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Stelar evolution in Pteridophytes

The document discusses the evolution of steles, or vascular bundles, in pteridophytes. It describes the basic types as protostelic and siphonostelic. Protostelic steles have central xylem and surrounding phloem with no pith, while siphonostelic steles have a central pith. Specific protostelic types include haplostele, actinostele, and plectostele. Siphonostelic types include cladosiphonic, phyllosiphonic, ectophloic, amphiphloic, solenostele, dictyostele, and polycyclic steles. The origin of

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STELAR EVOLUTION IN PTERIDOPHYTES DR. JAYAKARA NHANDARY M. ASSOCIATE PROFESSOR & HEAD DEPT. OF BOTANY GAS COLLEGE, KARWAR
BASIC TYPES OF STELES • PROTOSTELE – Central Xylem, surrounding Phloem. No Pith. Primitive • SIPHONOSTELE – Protostele with Central Pith. Advanced
TYPES OF PROTOSTELES • Haplostele – Central circular Xylem. Rhynia • Actinostele – Star shaped Xylem. Ex. Psilotum, Lycopodium serratum • Plectostele- Xylem broken into many parallel plates. Ex. L. clavatum • Mixed Protostele – Small irregular patches of Xylem. Ex. L. cernuum
TYPES OF SIPHONOSTELES • Cladosiphonic – No leaf traces • Phyllosiphonic – with leaf traces • Ectophloic – Phloem outside xylem . Ex. Equisetum • Amphiphloic – Outer and inner rings of Phloem, Xylem central. Ex. Marselia
TYPES OF SIPHONOSTELE • Solenostele – Non-overlapping leaf traces. Ex. Adiantum • Dictyostele- Overlapping leaf traces Ex. Ophioglossum • Polycyclic – Two or more concentric rings of vascular tissue. Complex type. Ex. Pteris
Origin of Siphonostele • Intra stelar Origin – Pith developed from inner xylem cells. • Extra stelar Origin – Pith formed by outer cortical cells which entered inside through leaf gaps.
Evolution of Stele