General characters of pteridophytes

General characteristics are discussed in this ppt

1. General Characters of Pteridophytes

2. Introduction Pteridophtes are vascular cryptogams i.e. plants of this group produce vascular tissues i.e. xylem and phloem for conduction of water, minerals and for translocation of food Evolutionarily they are the first terrestrial plants to possesses vascular tissues They are mostly herbaceous and found in cool and shady places, though some may flourish in sandy soil condition Equisetum

3. General Characteristics of Pteridophyta The main plant body is sporophyte which is differentiated into true roots, stem and leaves e.g. selaginella Leaves are small called microphylls as in selaginella or large called macrophylls as in true ferns Vascular tissue is differentiated into xylem and phloem

4. These are flowerless plants Sporophytes bearing sporangia that are subtended by leaf like appendages called sporophylls The sporangia produce spores by meiosis in spore mother cell The spores germinate to produce multicellular free living, photosynthetic thalloid gametophyte called prothallus They need water for fertilization and the spread of pteridophytes is limited and restricted to narrow geographical region General Characteristics of Pteridophyta

5. The gametophytic plant is smaller and less differentiated The gametophyte bears male reproductive structures called antheridia and female reproductive structures called archegonia The antheridia bear antherozoids and archegonia bear oosphere The plants show definite alternation of generation Zygote produces a multicellular well differentiated sporophyte which is the dominant phase of the pteridophytes General Characteristics of Pteridophyta

6. In majority of pteridophytes all the spores are of similar kinds, such plants are called homosporous Some pteridophytes produce two types of spores mega and micro and are called heterosporous Megaspores and microspores germinate and give rise to female and male gametophytes respectively e.g. Selaginella and Salvinia General Characteristics of Pteridophyta

7. Pteridophytes has been divided into following classes: Psilopsida Lycopsida Sphenopsida Pteropsida

8. PSILOPSIDA Vascular tissue is present only in stem Rhizoids are present for absorption of water and minerals Leaves usually absent Sporangia terminal and homosporous Many plants are extinct, only four species are living e.g. Psilotum

9. Club mosses and spike mosses Plants divided into stem, leaves and roots Vascular tissue is found in all organs of the plants Leaves are small and thin Most plants bear a group of sporophylls at the apices of branches which is called cone or strobilus Some plants are homosporous like Lycopodium others are heterosporous like Selaginella LYCOPSIDA

10. This includes plants with very small leaves which are arranged in whorls on nodes There are ridges and grooves on the stem Always homosporous e.g. Equisetum SPHENOPSIDA Equisetum

11. This includes plants with fan-shaped leaves Plant body highly developed, stem usually rhizome In some ferns stem is erect and may go up to 15 ft Sporangia are born on lower surface, either in the middle or on the margins of sporophylls They may be homosporous e.g. Dryopteris , Pteris , Adiantum or heterosporous e.g. Marsilea Spores germinate to produce gametophytes bearing antheridia and archegonia PTEROPSIDA

12. The stele is the fundamental unit of vascular system i.e. present in root or stem The stele consists of the vascular tissues, pericycle and the pith The innermost layer of cortex is endodermis and pericycle is the outermost layer of the stele In pteridophytes following kinds of stele is recognized: Protostele Siphonostele Stelar System in Pteridophytes

13. Protostele It is the simplest and most primitive type of stele in which the vascular tissues form a central solid mass of xylem surrounded by phloem. Pith is absent Protosteles are of following types: Haplostele It is the small core of xylem surrounded by a uniform layer of phloem e.g. Rhynia which is fossil plant and Selaginella kraussiana Actinostele It has a xylem core with radiating arms. In actinostele phloem is present in the form of separate patches alternating with radiating arms of xylem e.g. Lycopodium serratum

14. Plectostele In this stele xylem occurs in the form of small parallel bands alternating with phloem plates e.g. Lycopodium clavatum Mixed protostele with phloem In this stele xylem groups are scattered in the form of irregular patches that are embedded in the ground mass of phloem e.g. Lycopodium cernuum Mixed protostele with parenchyma In this stele xylem groups are scattered in the form of irregular patches that are embedded in the ground mass of parenchyma e.g. Hymenophyllum demissum

15. Siphonostele In the siphonostele the centrally placed xylem core is replaced by parenchymatous cells and therefore central parenchymatous pith surrounded by xylem is present in the siphonostele. It is of two types Ectophloic siphonostele In this stele xylem is in the form of hollow cylinder surrounding a pith with the phloem occurring only outside the xylem e.g. Schizaea , Osmunda Amphiphloic siphonostele the xylem form a hollow cylinder enclosing the pith with the xylem occurring both on the inner and outer side of the xylem e.g. Adiantum , Marsilea

16. Siphonostele classified on the basis of leaf gaps. They are of two kinds: Solenostele Siphonostele which are perforated by scattered leaf gaps are known as solenostele. They are of two types: Ectophloic solenostele Amphiphloic solenostele

17. Dictyostele In many Filicophyta leaves are inserted on the stem in close succession. In such cases leaf gaps overlap thus the vascular cylinder of stem appears dissected into meristeles separated from one another by parenchymatous tissue or leaf gaps These meristeles appear arranged in a ring. Such a stele is known as dissected siphonostele or dictyostele. e.g. Dryopteris fillix-max

18. Other type of stele Polycycle stele The vascular tissue is present in the form of two or more concentric cylinders e.g. Pteridium aquilinum. Polycyclic steles may be polycyclic solenosteles or polycyclic dictyosteles. Polystele Sometimes more than one steles are present in the axis of some Pteridophytes e.g. Selaginella kraussiana , S.laevigata