· Pteridophytes i.e. plants having feather-like leaves constitute a group of cryptogams having well developed vascular bundles.
· They are often called vascular cryptogams and Botanical snakes of the plant kingdom. i.e. non-flowering plants with vascular bundles.
· Pteridophytes are the most primitive vascular plants.
· They are mostly herbaceous and grow in moist and shady places.
· These are the plants that reproduce by spores and don’t produce the seeds. So the pteridophytes are a group of seedless vascular plants.
(Note: Seed habit was originated in selaginella due to heterospory but established in gymnosperm).
· Pteridophytes are the first vascular land plants (order Psilophytales eg: Rhynia)
· Rhynia is a fossil plant grouped under Psilophytales.
· The Carboniferous period of the palaeozoic era can be regarded as the “age of the Pteridophyta”.
· Vascular tissues are
(a) Xylem: Tracheids
(b) Phloem: Sieve cells
· All pteridophytes show sporophyte (2n) as dominant phase with distinct heteromorphic alternation of generation.
· Pteridophytes are the first plant to become sporophytic.
· The dominant generation is sporophyte which gets differentiated into root, stem and leaves.
· The roots are mainly adventitious, the main root is short-lived (ephemeral).
· Psilophytes are the pteridophytes without true roots. Instead, they have rhizoids.
· Stem is herbaceous and it has dorsiventral or radial symmetry.
· In pteridophytes, the branches of the stem don’t arise from axils of leaves.
· Leave may be small (Microphyllus) eg: Selaginella or large (Macrophyllous) eg: Fern.
· Leaves of fern are bipinnately compound.
· Large leaves of fern are called fronds.
· In some cases like Salvinia, leaves are modified into the adventitious roots.
· The vascular system is well developed i.e, these are the first plants to have well developed vascular system.
· All the vegetative parts possess the vascular tissue
· Vascular tissue is absent in the gametophyte and reproductive parts.
· In xylem; vessels and fibers are absent and in phloem, companion cells, fibres and sieve tubes are absent but sieve cells are present.
· Selaginella and Equisetum are exceptions where vessels are present.
· Cambium and secondary growth are absent (Exception: Isoetes and Botrychium).
· The gametophyte is reduced to a simple small prothallus.
· Vegetative reproduction by Rhizome, and by leaf tip in case of walking fern (Adiantum)
· Rhizome produces numerous roots called adventitious roots.
· They are most primitive vascular plants living (Selaginella, Lycopodium, Equisetum) as well as fossils (Rhynia)
· Smallest pteridophyte – Azolla
· Azolla is known as a water fern which is an aquatic fern used as a biofertilizer.
· Largest pteridophyte – Alsophila and Cyathea.
· Alsophila and Cyathea are called Tree ferns.
· Azolla is known as a water fern which is an aquatic fern used as a biofertilizer.
· Largest pteridophyte – Alsophila and Cyathea.
· Alsophila and Cyathea are called Tree ferns.
· Sporophytic plant reproduces asexually by the means of meiospore present in sporangia by sporic meiosis.
· The spore may be homosporous (same type) [Eg: Lycopodium (Club moss), Dryopteris] or may be of two different types i.e. heterosporous; Eg. Selaginella (spike moss) Salvinia, Azolla, Marsilea.
· The development of sporangium may be:
a. Eusporangiate Type: sporangium is developed from a group of cells.
Eg: Selaginella, Lycopodium, Equisetum.
b. Leptosporangiate Type: Sporangium is developed from a single cell.
Eg; Salvinia, Azolla, Marsillea.
· The group of sporangium is called sorus.
· Sori are arranged on the dorsal side of sporophyll (spore-bearing leaves) and are covered with indusium (Protective layer).
· Indusium may be formed either from the reflexed margin of leaf called false indusium; eg; in Pteris, Adiantum or from placental tissue called true indusium eg; Dryopteris.
· In Pteridium, the indusium is both true and false.
· The spores on germination give rise to flattened, dorsiventral, short-lived prothallus (gametophyte) which is monoecious in homosporous form and dioecious in heterosporous form.
· Sex organs are multicellular and jacketed.
· Sexual reproduction by antheridium and archegonium.
· Male gametes are motile and fertilization is water-dependent.
· Apogamy (Apo – without, gamy-fusion) – Formation of the sporophytic body directly from gametophyte (prothallus) without fusion of gametes.
