pteridophytes.pptx-1
PTERIDOPHYTES
Lecturer: Dr. S. Koba-Dunge
Course: BI0111F
Course Outline
General Characteristics of Pteridophytes
Classification of Pteridophytes
Morphology of Pteridophytes
Evolution of Pteridophytes
Life Cycles
Economic, ecological and medicinal importance of bryophytes
Introduction to Pteridophytes
Definition:
Pteridophytes are seedless vascular plants that reproduce by spores rather than seeds.
Vascular Tissue:
Considered the first plants to evolve true vascular tissues (xylem and phloem).
Habitat:
Commonly found in moist, shady environments, as water is required for fertilization.
Examples:
Common examples include ferns.
General Characteristics of Pteridophytes
Vascular Structure:
They are vascular plants containing xylem and phloem.
Reproductive Features:
Do not produce seeds, flowers, or fruits.
Reproduce using spores.
Dominance of Sporophyte Generation:
The sporophyte generation is dominant and independent.
The gametophyte (prothallus) is small and usually independent.
Fertilization Requirement:
Requires water because sperm must swim to the egg.
Structural Components:
Possess true roots, stems, and leaves.
Habitat Preference:
Mostly grow in moist and shady habitats.
Classification of Pteridophytes
Historical Perspective:
The classification of pteridophytes has undergone various changes over the years.
Traditionally based on the presence or absence of seeds.
Vascular plants with seeds are classified under Spermatophyta and those without seeds under Pteridophyta.
Main Classes:
Traditionally, they are divided into four main classes:
Class 1: Psilopsida (Whisk Ferns)
Characteristics:
Considered the most primitive pteridophytes.
Lack true roots (have rhizoids instead).
Have simple, dichotomously branched stems.
Leaves are very small or absent.
Sporangia are fused to form synangia.
Example:
Psilotum
Habitat:
Mostly found in tropical and subtropical regions, often growing on rocks or as epiphytes.
Class 2: Lycopsida (Club Mosses)
Characteristics:
Small herbaceous plants.
Leaves are microphylls (small leaves with a single vein).
Stems may be creeping or upright.
Sporangia are borne on specialized leaves called sporophylls.
Sporophylls form strobili (cones).
Examples:
Lycopodium and Selaginella
Class 3: Sphenopsida (Horsetails)
Characteristics:
Hollow and jointed stems.
Leaves are small and arranged in whorls around the nodes.
Stems contain silica, making them rough.
Sporangia occur in strobili at the tips of stems.
Example:
Equisetum
Class 4: Pteropsida (True Ferns)
Characteristics:
Largest and most diverse group of pteridophytes.
Large leaves called fronds.
Leaves usually show circinate vernation (young leaves are coiled).
Sporangia occur in clusters called sori on the underside of leaves.
Well-developed roots, stems, and leaves.
Examples:
Pteridium, Adiantum, and Nephrolepis
Summary of Classification of Pteridophytes
Class | Common Name | Key Features | Example |
|---|---|---|---|
Psilopsida | Whisk ferns | No true roots, simple stems | Psilotum |
Lycopsida | Club mosses | Microphyll leaves, strobili | Lycopodium |
Sphenopsida | Horsetails | Jointed stems, silica deposits | Equisetum |
Pteropsida | True ferns | Large fronds, sori on leaves | Pteridium |
Classification by Historical Figures
Smith (1955), Bold (1957), and Zimmerman (1959):
Psilophyta: Most primitive with rootless rhizoids and dichotomously branched stems.
Lycophyta: Microphyllous leaves, sporophylls aggregate to form strobili or cones.
Examples: Selaginella, Lycopodium
Sphenophyta (Horsetail): Differentiated plant body, scaly leaves around nodes, sporangia form strobili.
Example: Equisetum
Pterophyta: Differentiated plant body with fronds showing circinate vernation and sori on leaves.
Example: Pteris
Morphology of Pteridophytes
The morphology mainly describes the structure of the sporophyte plant body, the dominant and visible stage in their life cycle.
General Morphological Characteristics:
Plant body is well differentiated into roots, stems, and leaves.
Contains vascular tissues (xylem and phloem).
Sporophyte is the dominant generation.
Reproduction occurs by spores produced in sporangia.
Leaves may be microphylls or megaphylls.
Most species grow in moist and shady environments.
Root System
Pteridophytes possess true roots that develop from the stem.
Functions:
Anchoring the plant in the soil.
Stem
Types of Stems:
Rhizome:
An underground horizontal stem that produces roots and leaves from nodes.
