2 Classification of Pteridophytes.pptxuuu

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1. Reimer (1954) proposed a classification for Pteridophytes. In this classification, the Pteridophytes are divided into five subdivisions. 1. Psilophytopsida 2. Psilotopsida 3.. Lycopsida 4.  Sphenopsida 5.         Pteropsida. There are 19 orders and 48 families in the classification

2. Subdivision Order Family Genus Psilophytopsida Psilophytales Rhyniaceae Rhynia Psilotopsida Psilotales Psilotaceae Psilotum Lycopsida Protolepidodendrales Protolepidodendraceae Protolepidodendron Lycopodiales Lycopodiaceae Lycopodium Lepidodendrales Lepidodendraceae Lepidodendron Isoetales Isoetaceae Isoetus Selaginellales Selaginellaceae Selaginella Sphenopsida Hyeniales Hyeniaceae Hyenia   Sphenophyllales Sphenophyllaceae Sphenophyllum Calamitales Calamitaceae Calamites Equisetales Equisetaceae Equisetum Pteropsida       Sub-Class: Primofilices Cladoxylales Cladoxylaceae Cladoxylon Coenopteridales Stauropteridaceae Stauropteris Sub-Class: Eusporangiatae Marattiales Angiopteridaceae Angiopteris Ophioglossales Ophioglossaceae Ophioglossum Sub-Class: Osmundidae Osmundales Osmundaceae Osmunda Sub-Class: Lepidosporangiate Filicales Cyatheaceae Cyathea Marsileales Marsileaceae Marsilea Salviniales Salviniaceae Salvinia

3. Stelar Evolution in Pteridophytes The term ‘stele’ was first proposed by Van Tieghem and Douliot (1886) Stele of a plant includes Pericycle Phloem Xylem Medullary rays Cambium

4. There are three major types of Stele Protostele – stele without pith Siphonostele – stele with pith but no leaf gap Solenostele – stele with pith and leaf gap

5. Protostele Stele with solid core of xylem at the centre and it is surrounded by phloem Pith is absent Considered as the most primitive in origin Majority of the Pteridophytes show protostelic condition in their rhizome, stem, or roots

6. There are five types of protostele Haplostele Actinostele Plectostele Mixed protostele Mixed protostele with pith

7. Haplostele Protostele with a smooth core of xylem surrounded by uniform layers of phloem Named by Brebner in 1902. Most primitive type of stele found in Rhynia, Lygodium

8. Actinostele Protostele with xylem core having radial ribs or arms Xylem is star shaped Phloem do not have continuous distribution but as separate patches Named by Brebner in 1902 Ex. Psilotum, Lycopodium

9. Plectostele Xylem occurs as several plates which are more or less parallel to each other Xylem plates are alternate with phloem patches Named by Zimmermannn in 1930 Eg. Lycopodium clavatum

10. Mixed protostele Xylem is divided into several units or groups Each Xylem units are scattered inside the mass of phloem Eg. Lycopodium cernuum

11. Siphonostele A stele with pith (medulla) at the centre The pith is surrounded by xylem Advanced type than the protostele There are two types of siphonostele based on the position and distribution of phloem Ectophloic siphonostele Amphiphloic siphonostele

12. Origin of siphonostele There are two views for the origin of siphonostele Inter – stelar origin of pith which is widely accepted theory of pith development Proposed by Bower in 1923 and supported by Fahn in 1960 Innermost vascular tissue in a protostele changes into parenchymatours pith Extra-stelar origin of pith Proposed by Jeffery Pith and cortex are homogenous structures Pith is formed by the invasion of cortical parenchmatous cells into the stele Invasion of pith occurs through the leaf gap or branch gap

13. Ectophloic siphonostele Phloem present only on the external side of the xylem Pith is at the central position Phloem is externally surrounded by pericycle and endodermis Leaf traces present but leaf gap is absent Eg. Osmunda

14. Amphiphloic siphonostele Phloem is present on both sides of the xylem Central portion of the stele is occupied by pith Xylem on inner side is surrounded by inner phloem, pericycle and endodermis Xylem on outer side is surrounded by outer phloem, pericycle and endodermis Eg. Marselia, Adiantum

15. Solenostele Solenostele is actually a sub category of siphonostele Perforation of leaf trace is the distinguishing feature of solenostele In simple, asiphonostele with leaf gap is called solenostele There are five types of solenostele Ectophloic solenostele Amphiphloic solenostele Dictyostele Eustele – found in angiosperms Atactostele – found in angiosperms

16. Ectophloic solenostele Derived from ectophloic siphonostele Thus phloem is present only on the outer side of the xylem

17. Amphiphloic solenostele Derived from amphiphloic siphonostele Phloem is present on both sides of the xylem Phloem in both sides is intern surrounded by pericycle and endodermis Eg. Adiantum pedatum

18. Dictyostele Solenostele that is broken into a network of separate vascular strands This is due to the presence of large number of leaf gaps Each such separate vascular strand is called meristele Eg. Pteris