General characters of pteridophytes

General characters of pteridophytes

• 1.
  General Characters of Pteridophytes
• 2.
  Introduction • Pteridophtes arevascular 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 ofPteridophyta • 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 areflowerless 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 gametophyticplant 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 majorityof 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 beendivided into following classes: • Psilopsida • Lycopsida • Sphenopsida • Pteropsida
• 8.
  PSILOPSIDA • Vascular tissueis 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 mossesand 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 includesplants 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 includesplants with fan-shaped leaves • Plant body highly developed, stem usually rhizome • In some ferns stem is erect and may go up to 15ft • 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 steleis 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 isthe 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 stelexylem 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
• 16.
   Siphonostele • Inthe 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
• 18.
  • Siphonostele classifiedon 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
• 19.
  Dictyostele In many Filicophytaleaves 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
• 20.
  Other type ofstele • 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