Aerial Stem:
An upright stem growing above ground, providing support to leaves.
Leaves
Roles:
Important for photosynthesis and reproduction.
Generally called fronds in ferns.
Types of Leaves:
Microphylls:
Small leaves.
Megaphylls:
Large leaves with complex branching veins.
Evolution of Pteridophytes
Pteridophytes are believed to have evolved from early primitive land plants during the Paleozoic era, particularly in the Silurian and Devonian periods.
Characteristics of Early Plants:
Dichotomously branching stems.
No true leaves or roots.
Simple sporangia.
These early plants are often referred to as Rhyniophytes, which are considered ancestors of many vascular plants.
Major Evolutionary Advances in Pteridophytes
Development of Vascular Tissue:
Allowed efficient transport of water and nutrients.
Development of True Organs:
Unlike bryophytes, pteridophytes developed true plant organs: roots, stems, and leaves, improving anchorage, nutrient absorption, and photosynthesis.
Dominant Sporophyte Generation:
In bryophytes, the gametophyte is dominant, whereas in pteridophytes, the sporophyte became the dominant generation.
Evolution of Leaves:
Leaves evolved gradually in pteridophytes.
Evolution of Reproductive Structures:
Reproduce using spores produced in sporangia.
Two evolutionary types of spores:
Homospory: Only one type of spore.
Heterospory: Produces two different spores.
Life Cycle and Reproduction of Pteridophytes
Pteridophytes reproduce mainly by spores and exhibit a life cycle characterized by alternation of generations.
Stages in Life Cycle:
Sporophyte (diploid – 2n)
Gametophyte (haploid – n)
The sporophyte generation is dominant and independent, while the gametophyte is smaller and usually short-lived.
Examples of Pteridophytes:
Pteridium
Vegetative Reproduction
Pteridophytes can reproduce vegetatively in addition to spores.
Methods of Vegetative Reproduction:
Fragmentation:
Parts of the plant break off and grow into new plants.
Rhizome Growth:
Horizontal growth of underground stems (rhizomes) that produce new shoots and roots.
Example: Pteridium
Spore Formation (Asexual Reproduction)
Pteridophytes reproduce asexually by producing spores in structures called sporangia.
Characteristics of Sporangia:
Small, sac-like structures that produce spores by meiosis.
In ferns, sporangia are usually grouped into clusters called sori on the underside of leaves.
Example: Pteridium
Life Cycle in Pteridophytes
Life cycle alternates between two generations:
A diploid sporophyte (2n)
A haploid gametophyte (n)
1. Sporophytic Generation
The sporophyte is the free-living, multicellular, diploid dominant phase.
Features:
Has a well-differentiated plant body and produces haploid spores by meiosis, which germinate to form gametophytes.
Can be homosporous or heterosporous.
2. Gametophytic Generation
The gametophyte is a haploid, free-living, mostly photosynthetic, multicellular thalloid structure known as a prothallus.
Requirements:
Requires cool, shady, and damp places to grow and the presence of water for fertilization.
Reproduction:
Bears the sex organs that give rise to haploid gametes by mitosis.
Types of Gametophytes:
Unisexual: Male and female sex organs are borne on different gametophytic thalli.
Bisexual: Male and female sex organs are borne on the same thalli, mostly seen in homosporous pteridophytes.
Life Cycle of Pteridophytes is described as haplo-diplontic
Exhibits equal prevalence of the alternating haploid gametophyte and diploid sporophyte generations.
A multicellular diploid (2n) phase → sporophyte (dominant and independent)
A multicellular haploid (n) phase → gametophyte (smaller, short-lived).
The cycle alternates between these via meiosis (reduces chromosome number) and fusion/syngamy.
Detailed Life Cycle in Pteridophytes
Sporophyte (2n):
This is the dominant, visible plant (e.g., the leafy fern-like body).
It is diploid (2n).
Through mitosis, it grows and develops reproductive structures (sporangia).
Meiosis:
Occurs inside special sporangia on the sporophyte, producing haploid (n) spores from diploid cells.
Microspore (n) → Male Gametophyte (n):
The microspore germinates via mitosis, developing into a reduced male gametophyte (microgametophyte) that produces male gametes (sperm, n).
Megaspor (n) → Female Gametophyte (n):
The megaspore germinates via mitosis and develops into a female gametophyte (megagametophyte), which produces female gametes (eggs, n), usually in archegonia.
Fusion of Male Gamete and Female Gamete:
Fertilization occurs when sperm swims to the egg (requires water).
Fusion (syngamy) forms a diploid zygote (2n).
**Zygote (2n