What are Pteridophytes?
- The term 'Pteridophyta' was proposed by Haeckel.
- The study of pteridophytes is known as pteridology.
- Pteridophytes are known as reptiles of the plant kingdom.
Examples of Pteridophytes
- Pteridophytes are also called as vascular cryptogames. Pteridophytes are vascular plants, i.e. xylem and phloem, are present in it. In pteridophytes, vessels in xylem and companion cells in phloem are absent.
- But exceptionally xylem of Pteridium, Selaginella and Marsilea contains false vessels. These false vessels are formed by the modification of tracheids, so false vessels are tracheids.
Type of vascular bundle:
(iii) Mesarch condition and closed.
Note: Secondary growth is absent (due to absence of cambium) in pteridophytes but exceptionally secondary growth is present in stem of Isoetes.
Characteristics of Pteridophytes
- Pteridophytes are called the first successful terrestrial plants, i.e. they are more adapted terrestrial plants as compared to bryophytes because:
(i) Vascular tissue is present in pteridophytes.
(ii) They have roots.
- Pteridophytes are not completely successful terrestrial plants because they need water for fertilization, so pteridophytes grow in shady and moist places.
- In Pteridophyta, the plant body is completely differentiated into root, stem and leaves; hence their body is called a cormophyte.
- The primary root remains alive for short period. After some time it is replaced by adventitious roots.
- The stem is erect or prostrate. In some pteridophytes, the stem is underground, which is known as the rhizome.
Classification of Pteridophytes
- On the basis of leaves, pteridophytes are of two types:
1. First, in which stem is smaller while leaves are larger. They are known as macrophyllous Pteridophytes.
Example: Pteridium, Pteris, Marsilea.
2. Second, in which stem is larger and leaves are smaller. They are called as microphyllous Pteridophytes.
Example: Equisetum, Lycopodium, Selaginella
- Pteridophyta is classified into four main classes:
The most ancient vascular plants are placed in this class. The plants in this class have many primitive characters:
- Their plant body is differentiated into stem, scaly leaves and rhizoids.
- Rhizoids are present instead of roots. In psilopsida, the stem is underground, i.e. rhizome. This rhizome bears some aerial branches. Sporangia are formed on these branches.
Note: Vascular tissue is present only in stem.
- Tropophylls are absent, scaly leaves are known as cataphylls (Scaly leaves - dry, brown coloured and non-photosynthetic. They are only for the protection of sporangia).
- Their leaves do not have the capacity for photosynthesis, therefore photosynthesis is done by stem.
- Sporangia are formed on the stem. Sporophylls are absent.
- Most of the plants in this class are extinct.
- Only one living genus is present in this class:
- Psilotum → A living fossil Rhynia and Horneophyton – Fossil plants
2. Lycopsida or Lepidophyta or Microphyllophyta
- Club mosses are placed in this class.
- The plant body of club mosses is differentiated into root, stem and leaves. Club mosses are microphyllous, i.e. small green leaves are present on the stem. Leaves of club moss are unnerved i.e. the only midrib is present.
- Roots are adventitious.
- Sporangia are formed on sporophylls. These sporophylls are not scattered on the stem, instead, they are present in groups at the tip of the plant. These groups are called as strobilus or cone. The strobilus of club mosses is loose and small.
Note: In Lycopsida tropophylls and sporophylls are separate. Tropophylls are present whole year while sporophylls are formed during reproduction. Sporophylls are present at the tip of plant in group and form cone (cone is photosynthetic structure)
- Lepidodendron - Giant club moss – fossil plant
- Lycopodium - Common club moss or Ground pine or Trailing evergreen. It is a medicinal plant. It is used as a tonic in Homeopathic medicines.
- Isoetes - Quill wort or Merlyn grass – Aquatic weed.
- Selaginella - Little club moss or spike moss or Bird's nest moss Resurrection plant - Some species of Selaginella are known as "Drought Escapers," i.e. do not face drought condition, they complete their life cycle in a short wet season. In dry season plant dries and rolls in ball-like structures.
- In this stage, it passes out dry season. When the wet season returns plant absorbs water and again becomes normal green plants. So, it is also known as "resurrection plant".
- Selaginella bryopteris: It is known as "Sanjeevani" - No medicinal properties.
3. Sphenopsida or Arthrophyta or Calamophyta
- In this class, Horse tails are included.
- The plant body of horse tails are differentiated into root, stem & leaves.
- Their stem is modulated, i.e. stem distinctly differentiated into node and internode. Scaly leaves are present on these nodes.
- Silica is present in the epidermis of stem and leaves. Due to silicated surface, leaves become rough. If two horse tail plants collide, then there is a dangerous chance of fire in the forest.
- The formation of sporangia takes place on special branches of stem called as sporangiophores.
- Sporangiophores are arranged in a group and form a long and condensed cone. This cone is formed at the apical part of aerial stem.
EquisetumExample: Equisetum (Pipe), Sphenophylla, Hyenia.
- This is the largest group of pteridophytes.
Parts of a Fern
- They are commonly called as ferns. Most of the pteridophytes are ferns.
- Ferns are megaphyllous (macrophyllous), i.e. stem is small and leaves are comparatively larger and these leaves are known as 'Fronds'. Leaves are multinerved.
- Multicellular hair are present on the young leaf and young stem of ferns which are called as ramenta. They are for protection.
- There is no difference between tropophylls and sporophylls in fern, i.e. every leaf of fern forms sporangia at the time of reproduction. Therefore cones are not produced in ferns.
