Here is a list of twenty-seven fossil genera plants:- 1. Rhynia 2. Lepidodendron 3. Lepidostrobus 4. Lepidocarpon 5. Calamites 6. Calamostachys 7. Palaeostachya 8. Sphenophyllum 9. Lyginopteris 10. Kaloxtlon 11. Lagenostoma 12. Crossotheca 13. Heterangium 14. Mudullosa 15. Glossopteris 16. Vertebraria 17. Gangamopteris 18. Caytonia 19. Nipanioxylon 20. Pentoxylon 21. Sahnia 22. Carnoconite and a few others.
1. Rhynia (Fig 8.2):
Age:
Middle Devonian.
Locality:
Rhynie chart bed in Scotland.
(Mackie, 1913; Kidston and Langs, 1917).
Identifying Features:
T.S. through Rhynia (stem genus).
The following structures are seen:
(i) The stem surface is covered by cuticularised epidermis with compactly arranged cells.
(ii) Conspicuous stomata arc present.
(iii) Next to the epidermis, there is a massive cortical zone formed by compactly arranged parenchymatous cells.
(iv) There is no endodermis or pericycle.
(v) At the centre, there is a slender, hadrocentric protostele with a small central xylem core. This is surrounded by 4 – 5 layers of elongated cells with oblique ends which represent the phloem although sieve plates have not been observed.
L.S. through the sporangium of Rhynia shows the following features:
(i) The sporangia arc oval or cylindrical structures with pointed ends.
(ii) The sporangium wall is thick and multilayered with the outer cells thick-walled and inner thinner cells represent the tape-turn.
(iii) The whole interior is filled with spore tetrads or free spores.
2. Lepidodendron (Fig 8.3):
Age:
Upper Devonian to carboniferous coal fossils.
Locality:
Great Britain
Identifying Features:
L.S. of Lepidodendron (stem genus).
The following tissue zones arc noticed:
(i) The outermost surface of the stem trunk is covered by the persistent leaf bases.
(ii) There is a massive periderm zone which lies beneath the leaf bases.
(iii) Periderm layer continues internally with the cortical layer which is differentiated into three distinct zones – outer, middle and inner. Outer cortex is parenchymatous. Middle cortex is very much ruptured and formed by delicate parenchymatous cells. The inner cortex is also parenchymatous and surrounded by a secretory zone.
(iv) There are leaf traces in both middle and inner cortex.
(v) The innermost core of the stem axis is stele. It is somewhat narrower in comparison to the massive cortex. The stele is protostele with exarch and polyarch xylem, i.e., metaxylcm is at the centre with a number of protoxylem points on the periphery.
3. Lepidostrobus (Fig 8.4):
Age:
Carboniferous.
Locality:
Great Britain
Identifying Features:
L.S. through Lepidostrobus (strobilus) shows the following features:
(i) The strobilus is elliptical.
(ii) It is heterosporous and the sporophylls are arranged spirally on the strobilus axis.
(iii) The sporophylls are somewhat peltate with the upper terminal lobe clasping the sporophyll above.
(iv) The microsporangia and the mega-sporangia arc of the same size. The microsporangium encloses a large number of microspores while the mega-sporangium shows a few (about four) much larger megaspores.
4. Lepidocarpon (Fig 8.5):
Age:
Carboniferous.
Locality:
Great Britain
Identifying Features:
Median L.S. through Lepidocarpon (ovule) shows the following features:
(i) The mega-sporangium is elongated and it has an elongated beak, the tip of which is split open.
(ii) The mega-sporangium at maturity encloses a single large megaspore.
(iii) The megasporophyll tissue below the sporangium has developed a false integument which is open at the tip by a long slit forming a false micropyle.
(iv) There is a distinct vascularization at the base of the megasporophyll which is subtended by two lateral parichnos, one on each side of the vascular strand.
5. Calamites (Fig 8.6):
Age:
Upper Devonian to Lower Carboniferous.
Locality:
Europe.
Identifying Features:
T.S. through Catamites (stem) shows the following features:
(i) There is a thin periderm layer at the outermost surface of stem.
(ii) There is a distinct cortical zone just beneath the periderm. The cortex is differentiated into outer thick walled and inner thin walled zone.