· Apospory (Apo- without, spory- spore) – Formation of the gametophytic body directly from sporophyte without forming spores.
· Heterospory – production of two types of spores i.e.microspore and megaspore.
· Heterspory is found in a few species of pteridophytes but the majority of pteridophytes and all bryophytes are homosporous.
· Heterosporous is common in gymnosperm and angiosperm.
Types of Stele (Vascular Cylinder)
1. Protosteles· Fundamental type of stele in which vascular cylinder consists of a solid core of xylem surrounded by Phloem.
· Stele without pith.
E.g. Lycopodium (lower or primitive pteridophyte)
2. Siphonostele
Stele having pith
Types of Siphonostele:
i. Attactostele
· Scattered vascular bundles
e.g. Monocot stem
ii. Eustele
· Vascular bundles are arranged in rings.
E.g. Dicot stem also in the stem of gymnosperm.
iii. Dictostele
· It's highly divided stele e.g. fern
Dryopteris (Fern)
Systematic PositionKingdom: Plantae
Subkingdom: Embryophyta
Phylum: Tracheophyta
Subphylum: Pterosida
Class: Filicineae
Subclass: Leprosporangiatae
Order: Filicales
Family: Polypodiaceae
Genus: Dryopteris
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| Fig: Showing Different parts of Dryopteris |
· Life cycle shows distinct alternation of generation in which the main body is sporophytic (2n) and prothallus (n) represents the gametophytic generation.
· Sporophytic body of fern is initially dependent but finally independent of the gametophyte.
· Fern plant is diploid Sporophyte and sporophytic generation is dominant.
· Sporophytic body is differentiated into fibrous roots, Rhizome and leaf.
· Rhizome and Rachis of the leaf is covered by a brown hairy strand called Ramenta.
· Large size leaf of fern is called Frond.
· Leaf performs double function i.e. Photosynthetic and Spore bearing.
· Spore bearing leaf is called sporophyll.
· Leaf of fern bears sori (sing. sorus). Sori are the aggregate of the sporangium.
· Each sporangium contains a number of haploid spores which have been formed as a result of Meiosis.
· Each sorus (group of sporangia) is covered by a protective covering called the indusium.
· Inside each sporangium, 8-16 diploid spore mother cells divide by meiosis to produce 64 or lesser haploid spores.
· Wall of sporangium is differentiated into
a. Annulus (thick-walled)
b. Stomium (thin wall)
Breaking of sporangium occurs from stomium with the help of Annulus.
Note: Moss capsule breaks from the annulus.
· Spores on germination form prothallus.
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| Fig: Showing T.S of sorus |
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| Fig: Showing single sporangium |
PROTHALLUS
· A haploid, heart-shaped, Gametophytic (n) stage in the life cycle of Fern· Green and photosynthetic (autotropic) with unicellular rhizoids.
· Ventral or undersurface of prothallus bears antheridia and archegonia
· Antheridium is the sessile spherical or oval body that contains many Antherozoid mother cells. The antherozoid mother cells produce spirally coiled Multiflagellated antherozoids.
· Archegonium is a flask-shaped structure with a swollen basal portion (venter) and a slender tube-like portion (neck). It is oblique with a single binucleate neck canal cell.
Archegonia [egg cell (venter) – venter canal cell – Neck canal cell – Neck cell]
· At the time of fertilization mucilage and Malic acid secreted by archegonia attract the antherozoid towards it. (Chemotactic movement)
· Fertilization results in the formation of a zygote or oospore (2n).
· Fern shows distinct Heteromorphic alternation of generation.
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| Fig: Showing fern prothallus |
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| Fig: Showing Life cycle of fern |
High Yielding Points from Pteridophyte
1. In the prothallus of fern Rhizoids and sex organs are on the ventral surface and is protandrous.2. Among the pteridophytes vessels are found only in Selaginella and Equisetum.
3. Among the pteridophytes, Secondary growth occurs only in Isoetes.
4. In Selaginella male gametes are biflagellated (while in most of the pteridophyte, multi-flagellated is found. @BISEL.
5. In Pteris, Coenosorous and false indusium occur.
6. Due to the phenolic compound (that makes it bitter) Phlobaphene, animals do not graze on fern.
7. In prothallus, antheridium is present near the rhizoids (@ d = d) and the archegonium is near the apical notch (@ n = n)
8. Seleginella is Eusporogiate.
Also, Read Notes of Other Lessons of Botany: