Plant Kingdome - Pteridophytes | NCERT concept | Neet Concept | Biology

Plant Kingdome - Pteridophytes | NCERT concept | Neet short material| Biology

PTERIDOPHYTES

• Pteridophytes are seedless vascular plants that have sporophytic plant body and inconspicuous gametophytes .
• The sporophyte is differentiated into true roots , stem and leaves .
• All the vegetative parts possess vascular tissues ( xylem and phloem ) organised in definite groups or steles.
• On the basis of leaf structure , pteridophytes may be microphyllous ( having simple leaves with single vein , which do not form leaf gaps in the stem stele ) , e.g. , Equisetum and megaphyllous ( having pinnate leaves with complex sereis of veins that form prominent leaf gaps in the stem stele ) , e.g. , Pteris .
• The branching of the stem may be dichotomous type or monopodial .
• The sporophyte reproduces asexually by means of spores , produced in small capsules called sporangia . PTERIDOPHYTES  
• Leaves bearing sporangia are called sporophylls which may be widely scattered or clustered in definite areas and structures called cones or strobili .
• The diploid spore mother cells or sporocytes within the sporangia undergo meiosis to form haploid spores .
• The spores produced are of only one type in homosporous pteridophytes ( e.g. , Lycopodium , Pteridium ) or of two types ( smaller microspores and larger megaspore ) in heterosporous pteridophytes ( e.g. , Selaginella , Marsilea ) .
• The spores germinate to produce haploid gametophyte , called prothallus .
• The homosporous pteridophytes produce bisexual gametophytes ( both antheridia and archegonía are borne on same prothallus ) whereas heterosporous ones produce unisexual ( antheridia and archegonia develop on separate male and female prothallus ) gametophytes .
• The sexual reproduction is oogamous type .
• Antheridia are small and sessile male sex organs comprising of androcytes each of which produces a male antherozoid . Archegonia are female sex organs partially embedded and consists of 4 - rowed neck .
• Water is essential for fertilisation , as it assists in carrying bi - or multiflagellate sperms to archegonia .
• The diploid zygote formed after fertilisation develops into an embryo which remains attached to the gametophyte and gets nourishment during its early stage of development .
• Pteridophytes exhibit alternate succession of sporophytic and gametophytic generation.

Pteridophytes can be classified into following types :

• Psilopsida
• These are oldest known land inhabiting plants . Rootless , rhizoids are present . Homosporous Most plants are fossils , e.g. , Rhynia , Horneophyton etc.

• Lycopsida
• Commonly called club mosses or spike mosses . Roots , stem and leaves are present . Members are microphyllous . Homosporous ( Lycopodium ) or heterosporous ( Selaginella ) .
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• Sphenopsida
• At nodes , whorls of small leaves are present . Deposition of silica in stems make them rough in touch . Ridges and grooves are found in stem . Always homosporous , e.g. , Equisetum .

• Pteropsida / Filicopsida
• Fan like leaves . Stem is in the form of rhizome . May be homosporous ( Dryopteris , Pteris ) or heterosporous ( Marsilea ) .

Importance of Pteridophytes

• Food : Pteridophytes constitute a good source of food to animals . Sporocarps of Marsilea are cooked and eaten by certain tribals
• Binding of soil : Pteridophytes bind the soil even along hill slopes , thus , preventing soil erosion .
• Scouring : Stems of some plants are used in scouring or cleaning of utensils and polishing of metals , e.g. , Equisetum .
• Nitrogen fixation : Some ferns e.g. , water fern Azolla form symbiotic association with nitrogen fixing cyanobacterium Anabaena azollae . These are used as biofertilisers in paddy fields .
• Medicines : Rhizomes of male shield fern are used to obtain anti - helminthic drug . Equisetum is used in preparation of diuretic , haemostatic and haemopoietic drugs .
• Ornamentals : Ferns are known for their attractive foliage , hence are grown as ornamental plants and used in bouquets .

• Evolution of Seed Habit
• The ability of plant to form seed is called seed habit . It is considered to be originated in pteridosperms during Devonian carboniferous periods . The development of zygote into young embryo within female gametophyte in heterosporous plants ( e.g. , Selaginella ) is a precursor to the evolution of seed habit .  and floral decorations .
• The differentiation of spores into microspores and megaspores ( heterospory ) and their dependence on the parent sporophyte for the nutrition are certain features considered as pre - requisites for the formation of seeds .

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