Pteridophytes Student's Copy PDF

# Pteridophyta ## PTERIDOPHYTE * The term pteridophyte is derived from two Greek words **Pteron** means feather and **phyton** means plant. * Thus, pteridophytes are the plants with feather like leaves. * Pteridophytes are the first terrestrial vascular plants. * They occupy a transitional positi...

# Pteridophyta ## PTERIDOPHYTE * The term pteridophyte is derived from two Greek words **Pteron** means feather and **phyton** means plant. * Thus, pteridophytes are the plants with feather like leaves. * Pteridophytes are the first terrestrial vascular plants. * They occupy a transitional position between bryophytes and spermatophytes. * Pteridophytes do not produce flowers and seeds (cryptogams) but are the first land plants having vascular tissues (xylem and phloem). So, they are also called **vascular cryptogams**. ## Characteristics of Pteridophytes: * They mostly grow on moist and shady places. * The main plant body is _sporophytic_ and differentiated into root, stem and leaves. * They are considered as the first living plant evolved on land. * They are known as vascular cryptogams (flowerless, seedless but have vascular tissues except xylem vessels and companion cells). * Some pteridophytes have small leaves called _microphylls_ (Example: Lycopodium) and some other have large leaves called _megaphylls_ (Example: Pteris). * Plants (sporophyte) reproduce by spores formed in sporangia. Sporangia develop either on the ventral side of leaves or in the axil of leaves. Such leaves are called _sporophylls_. * Spores may be homosporous or heterosporous (the small microspores and the large megaspores). ## Sometimes sporophylls form compact structures called cone or strobili. * Spores germinate to give rise to a multi-cellular, gametophytic, chlorophyllous and independent body called prothallus - a thalloid structure. * Sex organs are multicellular and jacketed. The male sex organs are called _antheridia_, while the female sex organs are called _archegonia_. * Water is essential for fertilization as male reproductive units are motile. * An embryo develops _in situ_ after fertilization and the sporophyte remains attached to the gametophyte till the development of root. * Plants show clear alternation of generations. The sporophyte and gametophyte are independent of each other. ## Parts of a Fern The image shows a diagram of a fern with the following parts labelled: * _Blade_ - the flattened section of the frond * _Frond_ - the complete leaf * _Pinna_ - a primary leaflet * _Rachis_ - the stalk within the blade * _Costa_ - the main vein running through the blade * _Pinnule_ - a division of the pinna * _Stipe_ - the stalk of the frond ## Diagram of Fern Another diagram shows the following parts of a fern: * _Frond_ - the complete leaf * _Blade_ - the flattened section of the frond * _Pinna_ - a primary leaflet * _Pinnule_ - a division of the pinna * _Pinnulet_ - a finer division of the pinna * _Midrib, Axis, Rachis_ - the stalk within the blade * _Stipelet_ - a small stalk * _Stipe_ - the stalk of the frond * _Rhizome_ - the underground stem * _Roots_ - the root system ## Morphology of Dryopteris: The image shows a labelled diagram of a Dryopteris fern. * _Habitat_ - commonly found in moist and shady places in tropical to temperate regions. Some are found in aquatic habitat and some are _epiphyte_ (growing on trunk of trees) * _Systematic position_ * Kingdom: Plantae * Division: Pteridophyta * Class: Pteropsida * Order: Filicales * Family: Polypodiaceae * Genus: Dryopteris * _Frond_ - the whole fern leaf, blade and stalk * _Blade_ - the expanded leafy part of the frond * _Axis - rachis_ - the stalk within the blade * _Pinna - leaflet_ - a primary division of the blade * _Pinnule - subleaflet_ - a division of the pinna * _Pinnules_ - can be divided into lobes. * _Stalk - Stipe_ - the stalk below the blade * _Rhizome_ - the underground stem * _Root_ - the root system * _Fiddlehead (Crozler)_ - an uncurling frond ## The plant body is _sporophytic_ and differentiated into root, stem, and leaf. * **A. _Roots_**: The root is fibrous and arises from stem. The roots are short lived and therefore called _ephemeral_ and branched. * **B. _Stem_**: The stem is underground, dark brown and horizontally placed, branched or unbranched. It is called _rhizome_. It is covered by brownish scales called _ramenta_ which protects young leaves from the injury and drying. * **C. _Leaf_**: The leaf is in aerial part. It consists of thick and stout _petiole_. On the either side of _rachis_, pinnae are present. The young leaves are curved and called _circinate_ leaves. ## Reproduction: Reproduction in Dryopteris takes place by three methods: vegetative, asexual and sexual methods. ### A. Vegetative reproduction: It takes place by following methods. * **Fragmentation:** In Dryopteris repens, the rhizome separates into fragments by the progressive death and _decay_ of older parts. Each of the fragments develops into new independent plants. * **Adventitious buds:** Adventitious buds arise in the axil of leaves which detach from the plant and form new plants. * **Apogamy:** It is the formation of new sporophyte directly from the gametophyte. Such a new sporophyte is haploid. ### B. Asexual reproduction: It takes place by formation of meiospores. Dryopteris bears a number of sori on the lower side of leaves. Each sori bears homosporous spores inside sporangium. The sporangia of sorus are protected inside the kidney shaped structure called true