(iii) At the innermost zone there is delicate pith which is broken down in mature stem to form pith cavity.
(iv) The pith is surrounded by an endarch siphonostele. The protoxylem strands have disintegrated to form carinal canals.
(v) There is massive secondary xylary tissue which lies in between cortex and primary vascular strands. It is formed by tracheids and ray cells. There is no annual ring in it.
6. Calamostachys (Fig 8.7-B):
Age:
Carboniferous.
Locality:
Europe.
Identifying features:
Median L. S. of Calamostachys (strobilus) shows the following features:
(i) The sporangiophore whorls always have whorls of sterile bracts in between.
(ii) Both kinds of whorls are arranged in a definite pattern on the axis.
(iii) Both kinds of whorls arise directly from the axis at right angles to it so that they look quite independent.
(iv) There are separate vascular supplies for both kinds of whorls and this vasculature directly arises from the vasculature of the axis.
(v) Each sporangiophore bears usually 4 peltate sporangia.
(vi) Spores are homosporous, but somewhat irregular in size.
7. Palaeostachya (Fig 8.7-A):
Age:
Carboniferous.
Locality:
Europe.
Identifying Features:
Median L.S. through Palaeostachya (stobilus) showing the following features :
(i) The sporangiophore whorls alternate with sterile bract whorls.
(ii) The sporangiophore whorls are axillary to the sterile bract whorls.
(iii) Both whorls have separate vasculature arising from a common point of the vasculature of main axis.
(iv) It is homosporous and the spores are many in the peltate sporangia which are grouped in a cluster of usually 4 on the sporangiophore axis.
8. Sphenophyllum (Fig 8.8):
Age:
Upper Devonian to lower Jurassic.
Locality:
Europe and also in Indian lower Gondwana.
Identifying Features:
T. S. through Sphenophyllm (stem) shows the following features:
(i) There is a conspicuous periderm at the outer-most surface.
(ii) Next to this layer, there is a patch of cortical zone of parenchymatous cells.
(iii) At the middle of the stem, there is a solid strand of protostele.
(iv) The primary xylem of the stele is triangular, exarch and actinostelic.
(v) There is a massive secondary xylem which is arranged in a multiseriate pattern.
9. Lyginopteris (Fig. 8.9):
Age:
Devonian to Jurassic.
Locality:
As coal ball in coal mines of England, Europe and North America.
Identifying Features:
T. S. through Lyginopteris (stem) shows the following features:
(i) There is a characteristic outer cortex with radial patches of sclerenchymatous cells.
(ii) The inner cortex is parenchymatous and often crushed in the fossil preservations due to the growth of secondary wood.
(iii) The secondary wood is composed of several rows of radially arranged multiseriate bordered-pitted tracheids.
(iv) Inside the secondary wood there are about five separate primary xylem stands which are mesarch (i.e., protoxylem is surrounded by metaxylem).
(v) There are a few leaf trace bundles lying just outside the inner cortex.
(vi) The pith is large and parenchymatous with patches of sclerenchymatous cells here and there forming sclerotic nests.
10. Kaloxylon (Fig 8.10):
Age:
Carboniferous.
Locality:
As coal ball from Lancashire, U.K.
Identifying Features:
T.S. through Kaloxylon (root) shows the following features:
(i) There is a massive cortex lying external to the stelar zone.
(ii) The cortex is differentiated into outer cortex with angular cells and inner cortex with parenchymatous cells.
(iii) There is a radial, exarch stelar cylinder with alternating phloem and xylem rays.
(iv) Sclerenchymatous bundle caps are present just outside the xylem patches.
(v) Secondary vascular tissues are present.
(vi) At the centre, there is a distinct parenchymatous pith.
11. Lagenostoma (Fig 8.11):
Age:
Carboniferous.
Locality:
As coal ball from Yorkshire, U.K.
Identifying Features:
Median L.S. of Lagenostoma (seed) shows the following features:
(i) There is a large central ovule (mega-sporangium).
(ii) The ovule is orthotropous and symmetrical.
(iii) The ovule is covered by an integument which is attached to the nucellus except at the apical pollen chamber.
