How Are Plants Classified in the Plant Kingdom?
The plant kingdom is considered to play one of the most significant roles in the lives of mankind. Without the existence of plants, human survival would not be possible. It is an open book that plants are the essential source for the various vital components for the existence of life on the planet earth.
The most prominent component is oxygen, without which the life of most species would come towards extinction. This oxygen is released by the plants through the process of photosynthesis, where the green plants utilize the energy obtained from the sunlight that helps in converting carbon dioxide into oxygen. This oxygen that is available to humans is an essential source of breathing and survival.
Apart from this, the plant kingdom also gifts mankind with essential food and medicinal sources.
The plant kingdom is divided into two types: one is cryptogamia i.e plants without flowers and another one is phanerogamic plants with flower-like structures or flowers. In this way, Eichler classifies plant kingdoms into five divisions arranged in them in the order of evolution i.e Phylogeny. Cryptogamia is divided into three types, they are thallophyta, Bryophyta, Pteridophyta whereas Phanerogamic is divided into two types, they are Gymnosperm( flower-like structure) and Angiosperm(real flower).
Engler classifies plant kingdoms on the basis of embryos. They are thallophyta( embryo absent) and Embryophyta(embryo present). Further embryophyta is divided into two types based on fertilization one is Zooidogamy i.e male gametes are motile and reach the female gamete by swimming and another one is Siphonogama i.e male gamete is non-motile as male gamete reach the female gamete through pollen tube.
Classification of the Plant Kingdom in Order of Evolution
Division of Plant Kingdom
Cryptogamia (Plants without Flower): Those plants in which reproductive organs are not visible i.e not arranged in flower. A cryptogam is a name given to the plants that are known to reproduce via spores and without any involvement from the flowers or the seeds. The name Cryptogamae means “hidden reproduction” that hints at the process of reproductions without the seeds. These plants are also termed the non-seed bearing plants. Other titles such as the ‘thallophytes’, ‘lower plants’ and ‘spores plants’ are also devoted to this plant kingdom.
Thallophyta
Bryophyta
Pteridophyta
2. Phanerogamia (Plants with Flower-like Structure and Flower): Those plants in which reproductive organs are arranged in flower or flower-like structure. These plants are among the most vital divisions in the plant kingdom and consist of plants that have visible reproductive structures and organs, consisting of the angiosperms and the gymnosperms.
Gymnosperm (flower-like structure)
Angiosperm (Real flowers)
Classification of the Plant Kingdom on the Basis of Embryo
This Classification was given by Engler.
Thallophyta (Embryo Absent): This is a division of the plant kingdom encompassing primitive plant forms consisting of a simple plant body. They range from unicellular plants to larger ones such as the algae, fungi etc. they are known to be the polyphyletic group consisting of the non-mobile organisms. Other names used to describe them include “thalloid plants”, “lower plants”, “relatively simple plants” etc.
Embryophyta (Embryo Present): The Embryophyta, also known as the land plants, are said to comprise the maximum plant vegetation on the planet earth. One of the major innovations attributed to the land plants was the evolution of the embryo. The embryo is an immature sporophyte that is attached to or surrounded by the gametophyte. In most land plants that are seed-producing plants, the embryo remains dormant for a considerable period of time and is seen to undergo growth only if the required environmental conditions are met. They are further divided into two types on the basis of fertilization.
Zooidogamy: Fertilisation by zooidogamy i.e male gametes are motile and reach the female gametes by swimming. This phenomenon can be witnessed in plants such as algae, bryophytes, pteridophytes, and also in certain gymnosperms. They are further divided into two types:
a. Bryophyta
b. Pteridophyta
Siphonogamy: fertilization by Siphonogamy i.e male gamete is non-motile, male gamete reach the female gamete through pollen tube. This is the process wherein the pollen tubes in the plants are developed to transfer the male cells to the eggs. As a result of this, the spermatophytes are often termed siphonogama. They are further classified into three classes.
