Mary’s College
MORPHOLOGY
The plants were probably shrubs or small trees.
The stems were 3 mm to 2 cm long. It bore rhomboidal leaf
scars & spirally arranged leaf.
The branches were of two types-
Long shoots
Dwarf shoot
5. Pteridospermales (seed ferns),Aiswaria Raj,St.Mary’s College
ANATOMY
The stem were polystelic with 5&6 primary steles hence the
name pentoxyleae.
Each stele have it’s own cambium, it produced more
secondary tissue towards center so that secondary wood became
exocentric.
The secondary xylem was pycnoxylic, ie; the wood was very
compact.
The secondary wood shows growth rings but it cannot be
definitely stated whether they represent annual rings.
7. Pteridospermales (seed ferns),Aiswaria Raj,St.Mary’s College
In the leaf anatomy it has diploxylic condition ie; two
distinct regions of xylem one centripetal & the other is
centrifugal.
The stomata were regarded by Sahni to be syndetocheilic but
later Vishnu Mitter found that haplocheilic or cycadalean
stomata also occur.
Syndetocheilic-guard cells are surrounded by 2 subsidiary
cells.
Haplocheilic-guard cells surrounded by 6 or 7 subsidiary
cells.
8. Pteridospermales (seed ferns),Aiswaria Raj,St.Mary’s College
Reproductive organ
The reproductive organs were unisexual. Both the seed bearing
organs [carnoconities] & pollen bearing organs [sahnia] were born
terminally on the dwarf shoots.
Female cones looked like stalked mulberry fruits.
There were no sterile structures similar to magasporophylls.
The ovule is surrounded by single integument that was free from
nucellus.
9. Pteridospermales (seed ferns),Aiswaria Raj,St.Mary’s College
The male flowers born terminally on short lateral shoots.
Each flower consisted of a receptacle.
About 24 microsporangiophores were arranged around it in a
single whorl.
The sporangia is unilocular & contain boat-shaped pollen grains.
Each sporangium received a single vascular bundle that divided
into several radiating branches.
10. Pteridospermales (seed ferns),Aiswaria Raj,St.Mary’s College
Interrelationship
Pentoxylales resemble the cycadophytes in their leaf anatomy eg;
the diploxylic bundles & the haplocheilic stomata in leaf.
Pycnoxylic wood resemble conifers.
The pteridospermous family Medullosaceae in having a polystelic
vascular bundle.
Presence of syndeticheilic stomata, in addition to haplocheilic
[cycad character] ones is a bennettitalean character.
11. REFERENCE
Vasishta P.C, Sinha A. K., Anil Kumar, Gymnosperms, S. Chand
Publications
Pteridospermales (seed ferns),Aiswaria Raj,St.Mary’s College