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Pteris : features, anatomy, morphology and lifecycle

The document provides a comprehensive overview of the Pteris fern's classification, distribution, habitat, morphology, anatomy, reproduction, and life cycle. It details the characteristics of various plant structures including roots, rhizomes, leaves, and spores, as well as the processes of fertilization and embryonic development. Pteris is highlighted as a homosporous fern with distinctive reproductive structures and a unique gametophyte generation.

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PTERIS
CLASSIFICATION  Division : Filicophyta  Class : Leptosporangiopsida  Order : Filicales  Family : Polipodiaceae
DISTRIBUTION  It is a cosmopolitan fern distributed almost all geographical region.  It is represented by about 250 species that grown abundantly in the tropical and sub tropical regions of the world.  Common species in India : P.vitata , P. cretica L, P.stenophylla wall, P. wallichiana etc.
HABITAT  It is usually grown in well drained places or crevices of rocks.  It is common along slopes of hills and seen 1200m above sea level.  They are a terrestrial genus inhabiting shady and moist forests and hilly areas.
Morphology  The main sporophytic plant body is differentiated into, - Root - Rhizomatous stem - Leaves
ROOTS  Roots are black, slender and wiry arising from the underside of the Rhizome.  The primary root is ephemeral, and is replaced by a large number of adventitious roots developed all over the surface of the rhizome.  The roots are small and branched.
RHIZOMATOUS STEM  The rhizome or stem may be creeping (P. grandiflora) or erect (P. cretica, P. vittata) which may or may not show branching.  The rhizome is differentiated into nodes and internodes and its entire surface is covered with scales.  The growing point of rhizome is covered with ramenta.
LEAVES  The leaves are borne on the upper surface of the Rhizome.  Leaflet is rough, has a midrib from which lateral veins with dichotomous branching arise. Venation is open dichotomous venation.  When young the leaves are spirally coiled and show circunate vernation that is typical of true ferns.  The leaves are unipinnately or multipinnately compound or decompound with a long rachis.  Developed leaves are called fronds.
 Petiole is covered with scales and hairs  The pinnae are sessile. The pinnae are small near the base as well as towards the apex, while they are large towards the middle.  Leaf apex is occupied by an odd leaflet.  Leaflet is rough, has a midrib from which lateral veins with dichotomous branching arise. Venation is open dichotomous venation.  Each pinna is transversed by a central midrib which gives off lateral veins that bifurcate near the tip.
 Leaf bears reproductive structures called sori, along the ventral margin of their pinnae.  Sori are continuous along the margin , except the apices.
ANATOMY  Rhizome  Leaf  Petiole  Root
1. Rhizome Rhizome is differentiated into epidermis, cortex and stele. Epidermis  Single layered and invested with a hard and protective cuticle around.  In some growing young parts, it may be covered by ramentum. Cortex  Multilayered  It forms main bulk of the Rhizome .
 It is differentiated into, 1. Outer cortex 2. Inner cortex  Outer cortex is sclerenchymatous and it forms the hypodermis.  Inner cortex is parenchymatous.  Endodermis is uniseriate
Stele  Stelar organization of the Rhizome varies with species. - Solenostelic - Dictyostelic  A stele in which the protostele is medullated or with pith at the centre is Known as siphonostele.  In siphonostele , pith is found with one leaf gap.  Siphonostele that is broken into a network of separate vascular strands are called dictyostele. This breaking is due to the presence of large number of leaf gaps.  Each separate vascular strands is called meristele.
Stele  Stele consists of number of meristeles usually arranged in two rings inner and outer.  Meristele is embedded in the parenchymatous ground tissue.  Each meristele is elliptical with single layered endodermis having casparian strips in its radial walls.  1- 2 layered thin walled pericycle is present below the epidermis and surrounding the phloem.  Phloem has only sieve cells and phloem parenchyma. It completely surrounds the xylem.  Xylem is present at the centre of the meristele. It shows central protoxylem surrounded on either side by metaxylem.
2. ANATOMY OF PETIOLE  It is differentiated into epidermis, ground tissue and vascular bundle. Epidermis  Single layered with narrow quandrangular cells covered by thick cuticle.  Some epidermal cells give rise uniseriate bicellular hairs called as ramenda Ground tissue  It has multi layer sclerenchymatous hypodermis followed by parenchymatous tissue in which the vascular bundle is empeded.