Gymnospermae
Monocotyledonae
Dicotyledonae: they are further divided into two different subclasses, they are Archichlamydeae (free petalous and non-petalous condition) and Monochlamydeae (united petalous condition).
Oswald Tippo Classification of Plant Kingdom
In 1942, Oswald Tippo classified the entire plant kingdom into two major divisions. This division was made on the basis of the presence or absence of the embryo in the plant. These were termed the Thallophyta and the Embryophyta.
It proposed the biggest phylogenetic classification of the plant kingdom and it is the most acceptable classification for books and study.
Thallophyta:
They are further divided into 10 types.
Cyanophyta: Blue-green algae
Euglenophyta: Euglenoids
Chlorophyta: Green algae
Chrysophyta: Yellow-green-algae
Pyrrophyta: Diatoms and Dinoflagellates
Phaeophyta: Brown algae
Rhodophyta: Red algae
Schizomycophyta: Bacteria
Myxomycophyta: Slime molds (false fungi)
Eumycophyta: True fungi
These ten divisions include three types of organisms, they are algae, bacteria and fungi.
B. Embryophyta:
They are further divided into two types on the basis of vascular tissue.
Atracheata: Bryophyta(non-vascular plants): they are further divided into three classes:
Hepaticopsida: Liverworts
Anthoceropsida: Hornworts
Bryopsida: Moss(true)
2. Tracheophyta (Vascular Plants): they are further divided into four classes.
a. Psilopsida: psilotum
b. Lycopsida: Club moss(false moss)
c. Sphenopsida: horsetail
d. Pteropsida: ferns, gymno, angiosperm
Karl Menz Classification of Plant Kingdom
He shows the importance of serology in taxonomy. Similarities and dissimilarities in the structure of protein help to know the phylogenetic relationship of living beings. Living organisms that are phylogenetically close relatives have more similarities in their proteins. Organisms that are distantly related have different proteins.
Haeckel Theory of Classification of Plant Kingdom
Haeckel gave the three kingdoms (Protista, Plantae, Animalia) a system of classification. He established the kingdom Protista. The term protista was given by C. Cuvier. He grouped those living organisms in Protista that did not have issues. Kingdom Protista includes Prokaryotes protozoa, Porifera, algae and fungi.
This classification was carried out to overcome the limitations and objections that had aroused from the Two kingdom plant classification. The inconsistencies that had come along with the two kingdom classification, were thought to be resolved with the introduction of a third kingdom, as a result of which, Protista was introduced as the third kingdom by Haeckel.
The arrangement of these kingdoms was carried out on the basis of the morphological complexity and the tissue system. The division of labour and the mode of nutrition also played a major role in the classification. The unicellular organisms, such as the algae and the fungi were separated from the other organisms as they lacked tissue differentiation. This new group called Protista, comprised organisms that lacked in the morphological complexities, division of labour, tissue system and the diverse modes of nutrients. This kingdom includes protozoa, bacteria, fungi and other organisms, although later the multicellular algae and fungi were removed from the group.
Copeland Classification System of Plant Kingdom
He gave the four kingdom systems of classification.
Mychota: Dougherty and Allen gave the name “Monera” to Mychota of Copeland. All prokaryotes are grouped in monera.
Protista or Prototista: Copeland grouped those eukaryotes in Protista, which are visually different from normal plants and animals.
Plants or Metaphyta: Remaining all eukaryotic plants are grouped.
Animalia and Metazoa: Remaining all eukaryotic animals are grouped.
R.H. Whittaker Classification of Plant Kingdom
He gave the five systems of classification. This classification was believed to be modern. This classification is based on three main characters:
Complexity of Cell: Cell is prokaryotic or eukaryotic, on the basis, kingdom Monera is formed. And all the prokaryotes are grouped into it.
Complexity of Organism: Organism is unicellular or multicellular, on the basis, kingdom Protista was formed and all the unicellular eukaryotes are grouped into it.
