Pteridophytes — Revision Notes

⚡ 30-Second Revision

First vascular plants: — Possess xylem and phloem.
Dominant Sporophyte: — Diploid ($2n$), independent, photosynthetic.
Gametophyte (Prothallus): — Haploid ($n$), small, independent, photosynthetic, bears sex organs.
Reproduction: — By spores (produced in sporangia).
Fertilization: — Requires water (motile antherozoids).
Homosporous: — One type of spore (e.g., most ferns, *Lycopodium*).
Heterosporous: — Two types of spores (microspores, megaspores; e.g., *Selaginella*, *Salvinia*).
Classes & Examples:

- Psilopsida: *Psilotum* - Lycopsida: *Lycopodium*, *Selaginella* - Sphenopsida: *Equisetum* - Pteropsida: *Dryopteris* (ferns)

Key terms: — Sporophyll, Strobilus, Sori, Indusium, Rhizome.

2-Minute Revision

Pteridophytes are the pioneering vascular plants, marking a significant evolutionary step with their true roots, stems, and leaves, and a functional vascular system. Their life cycle is dominated by the diploid sporophyte, which is the familiar plant body, independent and photosynthetic.

This sporophyte produces haploid spores via meiosis in sporangia, often found in clusters called sori (in ferns) or within cone-like strobili (in clubmosses and horsetails). These spores germinate into a small, independent, photosynthetic haploid gametophyte, known as a prothallus.

The prothallus bears antheridia (male) and archegonia (female) sex organs. Fertilization is water-dependent, with motile antherozoids swimming to the egg, forming a diploid zygote that develops into a new sporophyte.

Pteridophytes can be homosporous (one type of spore, e.g., most ferns) or heterosporous (two types of spores: microspores and megaspores, e.g., *Selaginella*), with heterospory being a crucial precursor to the seed habit.

They are classified into Psilopsida (*Psilotum*), Lycopsida (*Lycopodium*, *Selaginella*), Sphenopsida (*Equisetum*), and Pteropsida (ferns).

5-Minute Revision

Pteridophytes represent the first group of plants to successfully colonize terrestrial environments more extensively than bryophytes, primarily due to the evolution of a vascular system (xylem and phloem).

This allows for efficient transport of water and nutrients, supporting true roots, stems, and leaves. Their life cycle is characterized by a dominant, independent, and photosynthetic sporophyte ($2n$) generation.

This sporophyte produces haploid spores ($n$) through meiosis within sporangia. These sporangia are often located on specialized leaves called sporophylls, which can be scattered or aggregated into compact structures called strobili (e.

g., in *Lycopodium*, *Equisetum*). In ferns (Pteropsida), sporangia are typically found in clusters called sori on the underside of fronds, often protected by an indusium.

Upon germination, a spore develops into a small, independent, and photosynthetic haploid gametophyte ($n$), also known as a prothallus. This prothallus bears the male sex organs (antheridia, producing motile antherozoids) and female sex organs (archegonia, producing an egg).

Fertilization is external and strictly requires a film of water for the antherozoids to swim to the egg. The resulting diploid zygote ($2n$) develops into an embryo, which then grows into a new sporophyte, completing the cycle.

Pteridophytes exhibit two reproductive strategies: homospory, where only one type of spore is produced (e.g., most ferns, *Lycopodium*), leading to bisexual gametophytes; and heterospory, where two distinct types of spores (microspores and megaspores) are produced (e.g., *Selaginella*, *Salvinia*), leading to unisexual male and female gametophytes. Heterospory is considered a significant evolutionary step towards the seed habit.

Key Examples & Features:

Psilopsida: — *Psilotum* (whisk ferns) - most primitive, dichotomous branching, no true leaves/roots.
Lycopsida: — *Lycopodium* (clubmoss), *Selaginella* (spike moss) - microphylls, strobili.
Sphenopsida: — *Equisetum* (horsetail) - jointed stems, whorled scale-like leaves, strobili.
Pteropsida: — *Dryopteris* (true ferns) - large macrophylls (fronds), sori with indusia.

Remember their 'amphibious' nature due to water-dependent fertilization, a critical point for NEET.

Prelims Revision Notes

Pteridophytes are the first terrestrial vascular plants, possessing true roots, stems, and leaves, along with xylem and phloem. This vascular tissue enables them to grow taller and colonize more diverse habitats than bryophytes.

Life Cycle & Alternation of Generations:

Dominant Generation: — Sporophyte ($2n$) – independent, photosynthetic, the main plant body.
Sporophyte produces: — Spores ($n$) via meiosis in sporangia.
Spores germinate into: — Gametophyte ($n$) – small, independent, photosynthetic prothallus.
Gametophyte produces: — Gametes ($n$) – antherozoids (male) from antheridia, egg (female) from archegonia.
Fertilization: — Fusion of gametes forms zygote ($2n$). Requires water for motile antherozoids.
Zygote develops into: — Embryo, then new sporophyte.

Spore Production:

Homosporous: — Produces one type of spore (e.g., *Lycopodium*, *Equisetum*, most ferns like *Dryopteris*). Spore $\rightarrow$ Bisexual gametophyte.
Heterosporous: — Produces two types of spores: microspores (smaller, $\rightarrow$ male gametophyte) and megaspores (larger, $\rightarrow$ female gametophyte). (e.g., *Selaginella*, *Salvinia*, *Marsilea*). This is a precursor to seed habit.

Classification (Four Classes with Examples):

1
Psilopsida: — *Psilotum* (Whisk fern) - Most primitive, dichotomous branching, no true leaves/roots.
2
Lycopsida: — *Lycopodium* (Clubmoss), *Selaginella* (Spike moss) - Microphylls, strobili.
3
Sphenopsida: — *Equisetum* (Horsetail) - Jointed stems, whorled scale-like leaves, strobili.
4
Pteropsida: — *Dryopteris*, *Adiantum* (True ferns) - Macrophylls (fronds), sori (clusters of sporangia), often covered by indusium.

Key Terms to Remember:

Sporophyll: — Leaf bearing sporangia.
Strobilus (Cone): — Compact structure of sporophylls.
Sori: — Clusters of sporangia on fern fronds.
Indusium: — Protective covering over sori.
Rhizome: — Underground stem.

NEET Focus: Understand the evolutionary significance of vascular tissue and heterospory. Be able to compare pteridophytes with bryophytes (non-vascular, dominant gametophyte) and gymnosperms (seed plants, no water for fertilization).

Vyyuha Quick Recall

Please Learn Some Pteridophyte Classifications:

Psilopsida (*Psilotum*)
Lycopsida (*Lycopodium*, *Selaginella*)
Sphenopsida (*Equisetum*)
Pteropsida (Ferns like *Dryopteris*)

To remember key features: Very Strong Growers With Heavy Spores

Vascular tissue
Sporophyte dominant
Gametophyte independent
Water for fertilization
Homospory/Heterospory
Spores for reproduction