(iv) The outer part of the integument is stony and inner part fleshy with vascular supply.
(v) The nucellus is free and tapering at the tip leaving a cylindrical pollen chamber.
(vi) There is a distinct cupule on which seeds are lodged. The cupule is also covered by capitate glands.
12. Crossotheca (Fig 8.12):
Age:
Carboniferous.
Locality:
England.
Identifying Features:
A fertile Crossotheca (microsporophyll bearing structure) branch shows the following features:
(i) The branch tips are slightly expanded into a circular or paddle-shaped limb.
(ii) At the tip of each branch there are a few bilocular sporangia attached together.
(iii) Each sporangium contains a number of microspores (pollens).
13. Heterangium (Fig 8.13):
Age:
Lower carboniferous.
Locality:
Scotland.
Identifying Features:
T. S. through Heterangium (stem) shows the following features:
(i) In T.S., stem is somewhat angular with de-current leaf bases.
(ii) There is a ruptured epidermal zone followed by a narrow zone containing vertical sclerenchymatous strands. This is the outer cortex zone where sclerenchymatous strands lie parallel to each other.
(iii) The inner cortex is parenchymatous with scattered sclerotic cells and leaf trace bundles.
(iv) There is a single fairly large protostele at the centre.
(v) Primary xylem is mesarch, i.e., broken up into groups by thin walled parenchyma.
(vi) There is a thin zone of secondary wood just outside the primary xylem cylinder.
14. Medullosa (Fig 8.14):
Age:
Permo Carboniferous.
Locality:
Indian Gondwana (Lower)
Identifying Features:
T. S. through Medullosa (stem) shows the following features:
(i) There is a thick parenchymatous cortex with scattered leaf trace bundles just outside the stelar zone.
(ii) There is a ring of conspicuous secondary wood zone just beneath the cortical layer.
(iii) At the central core primary vascular bundles are scattered in the parenchymatous tissues. Each bundle has distinct xylem and phloem.
15. Glossopteris (Fig 8.15):
Age:
Parmo – Carboniferous.
Locality:
Lower Gondwana (India).
Identifying Features:
The impression fossil of Glossopteris (leaf) shows the following features:
(i) Leaves are simple, entire, sessile to short petiolate, linear, lanceolate to ovate and with a very strong midrib from which numerous small fine veins pass out to the margin forming a network.
(ii) Midrib of the leaf is prominent, particularly at the base of the leaf.
16. Vertebraria (Fig B.16):
Age:
Permo – Carboniferous.
Locality:
Lower Gondwana (India).
Identifying Features:
The petrified fossil of Vertebraria (stem) shows the following features:
(i) The stem axis is flattened and grooved.
(ii) The axis shows 2-3 series of rectangular blocks of alternate ridges and furrows.
17. Gangamopteris (Fig 8.17):
Age:
Permo – Carboniferous.
Locality:
Lower Gondwana (India).
Identifying Features:
The impression fossil of Gangamopteris (leaf), showing the following features:
(i) The leaves are simple and ovate to lanceolate in shape.
(ii) There is absence of distinct midrib.
(iii) Lateral veins show parallel anastomosing features and thus forming a reticulate network.
18. Caytonia (Fig 8.18):
Age:
Jurassic to Cretaceous.
Locality:
England.
Identifying Features:
Vertical sectional view of Caytonia (megasporophyll) shows the following features:
(i) It is a flat structure bearing a cupule around the ovule.
(ii) Each ovule has a rounded body with an opening, close to the pedicel.
(iii) A row of 7 to 8 small orthotropous seeds are situated in a row on the curved inner face.
(iv) There is a single integument completely free from the nucellus.
19. Nipanioxylon (Fig 8.19B):
Age:
Lower Jurassic.
Locality:
Upper Gondwana (India).
Identifying Features:
The impression fossil of NipanioxyIon (leaf) shows the following features:
(i) The leaf is strap shaped with a distinct midrib which is formed by several strong parallel veins.
(ii) Each parallel vein is branched and runs parallel to the margin. These branch veins may show forking at the ends.
20. Pentoxylon (Fig 8.19A):
Age:
Lower Jurassic.
