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Home , Megaspore, Pteridophyte

Pteridophyta – Vascular

Dr. Pallavi J.N.L College Khagaul

Division of Pteridophyta includes four classes. • Psilopsida: • Lycopsida: Lycopodium, • Sphenopsida: (Horse tail) • Pteropsida or Filicopsida: Pteridium, Adiantum

GENERAL CHARACTERISTICS • Pteridophytes (pteron= feather, phyton= , i.e. with feather like ). • These are also known as vascular cryptogams. • They are represented by about 400 living and genera and some 10,500 species. • These plants originated about 380 million years ago in the Silurian period of the Paleozoic era and formed dominant vegetation on the earth during the period. HABITAT • Most of the living pteridophytes are terrestrial, growing in moist and shady places. • Some members are aquatic (, Marsilea, Salvinia) usually occurring in permanent ponds. • A few forms are xerophytic like Equisetum. • the greatest diversity of pteridophytes is found in the tropics, with only about six hundred species adapted for in temperate climates. Species living today are relics of ancient lineages that once dominated • reproduce by releasing rather than . • There is a rich record showing that pteridophytes have ancestors dating back nearly four hundred million years. Before there were plants, there were pteridophytes such as large, treelike (up to 36.5 meters [120 feet] tall) Lepidodendron, an ancestor of modern club (which are no more than .30 meter [1 foot] tall), and shrubby PLANT BODY • They show much variation in their form, size and . They ranges from small annual (e.g. Azolla) to large -like perennials. • The main plant body is sporophytic, differentiated into , stem and leaves. • The primary are ephemeral and are soon replaced by adventitious roots (which develop on ).

• The stem is an underground rhizome by which ferns reproduce vegetatively. Some primitive ferns have tree-like stem. • The leaves are scaly (Equisetum), small and sessile (e.g Lycopodium), or large, petiolate and compound (Ferns).

• Leaves may be small microphyllous (Lycopodium) or large megaphyllous (Pteris). These are called fronds. • The root and stem have well developed vascular system, composed of and . The xylem is made up of tracheid and the phloem has sieve tubes only. Cambium is absent. • Internal structure • The vascular system in both rhizome and aerial stems is a protostele. It is a solid vascular cylinder consisting of a fluted cylinder of xylem (actinostele) completely surrounded by phloem. As in the dicot root vascular cylinder (solid, ridged xylem cylinder with radial xylem/phloem arrangement), Psilotum has a similar format. REPRODUCTION

• Vegetative reproduction takes place by fragmentation of rhizome, adventitious etc. • They reproduce by spores, produced in sporangia. The sporsporangia are usually borne on the ventral surface of the . • Sporangia occur on the surface of leaves in cluster called sori. (Sing. Sorus) and these leaves, bearing sporangia, are known as • The sporophylls with megasporangia are called megasporophylls and with are called microsporophylls. • Sporophylls are either unifromly distributed or are aggregated into compact cones (known as strobili) at the apex of the stem. • In aquatic forms like Azolla, Salvinia, and Marsilea the sporangia are present within specialized structure called sporocarps. • Most pteridophytes are homosporous, i.e. they produce only one type of spores, e.g., Lycopodium, Equisetum etc. • Some others are heterosporous, i.e. they produce two types of spores (microspres and ). The megaspore and germinate to give rise female and male respectively. • Gametophyte is a thalloid, called . It is a free-living gametophyte bearing sex organs, antheridia and archegonia. • The antheridia are small hemispherical structures enclosing 32-48 sporocytes ( mother cell). • The antherozoids are unicellular, uninucleate and spirally coiled flagella. • The is flask-shaped structures that are partially embedded in the prothallus. Neck of archegonium has 4 vertical rows of cells. • Water is essential for fertilization. The antherozoid and egg fuse to form a diploid zygote, which functions as the mother cells of generation. • Fertilization and and development of zygote into young take place within the young gametophyte. This event is a precursor to the seed habit considered as an important step in evolution. • The life cycle shows alternation of generation in which a dominant sporophyte and an inconspicuous gametophyte

• ECONOMIC IMPORTANCE • Ornamental value : Because of their delicate and graceful foliage, ferns are grown as ornamental plants in gardens. • Drugs : Rhizome and of Dryopteris yield an antihelminthic drug. Lycopodium is used in the treatment of rheumatism and Adiantum roots help to cure throat infection. • Food : Some are rich source of . • Soil binding : Pteridophytes protect the soil from erosion even along hill slopes by binding the soil. • Scouring : Equisetum stems are used in scouring (cleaning of utensils) and polishing of metals. • Biofertilisers : Azolla has a symbiotic association with nitrogen-fixing cyanobacterium, Anabaena. It is inoculated to paddy fields to function as a biofertilisers. • Similarities with : • (i) Plant body is sporophytic, dominant and can be differentiated into root, stem and leaves in both the groups. • (ii) Gametophytic phase is of short duration. • (iii) Young leaves show circinate vernation. • (iv) Vascular is well developed. Xylem lacks vessels (except in Gnetales of Gymnosperms) and companion cells are absent in phloem). • (v) Like Gymnosperms many Pteridophytes are heterosporous (e.g., Marsilea, Selaginella). • (vi) Like Pteridophytes many Gymnosperms show antherozoids (e.g., Cycas, Ginkgo). • (vii) Like Gymnosperms, in some Pteridophytes megaspore is retained within the megasporangium (e.g., Selaginella). • (viii) Regular alternation of sporophytic and gametophytic phase is present.