INTRODUCTION:
CLASSIFICATION:
They can be classified into various groups based on the presence or absence of flowers. The plant kingdom is mainly divided into two types-A. Cryptogamia
B. Phanerogamia
A. Cryptogamia :
Cryptogams refer to plants that do not produce flowers or seeds for reproduction and reproduce by means of spores instead of seeds. It included non flowering plants or those without visible reproductive structures. It includes three sub groups:
1. Thallophyta : Thallophyta refers to a group of plants characterized by a thallus-like body organization.
Thallus refers to a plant body that is not differentiated into true roots, stems, and leaves. It is a flat, undifferentiated structure.
Again, Its divided into two groups -
- Algae : It is a photosynthetic organism that can be found in diverse habitats, including aquatic environments (freshwater and marine) and moist terrestrial habitats. They can have a wide range of thallus structures and can be classified into different divisions based on their pigmentation and other characteristics.
Divisions of algae :
- Chlorophyta (green algae): Examples include Spirogyra and Ulva.
- Rhodophyta (red algae): Examples include Polysiphonia and Porphyra.
- Phaeophyta (brown algae): Examples include Fucus and Sargassum.
- Fungi : Fungi are eukaryotic organisms that obtain nutrients through absorption. They do not have chlorophyll and cannot perform photosynthesis. Fungi can have a variety of thallus structures, including multicellular filamentous forms (hyphae) or unicellular forms (yeasts).
Some common groups of fungi include:
- Zygomycota : Examples include Rhizopus and Mucor.
- Ascomycota : Examples include Saccharomyces (yeast) and Penicillium.
- Basidiomycota : Examples include Agaricus (mushrooms) and Ustilago (smut fungi).
However, this classification is no longer considered valid because these groups are now classified separately based on their evolutionary relationships and distinct characteristics.
Age-Precambrian to recent.
2. Bryophytes: This group includes non-vascular plants such as mosses. They reproduce through spores and lack true roots, stems, and leaves.
Age-Precambrian to recent
3. Pteridophyta: Pteridophyta refers to a division of vascular plants that includes ferns and horsetails. Unlike bryophytes, pteridophytes have specialized vascular tissues for the transport of water and nutrients.
They reproduce through spores and have a dominant sporophyte generation in their life cycle ( the first group to evolve true vascular tissues.)
B. Phanerogamia:
"Phanerogamia" is an older term that was used to refer to plants that produce visible reproductive structures, such as flowers and seeds. It is not commonly used in modern plant taxonomy. It has two main types
1. Gymnosperm
2. Angiosperm
1. Gymnosperm : Gymnosperms are a group of seed-producing plants that do not have enclosed or protected seeds. The word "gymnosperm" originates from the Greek terms "gymnos," which means "naked," and "sperma," meaning "seed". This name refers to the fact that the seeds are not enclosed in a fruit but are instead exposed or "naked" on the surface of specialized structures called cones or strobili.
Gymnosperms are a diverse group of plants that have been around for hundreds of millions of years and were dominant during the Mesozoic Era, commonly known as the age of dinosaurs. They include several well-known plant families such as conifers (e.g., pines, spruces, firs), cycads, Ginkgo biloba, and Gnetophytes.
Characteristics of gymnosperms :
a. Naked seeds : As mentioned earlier, gymnosperms have seeds that are not enclosed in fruits. The seeds are usually borne on the scales of cones or in modified cone-like structures.
b. Cones or strobili : Gymnosperms produce reproductive structures called cones or strobili. These structures can be male or female and they bear the reproductive organs of the plant. Male cones produce pollen. Female cones contain ovules, which turn into seeds after fertilization.
c. Evergreen habit : Most gymnosperms are evergreen, meaning they retain their leaves (usually needle-like or scale-like) throughout the year. This adaptation allows them to survive in cold or dry environments.
d. Adaptation to harsh conditions : Gymnosperms are well-adapted to diverse environments including cold climates, high altitudes and nutrient poor soils. Their needle-like leaves and thick waxy cuticles help reduce water loss and protect against freezing temperatures.
e. Heterospory : Gymnosperms exhibit heterospory, means they produce two types of spores : microspores and megaspores.
Microspores give rise to male gametophytes (pollen grains), while megaspores develop into female gametophytes within the ovules.
2.Angiosperm : It also known as flowering plants and the largest group of plants in the plant kingdom. They are characterized by the production of flowers, which contain reproductive structures called ovaries that develop into fruits, enclosing and protecting seeds. Angiosperms are extremely diverse and can be found in a various habitats across the globe.
Angiosperms, can be further classified into two major classes :
1. Dicotyledons (Magnoliopsida): Dicots are angiosperms characterized by having two cotyledons (seed leaves) in their embryo. They have branching veins in their leaves, floral parts usually in multiples of four or five, and a taproot system. Examples of dicotyledons include roses, sunflowers, beans, and oak trees.
2.Monocotyledons (Liliopsida): Monocots are angiosperms characterized by having a single cotyledon in their embryo. They have parallel veins in their leaves, floral parts usually in multiples of three, and a fibrous root system. Examples of monocotyledons include grasses, lilies, orchids and palms.
CONCLUSION :
The plant kingdom is classified into major groups based on common traits and evolutionary history. These include bryophytes (like mosses), pteridophytes (ferns), gymnosperms (such as conifers) and angiosperms (flowering plants). Each group has unique features and adaptations that reflect their growth, reproduction and survival strategies across different environments.
The classification of the plant kingdom is an ongoing process, with new discoveries and research leading to revisions and refinements.
Plant classification helps us understand their diversity, uses and ecological roles. It reveals evolutionary relationships and supports the conservation and sustainable use of plant resources.
