Lepidodendron.pptx palaeobotany slide....

fossil plant study

1. Dr. R. D. Anpin Raja Lepidodendron Taxonomic position, Features & Reproductive Structure 3D illustration of the triceratops in Lepidodendron grove

2. TAXONOMIC POSITION Division : Pteridophyta Class : Lycopsida Order : Lepidodendrales Family : Lepidodendraceae Genus : Lepidodendron Lepidodendron : Taxonomic position, Features & Reproductive Structure

3. Lepidodendron Reconstructed from 4 fossil form genus Stigmaria Lepidophylloides Lepidostrobus Lepidocarpon Lepidodendron : Taxonomic position, Features & Reproductive Structure

4. Lepidodendron also known as “scale tree” one of the most abundant trees of the Carboniferous period It lived in some of the wettest parts of the prehistoric coal swamps commonly grew in dense stands only lived about 10 to 15 years. Lepidodendron : Taxonomic position, Features & Reproductive Structure

5. Lepidodendron Groups of arborescent (tree like) lycopods evolved from the Middle Devonian lycopods The petrified trunks were sometimes as long as 100 feet assumed that the plant reached a height of over 160 ft (50 m) trunks were often over 1 m diameter Lepidodendron with 100 species the best-investigated genus Fossils from Sandstones of coal bearing formations Lepidodendron : Taxonomic position, Features & Reproductive Structure

6. Trunk was straight up to 35 m height). Dichotomously branched only at the top Branches were short Ultimate dichotomies produced the leaves. The branches and the foliage formed as a crown at the apex of the long trunk Cones formed at their tips. Lepidodendron : Morphology Lepidodendron : Taxonomic position, Features & Reproductive Structure

7. MORPHOLOGY: LEAF Lepidodendron : Taxonomic position, Features & Reproductive Structure Branches were covered spirally arranged leaves very rarely they showed a whorled arrangement. They are placed in the form genus - Lepidophylloides Simple, ligulate acicular to linear in shape having a length of 5-9 inches Each leaf had a single vein stomata situated in two bands on the ventral surface

8. MORPHOLOGY: LEAF The leaves were deciduous Leaves were attached to a pyramidal cushion like leaf base After abscission a flat rhomboidal scar persisted on the stem resembling a small cushion These scars formed as oblique or spiral rows on the stem Actual leaf scar was formed above the middle line of rhombus 3 types leaf scars were formed; Ligule scar, bundle scar and parichnos scar (Loosely arranged parenchyma) Lepidodendron : Taxonomic position, Features & Reproductive Structure Lepidodendron on display at the State Museum of Pennsylvania

9. MORPHOLOGY: ROOT Lepidodendron : Taxonomic position, Features & Reproductive Structure The base of the stem was attached to the root system Root system is included in the form genus, Stigmaria In S. ficoides , base of the trunk is divided into 4 massive rhizophore Rhizophore later again form repeated dichoto­mous branches in the horizontal plane The Stigmaria spread over an area of about 20 ft (6 m) across younger portions had spirally arranged roots , known as Stigmarian rootlet

10. ANATOMY: STEM Lepidodendron : Taxonomic position, Features & Reproductive Structure Outer most part was a periderm formed by phellogen Shows a protostele or siphonostele with exarch and polyarch xylem Metaxylem present at the center and protoxylem pointing towards the periphery A ring of cambium situated outside produced a narrow zone of secondary xylem Both primary and secondary xylem were made of scalariform and spiral tracheids

11. ANATOMY: STEM Lepidodendron : Taxonomic position, Features & Reproductive Structure Cortex had 4 regions Inner cortex: Homogenous, parenchymatous without leaf trace Secretory zone: Intermingled large and small cells, filled with dark coloured substance Middle cortex: delicate cells which were often destroyed Outer cortex: alternate radial masses of thick and thin walled elements

12. STROBILUS Lepidodendron : Taxonomic position, Features & Reproductive Structure Cones or strobilus that were borne terminally on the small branches also called Flemingites Fossils discovered from the Paleozoic era are placed in the form genus (organ genus), Lepidostrobus All known species are Heterosporous Elliptical, 1-7.5 cm in diameter and 2.5 to 30 cm or more long The sporophylls were helically attached to the central cone axis

13. STROBILUS Lepidodendron : Taxonomic position, Features & Reproductive Structure Each sporophyll bore a single sessile sporangium on its adaxial face Just beyond sporangium, a ligule was present microsporophylls bearing microsporangia were usually borne in the apical portion megasporophylls bearing mega­sporangia formed at the basal portion of the cones Both the sporophylls were identical, except for their spore content.