Vascular bundles  It is ‘ V’ or ‘ U’ shaped  It resembles meristele and has single layered endodermis with casparian strips.  Pericycle is 1 or 2 layered and parenchymatous.  Xylem is at the centre with mesarch condition surrounded by phloem.
ANATOMY OF LEAF  Anatomically leaves has three main parts namely upper epidermis , lower epidermis and mesophyll. Epidermis  The cells of the upper epidermis are large with thick outer walls while those of the lower epidermis are small and thin walled.  Stomata are restricted to the lower epidermis. Mesophyll  It is either homogeneous or differentiated into upper pallisade and lower spongy with broader intercellular spaces.
 Midrib region has a single concentric type of vascular strand with the distinct endodermis.  Bundle sheet extensions are prominent and they occur as groups of thick wall the cells below the upper and above the lower epidermis.  Palisade and spongy tissues are absent around the midrib
ANATOMY OF ROOT Root has 4 main anatomical parts namely epidermis, cortex, endodermis and stele. Epidermis  It is single layered with thin walled cells.  A few cells form root hairs Cortex  It is multilayered and differentiated into paranchymatous outer cortex, sclerenchymatous inner cortex and single layered endodermis with casparian thichenings  Endodermis is single layered.
Stele  It has single layered thin walled pericycle  Exarch or diarch xylem  Protostele
REPRODUCTION  Vegetative  Asexual
VEGETATIVE REPRODUCTION  Death and decay of older portion of Rhizome.  When did decay reaches the branching regions the two branches separate and grow us individual plants.
SPORE PRODUCING ORGAN  Pteris is a homosporous fern  The sorus of pteris is called coenosorus.  Coenosorus are marginal , born continuously on sporophyll margins.
 The coenosori are protected by the reflexed margin ( the false indusium) of pinnae.  Sori are intermingled with many sterile hairs in between the sporangia
Structure of a mature sporangium  A mature sporangium has a long stalk that terminates in a capsule.  The jacket or wall of the capsule is single layered but with three different types of cells.
1. A thick walled vertical annulus incompletely overarches the sporangium. 2. A thin walled radially arranged stomium. 3. Large parenchymatous cells with undulated walls.
 The sporangium dehisces transversely along the stomium due to the shrinkage of annular cells  The spores are dispersed through air to a moderate distance.
 The capsule contains many spores. All spores are structurally and functionally alike ; hence pteris is a homosporous pteridophyte.  Spores are triangular in shape with the trilete aperture, bounded by two walls , exine is variously ornamented.  The spores germinate after falling on a suitable subtractum. Initially the spore wall ruptures and the inner contents come out in the form of a germ tube and subsequently by a transverse division in the germ tube forms the first prothallial cell. From that the complete gameatophyte is orginated.
GAMETOPHYTE  Green , heart shaped with many rhizoids on the under side for the absorption.  The prothallus is made up of parenchymatous cells which are single celled thick towards the margin and many celled thick towards the centre  The growing point are located in the apical notch.  The prothallus is monoecious.  Antheridia appear first and are confined to the basal central or lateral regions among the rhizoids  Archegonia develop near the apical notch.
ANTHERIDIUM  A mature antheridium consists of two ring cells, one or two cover cells and a central mass of coiled and multinucleate antherozoids.  The antheridium at the maturity absorbs water and swells.  Due to the increase in pressure within the antheridium the cover cells split apart releasing the antherozoids in a thin film of water present on the surface of the prothallus.
ARCHEGONIUM  It consists of a swollen base called Venter and a projecting short and slender neck.  A mature archegonium of pteris consists of a 5-6 celled projecting curved neck , a neck canal cell, a ventral canal cell and an egg.
FERTILIZATION  At this time the ventral canal cell, the neck canal cell and the neck cell at the top disintegrate forming an open passage for the antherozoids to come towards the egg and eventually one of the antherozoids fuses with the egg to form the zygote.
New sporophyte ( Embryo)  In pteris the first division of zygote is vertical followed by a second transverse division resulting in the formation of a quadrant. Further a 32 celled embryo is formed due to further divisions of the quadrant.  The differentiation of embryo begins at this 32 celled stage. No suspensor is formed the hypobasal cells form stem apex and foot, while epibasal cells form cotyledon and root.
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