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Lepidodendron.pptx palaeobotany slide....

The document discusses the taxonomic position, features, and reproductive structures of Lepidodendron, a tree-like lycopod from the Carboniferous period. It details its classification, morphology, cone structure, and unique reproductive traits, including its potential transition towards seed-like characteristics. Lepidodendron is notable for its size, habitat in prehistoric coal swamps, and its contribution to the understanding of plant evolution.

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Dr. R. D. Anpin Raja Lepidodendron Taxonomic position, Features & Reproductive Structure 3D illustration of the triceratops in Lepidodendron grove
TAXONOMIC POSITION Division : Pteridophyta Class :Lycopsida Order :Lepidodendrales Family :Lepidodendraceae Genus :Lepidodendron Lepidodendron: Taxonomic position, Features & Reproductive Structure
Lepidodendron Reconstructed from 4 fossil form genus 1. Stigmaria 2. Lepidophylloides 3. Lepidostrobus 4. Lepidocarpon Lepidodendron: Taxonomic position, Features & Reproductive Structure
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
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
 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
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
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
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 dichoto­ mous 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
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
ANATOMY: STEM Lepidodendron: Taxonomic position, Features & Reproductive Structure Cortex had 4 regions 1. Inner cortex: Homogenous, parenchymatous without leaf trace 2. Secretory zone: Intermingled large and small cells, filled with dark coloured substance 3. Middle cortex: delicate cells which were often destroyed 4. Outer cortex: alternate radial masses of thick and thin walled elements
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
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 mega­ sporangia formed at the basal portion of the cones  Both the sporophylls were identical, except for their spore content.
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
STROBILUS: SPORES Lepidodendron: Taxonomic position, Features & Reproductive Structure  The microspores were small with smooth or granular exine.  Megaspores were spherical, slightly elon­ gated, 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
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
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
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
LEPIDOCARPON: SEED HABIT Lepidodendron: Taxonomic position, Features & Reproductive Structure Shows simi­ larity with an ovule of gymnosperm 1. Formation of a single functional megaspore in the megasporangium 2. Retention of functional megaspore in the megasporangium 3. Formation of endosporic megagameto- phyte within megasporangium 4. Formation of an integument that delimited a microphyle
LEPIDOCARPON: FALSE SEED Lepidodendron: Taxonomic position, Features & Reproductive Structure  not reached the level of a seed (ovule),  basic charac­ teristics 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)
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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