indusium. * **Sporangium:** Each mature sporangium have a long, slender and multicellular stalk and biconvex capsule. Capsule of sporangium bear _spore mother cells_ that undergo meiosis to form about 48 haploid spores. At the edges it consists thick radial cells called _annulus_. Annulus does not form complete ring due to presence of larger, thin walled cells called _stomium_. Two cells of stomium are more elongated than others called as _lip cells_. ### Dehiscence of sporangium: As the spores mature, the indusium dries up and shrivels. The exposed sporangia dehisce from the region between two lip cells of stomium due to contraction of annulus. The spores are thrown out violently and dispersed by air currents. ### Germination of spores: The spores are minute and blackish brown with uninucleated protoplast having reserve food and cell organelles. * After falling on suitable soil, the spores germinate to from flattened, green thalloid gametophyte called _prothallus_. ### Mature gametophyte (prothallus): The prothallus is heart shaped, multicellular, chlorophyllous, independent and autotrophic structure that grows in moist and shady places. The ventral surface of prothallus consists brown tubular rhizoids and male and female sex organs. It is more than one cell layer thick at the centre called cushion. ### C. Sexual reproduction: The prothallus of Dryopteris is monoecious bearing both sex organs male antheridia and female archegonia. * **Antheridium:** The antheridium is small, sessile and multicellular organ on the ventral surface of prothallus that consists a semi transparent jacket layer (with two ring shaped cells and one or two cap cells) enclosing the _androcytes_. Each androcyte divide mitotically and metamorphoses to form spirally coiled, uninucleated, _multiciliated_ and motile gametes called antherozoids / spermatozoid. The antheridium absorbs dew or rain water and swells up pushing cap cell. Thus, it breaks and release antherozoids that swim in water. * **Archegonium:** It is a female reproductive organ that appears in a cluster of 4-12 numbers behind the apical notch. The mature archegonium is sessile, flask shaped multicellular structure with a swollen _venter_ and a short curved neck with single binucleated neck canal cell. The venter is deeply sunken in the tissue of prothallus. It contains an egg and a small venter canal cell. The venter of archegonium does not have jacket but neck has jacket of four vertical rows of cells. ### Fertilization: As the archegonium matures, the contact wall of venter canal cell and neck canal cells along with the tip of neck disorganizes and form mucilage containing malic acid. These substances ooze out from the mouth of archegonium. The antherozoids from antheridium swim in water as they are attracted by malic acid and enter through the passage. One of the antherozoids reach ovum to fertilize it. Hence, the zygote is formed. ### The embryo (sporophyte): The diploid (2n) zygote (oospore) divides mitotically to form 8 celled embryo (4 epibasal cell towards notch and 4 hypobasal cell towards the posterior end). The four cells of epibasal half form stem and cotyledon while the four hypobasal half produce root and foot. The foot takes part in fixing the young plant to the gametophyte and _also_ absorbs food from the prothallus. When root grows downward in soil, sporophyte become independent and foot and prothallus gradually disintegrates. Hence, an independent fern plant is developed. ### Alternation of generation: The main plant of Dryopteris is independent, diploid (2n) sporophyte that bears sporangia. Haploid (n) spores are produced from sporangia during asexual reproduction. The spores germinate to give rise to gametophyte (the prothallus) which later produces sporophytic plant body from zygote. Hence, the formation of haploid gametophyte and diploid sporophyte takes place one after another in a single life cycle, which is known as alternation of generation. ## Economic Importance of Pteridophytes: * **(1) Food:** Sporocarps of Marsilea, a water fern, yield starch that is cooked and eaten by certain tribal. * **(2) Soil Binding:** By their growth pteridophytes bind the soil even along hill slopes. The soil is protected from erosion. * **(3) Scouring:** Equisetum stems have been used in scouring (cleaning of utensils) and polishing of metals. Equisetum species are, therefore, also called scouring rushes. * **(4) Nitrogen Fixation:** Azolla (a water fern) has a symbiotic association with nitrogen fixing cyanobacterium Anabaena azollae. It is inoculated to paddy fields to function as biofertilizer. * **(5) Medicines:** An anthelmintic drug is obtained from rhizomes of Dryopteris (Male Shield Fern). * **(6) Ornamentals:** Ferns are grown as ornamental plants for their delicate and graceful leaves. _Ruhmora adiantiformis_ is called the florist's fern; since their leaf resists wilting they are used in the cut flower arrangements. * **(7) Handicrafts:** Some of the ferns are used in handicrafts; petioles of certain ferns are used for making basketry and bracelets. * **(8) Dye:** Pteridium leaves are used for making the green dye. * **(9) Dry industrial lubricant:** Club mosses (some Lycopodiopsida) are used as a dry industrial lubricant since its microscopic spore contains non-volatile oils. The spores are also used as flash powder in photography and also as finger print powder in forensic investigation. * **(10) Noxious weed:** Some members of pteridophytes are noxious weed like Salvinia, Pteridium which are weedy aquatic ferns.