14. STROBILUS: SPORANGIUM Lepidodendron : Taxonomic position, Features & Reproductive Structure Large sac like structures wider than sporophyll Wall was made up of a single layer of cells Some radiating flaps of tissue called trabeculae extended upward from the base of sporangium Micro and megasporangia - same size micro sporangium enclosed several hundred microspores Megasporangium enclsed 4,8, or 16 megaspores Megaspore showed gametophytic development within the megasporangium

15. STROBILUS: SPORES Lepidodendron : Taxonomic position, Features & Reproductive Structure The microspores were small with smooth or granular exine . Megaspores were spherical, slightly elon­gated , showing trilete aperture with echinate (spinous) exine Megaspore tetrads were attached tetrahedrally The megaspore germinated endosporically to form multicellular prothallus Prothallus formed rhizoids and interdispersed archegonia comprised of one to three tiers of neck cells. Lepidostrobus variabilis . Carboniferous Period: Coal measures, about 300 million years old. Shrewsbury Museums Service

16. Lepidodendron : Taxonomic position, Features & Reproductive Structure The female gametophyte is included in the form genus , Lepidocarpon known only from its strobilus The fossils were obtained from the coal strata in England and U.S.A. The strobili named Lepidostrobus strobili is monosporangiate though the plant was heterosporous. The megasporophylls bore elongate megasporangia on their adaxial surface. Lepidodendron aculeatum in siderite Mazon Creek LEPIDOCARPON : Female gametophyte

17. Lepidodendron : Taxonomic position, Features & Reproductive Structure The jacket of the mega-sporangium extended at the apex to form a projection. The sporangium was enveloped by the flaps of a tissue which is termed as integument But in reality, this is an upturning of the megasporophyll many workers believe it to be a special outgrowth from the megasporophyll . There were four spores in a sporangium only one developed into the female gametophyte. LEPIDOCARPON : Female gametophyte

18. Lepidodendron : Taxonomic position, Features & Reproductive Structure The mega-sporangial cavity also showed many spores some of them - microspores of Lepidocarpon Indicate the posibilty of incipient pollination also seen in the extant genus Selaginella . unique feature - permanent retention of the mega-gametophyte within the sporangium not seen in any lycopods extinct or extant significant step to evolution of seed habit megasporophylls liberated and on falling upon a suitable substratum embryo developed into the sporophyte LEPIDOCARPON : Female gametophyte

19. LEPIDOCARPON : SEED HABIT Lepidodendron : Taxonomic position, Features & Reproductive Structure Shows simi­larity with an ovule of gymnosperm Formation of a single functional megaspore in the megasporangium Retention of functional megaspore in the megasporangium Formation of endosporic megagameto-phyte within megasporangium Formation of an integument that delimited a microphyle

20. LEPIDOCARPON : FALSE SEED Lepidodendron : Taxonomic position, Features & Reproductive Structure not reached the level of a seed (ovule), basic charac­teristics of a seed - totally absent megasporangium wall is dehiscent, indehiscent in an ovule (seed). In Lepidocarpon , fertilisation took place with the help of water , where archegonia were exposed and flagellated sperms had direct access to the ovum of archegonia. However, siphonogamous fertilisation through pollen tube is the characteristic feature of spermatophytes. The integument of Lepidocarpon is foliar in nature (the presence of parichnos )

21. LEPIDOCARPON : FALSE SEED Lepidodendron : Taxonomic position, Features & Reproductive Structure The seed-like features is not an unusual phenomenon. permanent retention - also been reported in some members of Selaginellales and Isoetales . The so-called integument -described as water or moisture retaining structure or as protective adaptation. So, Lepidocarpon should at best be regarded as a FALSE SEED or pseudo- spermatophyte.

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