Example of Ferns
Life Cycle Of Pteridophytes
- Pteridium ➜ They are called "Bracken fern" or "Sun fern"
- Pteris ➜ They are called "Bracken fern" or "Sun fern."
- Dryopteris ➜ They are called "Bracken fern" or "Sun fern."
- Adiantum ➜ Walking fern or Maiden hair fern This name is given to them due to rapid vegetative reproduction. Vegetative reproduction in Adiantum takes place by means of leaf tip. It spreads very fast.
- Dryopteris ➜ Also called as Brook shield fern.
- Osmunda ➜ Royal fern or flowering fern
- Ophioglossum ➜ Adder's tongue fern
- Marsilea ➜ Pepper wort fern
- Azolla ➜ Aquatic fern (Smallest pteridophyte and biofertilizer)
- Onychium ➜ Golden fern
- Cyathea ➜ Lofty tree fern
- Alsophila ➜ Tree fern (Largest pteridophyte)
- Cheilanthes ➜ Silver fern
- Botrychium ➜ Moonwort fern
- The plant is sporophyte. i.e. diploid.
- Most of the pteridophytes are homosporous, i.e. only one type of spores are formed during reproduction.Example: Lycopodium, Pteridium, Equisetum, Dryopteris.
Try yourself:Dominant generation in pteridophytes is
Main plant body of pteridophytes is sporophyte which is diploid.
- Exception: Some Pteridophytes are heterosporous, i.e. two types of spores microspores and megaspores.
Example: Selaginella, Isoetes, Marsilea, Salvinia, Azolla, Stylites, Pillularia, Regellidium.
- Formation of spores takes place in sporangia. Sporangia are formed at the abaxial surface of leaves.
- The leaves on which sporangia are formed are called sporophylls (reproductive leaves) and normal photosynthetic leaves are called tropophylls (vegetative leaves). Sporangia are present in groups, these groups are called sorus. Many sorus are found on sporophylls. The groups of sorus are called sori.
Reproduction in Pteridophytes
- In Pteridophyta, sporophylls are also photosynthetic. This is a unique character of Pteridophyta.
- In pteridophytes development of sporangia takes place by two methods:
(i) Leptosporangiate: Each sporangium develops from single initial cell.
(ii) Eusporangiate: Each sporangium develops from a group of initial cells.
- Leptosporangiate is advanced character because all higher pteridophyte are leptosporangiate.
- Spore mother cells are present in sporangia. Spores are formed in these spore mother cells by meiosis and these spores start the gametophytic generation.
- In Pteridophyta, the germination of spores is exosporic, i.e. germination takes place outside the sporangia (in soil).
- In soil, a gametophyte is formed by the germination of each spore, which is known as prothallus. The formation of gametophyte takes place in the soil therefore, it is free (independent) and autotrophic.
- There is no relation between the main sporophytic plant and prothallus. Prothallus (gametophyte plant) is made up of thallus and rhizoids. It is non-vascular.
Note: In plant kingdom, the gametophyte is always non-vascular.
- Prothallus (gametophyte) is monoecious, but in heterosporous pteridophytes prothallus is dioecious.
In heterosporus pteridophytes:
Microspores form - Male gametophyte
Megaspores form - Female gametophyte
- The formation of sex organs takes place on this gametophyte. Male sex organs are called as antheridium and female sex organs are called as archegonium. The formation of male gametes takes place in Antheridia, which are called antherozoids.
- Antherozoids are spiral and multiflagellate but exceptionally antherozoid of Selaginella are spindle-shaped and in Lycopodium is curved (comma) and biflagellate. Egg is formed in archegonium.
- Fertilization takes place by zoodiogamy and zygote is formed as a result of fertilization. Zygote develops and forms an embryo. Now, this embryo develops and forms a sporophytic plant with root, stem, leaf.
Type of sexual reproduction in pteridophyta is oogamous.
Their life cycle is diplo-haplontic type.
The unique character of life cycle of Petridophyte is - Independent alternation of generation i.e. sporophyte and gametophyte are independent of each other.
Try yourself:Azolla is used as a biofertilizer because it
Azolla is used as a biofertilizer because it has association of cyanobacterial members in their internal tissue. Cyanobacaterial members can fix atmospheric nitrogen.
Some Important Points
- Vivipary is present in it, i.e. partial endosporic germination. Seed habit was originated inSelaginellalike pteridophytes.
- Ligulate leaves (tongue-shaped) are present in it Function - Ligule is secretory structure, which secretes water and keeps the sporangium and the young leaf moist.
- In some pteridophytes, sporangia are not formed on lower surface of sporophylls.
- In some pteridophytes, sporangia are formed at the axil of leaf.
- In some pteridophytes, sporangia are formed in spike.
- In some pteridophytes, sporangia are formed in sporocarp.
Example: Marsilea, Azolla
(iii) Habitat of Some Important Pteridophytes
- Most of the pteridophytes are found in moist soil and shady places.
- Aquatic: Some pteridophytes are found in water.
Example: Marsilea, Salvinia, Azolla, Isoetes.
- Epiphytes: Some pteridophytes grow on other plants.
Example: Lycopodium phlegmeria, Ophioglossum pendulum, Pleopeltis.
- Xerophytes: Some pteridophytes are found in deserts.
Example: Selaginella rupestris, Selaginella bryopteris, Selaginella lepidophylla.