Locality:
Upper Gondwana (India).
Identifying Features:
T. S. through Pentoxylon (stem) shows the following features:
(i) There are two rings of steles – inner ring is formed of 5 – 6 larger steles in each of which there is conspicuous endocentric secondary wood, i.e., a greater part of the wood is formed towards the pith.
(ii) Alternating with these inner rings of larger steles there is one outer ring of smaller steles. These steles are formed of secondary wood.
(iii) There are distinct growth rings in each larger stele.
21. Sahnia (Fig 8.19C):
Age:
Lower Jurassic.
Locality:
Upper Gondwana (India).
Identifying Features:
Vertical section through Sahnia (male flower) shows the following features:
(i) Micro-sporophylls are branched and fused at the base to form a tubular disc.
(ii) The final branches bear unilocular Microsporangia at the tips.
22. Carnoconites (Fig 8.19D):
Age:
Lower Jurassic.
Locality:
Upper Gondwana (India).
Identifying Features:
L. S. through Carnoconites (female cone) showing the following features:
(i) The cone is pedunculate and each branch bears a female cone.
(ii) Each cone has an axis bearing spirally arranged sessile ovules directly on it.
(iii) There is no scale, bract or megasporophyll which is associated with it.
(iv) The seed shows thick, fleshy integument and protruding micropyle.
23. Cordaites (Fig 8.20):
Age:
Upper Carboniferous.
Locality:
Lower Gondwana (India),
Identifying Features:
T. S. through Cordaites (stem) shows the following features:
(i) There is a distinct periderm which forms the outermost covering of the stem.
(ii) There is a massive cortex which is parenchymatous with gum canals.
(iii) There are a few leaf trace bundles in the innermost layer of cortex.
(iv) There is a large parenchymatous pith found at the centre of the stem.
(v) In between pith and cortex, there is secondary wood which often cracked transversely giving the appearance of a pile of concave discs.
24. Amyelon (Fig 8.21):
Age:
Upper Carboniferous.
Locality:
Lower Gondwana (India).
Identifying Features:
T. S. through Amyelon (root) shows the following features:
(i) There is a uniformly thick periderm as outer covering of the axis.
(ii) There is also a parenchymatous cortex just below the periderm layer.
(iii) There is a central triangular protostele which is often triarch (rarely diarch or tetrarch).
(iv) In between primary xylem and cortex, there is a very thick secondary wood zone.
(v) Pith is absent.
25. Cordaites (Fig 8.22):
Age:
Upper Carboniferous.
Locality:
Lower Gondwana (India).
Identifying Features:
T. S. through Cordaites (leaf) shows the following features:
(i) There are two distinct cutinised, thick walled epidermal layers.
(ii) There is also a thick walled hypodermis just beneath the epidermis which extends up to the bundle sheath.
(iii) Stomata are present in the lower epidermis.
(iv) Mesophyll cells are distinct and lie in between two epidermal and hypodermal zones.
(v) There are conjoint, collateral, closed vascular bundles surrounded by bundle sheath of 1 – 2 layers of thick cells.
(vi) Transfusion tissue is present in between two bundles.
26. Cordaianthus (Fig 8.23):
Age:
Upper Carboniferous.
Locality:
Lower Gondwana (India).
Identifying Features:
Median L.S. of Cordaianthus (strobilus) shows the following features:
(i) A male strobilus contains a few microsporophyll’s or stamens each supporting terminal sporangia.
(ii) The female strobilus contains a few megasporophylls or carpels each bearing a terminal mega sporangium or ovule.
(iii) The ovule or mega sporangium shows an elongated oval nucellar mass completely free from the single integument which is extended into a short micropylar canal at the top.
27. Mitrospermum (Fig 8.24):
Age:
Upper Carboniferous.
Locality:
Lower Gondwana (India).
Identifying Features:
L. S. through Mitrospermum (seed) shows the following features:
(i) The seed is flattened and heart shaped.
(ii) The nucellar portion is surrounded by an integument whose outer layer is expanded into a wing-like outer testa and the inner layer forms a hard, sclerotic testa.
(iii) There is a vein derived from the pedicel which divides into two and then supplies the integument.