define pteridophyta in points.
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Answer:
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1.the pteridophytes are the first land plants which have vascular tissues.
2.these are green autrotrophic plants.
3.the plant body is differentiated in roots, stem and leaves.
4.vasculae tissues are present.
5.s.e. x organs are multicellular.
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Answer:
PTERIDOPHYTA:
- Pteridophytes are plants with Feather like Leaves.
- Pteridophytes are a group of primitive land plants belongs to the Cryptogams.
- They are the first evolved plant group with vascular tissue system for the conduction of water and food materials.
- Due to the presence of vascular tissue, they are called as Vascular Cryptogams. The term Pteridophyte is derived from two words ‘Pteron’ meaning feather and ‘phyton’ meaning plant.
- Thus, Pteridophytes are the plants with Feather-like leaves. Pteridophytes occupy the intermediate position between Bryophytes and Phanerogams (seed plants).
- The important characteristics of Pteridophytes are summarized below:
Pteridophyta General Characters
Ø The division Pteridophyta includes primitive living and fossil vascular plants.
Ø They were originated in the Silurian period and flourished in the Devonian period.
Ø They are known as ‘Vascular Cryptogams’ – cryptogams with vascular system.
Ø They show heteromorphic alternation of generation with prominent Sporophytic and Gametophytic phases.
Ø The main plant body of Pteridophyte is the sporophytic plant (diploid).
Ø The gametophytic and sporophytic generations are two independent plants (not physically connected).
Habit and Habitat of Pteridophytes
Ø Pteridophytes show much variation in form, size, and habitat.
Ø Most of the present day Pteridophytes are annual, terrestrial and herbaceous plants. (Example: Psilotum, Selaginella Lycopodium).
Common Pteridophytes
Ø Some are large perennial trees- Example Angiopteris, Alsophila
Ø Some Pteridophytes are aquatic (Example- Azolla, Marsilea, Isoetes, Salvinia)
Ø Few Pteridophytes are xerophytes (Example- Selaginella lepidophylla called Resurrection plant)
Ø Few are halophytes (Example- Acrostichum)
Stem, Root and Leaves of Pteridophytes
Ø The sporophytic plant body is differentiated into stem, root and leaves.
Ø Stem and roots have the permanent growing region at the apex.
Ø Most of the present day Pteridophytes are with herbaceous stem, some are woody.
Ø The stem is usually branched; the branching may be monopodial or dichotomous.
Ø Branches do not arise from the axils of leaves.
Ø The primary roots are ephemeral (short-lived) and they are immediately replaced by adventitious roots.
Ø The photosynthetic tissue is mostly restricted to the leaves.
Ø Based on the size, three types of leaves are found in Pteridophytes:
(1). Scale leaves: small minute scale-like leaf, Example- Equisetum
(2). Small sessile leaves: leaves are small without leaf stack (petiole), Example- Lycopodium, Selaginella
(3). Large, petiolate compound leaves: occurs in true ferns, Example- Pteris, Angiopteris
Scale Leaves and Foliage Leaves
Ø In ferns, the young leaves show Circinate Vernation
Ø Circinate vernation: young leaves are curved inward, typically found in higher Pteridophytes and in some primitive Gymnosperms.
Circinate vernation Definition
Ø Based on the internal structure of leaves, the Pteridophytes are classified into groups:
(1). Microphyllous Pteridophytes:
@. Leaves are small and simple
@. Leaves possess a single vein at the middle region
@. No leaf gap formation in the stem
@. No tissue differentiation in the leaf
@. Example- Lycopodium, Selaginella
(2). Macrophyllous Pteridophytes:
@. Leaves are large and compound, usually pinnatifid
@. Venation is complex
@. Mesophyll is differentiated into palisade and spongy tissue
@. They form prominent leaf gap in the stele of stem
@. Example- Pteris
Ø Leaves and stem also possess many trichomes or hairs.
Ø Stomata are present and they are distributed on both upper and lower surface of the leaves.
Vascular Tissue in Pteridophytes
Ø Vascular elements are well developed in Pteridophytes.
Ø Root and stem possess well developed vascular system composed of xylem and phloem.
Ø There is a progressive advancement of vascular structure in different groups of Pteridophytes
Ø Vascular structures are commonly called as ‘stele’.
Ø Stele may be:
(1) Protostele: stele without pith (Lycopodium)
(2) Siphonostele: stele with centrally placed pith (Equisetum)
(3) Dictyostele: stele with leaf gaps (Pteris)
(4) Polystele: stele is differentiated into many vascular strands (Angiopteris).
Learn more: Stelar System in Pteridophytes
Ø Cambium is absent in the vascular tissue and thus no secondary thickening occurs.
Ø Some Pteridophytes such as Isoetes show secondary growth.
Ø The xylem chiefly composed of tracheids and very few parenchyma.
Ø Xylem vessels are completely absent.
Ø The phloem is made up of sieve cells and phloem parenchyma.
Ø Companion cells are absent in the phloem of Pteridophytes.