Nutrition: Organism is autotrophic and heterotrophic, on the basis kingdom mycota, Plantae and Animalia were formed. Except for fungi (heterotrophic) all the plants are autotrophs. Therefore fungi are separated from plants and placed in the kingdom mycota. And remaining all the autotrophic plants are placed in kingdom Plantae. Since all animals are heterotrophs, therefore they are placed in the fifth kingdom i.e kingdom Animalia.
Five Kingdom Classification
Monera: All the prokaryotes (Eubacteria, BGA, Mycoplasma) and Akaryotes(virus).
Protista: All the unicellular eukaryotes ( Dinoflagellates, Diatoms, Slime moulds and protozoa)
Mycota: True fungi
Plantae: All the multicellular plants- Algae, Bryophyta, Pteridophyta, Gymnosperm, Angiosperm.
Animalia: All multicellular animals.
FAQs on Plant Kingdom: Key Concepts & Classification
1. What are the five major divisions of the Plant Kingdom according to the NCERT syllabus?
The Plant Kingdom is broadly classified into five main divisions based on key characteristics like body differentiation, presence of vascular tissues, and seed formation. These divisions are:
- Algae: The simplest plants, typically aquatic, with a thallus-like body structure.
- Bryophytes: Non-vascular land plants that require water for reproduction, often called 'amphibians of the plant kingdom'.
- Pteridophytes: The first terrestrial plants to possess vascular tissues (xylem and phloem) but lack seeds.
- Gymnosperms: Plants that produce seeds which are not enclosed within a fruit (i.e., 'naked seeds').
- Angiosperms: Highly evolved flowering plants where seeds are enclosed within a fruit.
2. What are the main differences between the Plant Kingdom and the Animal Kingdom?
The primary differences between the Plant and Animal Kingdoms are based on nutrition, structure, and mobility. Key distinctions include:
- Nutrition: Plants are primarily autotrophic, producing their own food through photosynthesis using chlorophyll. Animals are heterotrophic, ingesting other organisms for energy.
- Cell Structure: Plant cells have a rigid cell wall made of cellulose and contain chloroplasts and a large central vacuole. Animal cells lack these structures.
- Mobility: Most plants are sessile (fixed in one place), while most animals are motile (capable of movement).
3. On what primary criteria is the Plant Kingdom classified?
The classification of the Plant Kingdom is based on a hierarchy of evolutionary features. The main criteria include:
- Plant Body: Whether the plant body is well-differentiated into true roots, stems, and leaves.
- Vascular System: The presence or absence of specialised vascular tissues like xylem and phloem for transporting water and nutrients.
- Seed Formation: Whether the plant produces seeds for reproduction.
- Seed Enclosure: If seeds are produced, whether they are naked (Gymnosperms) or enclosed within a fruit (Angiosperms).
4. What is the key difference between Bryophytes and Pteridophytes?
The main difference lies in their vascular system and dominant life cycle phase. Pteridophytes possess true vascular tissues (xylem and phloem), allowing them to grow taller and live in drier conditions. In contrast, Bryophytes lack these tissues. Additionally, the dominant phase in the life cycle of a bryophyte is the haploid gametophyte, while in a pteridophyte, it is the diploid sporophyte.
5. Why are bryophytes often called the 'amphibians of the plant kingdom'?
Bryophytes are called the 'amphibians of the plant kingdom' because while they are adapted to live on land, they are critically dependent on water for sexual reproduction. Their male gametes (antherozoids) are motile and need to swim through a film of water to reach and fertilise the female gamete (egg). This dual dependency on both terrestrial and aquatic environments is analogous to that of amphibians like frogs.
6. How do gymnosperms and angiosperms differ in their method of reproduction?
The primary reproductive difference is in the location of their ovules and the resulting seeds. In gymnosperms, the ovules are exposed on the surface of megasporophylls, leading to the formation of 'naked seeds' not enclosed in any specialised structure. In angiosperms, the ovules are safely enclosed within an ovary, which after fertilisation develops into a fruit that protects the seeds and aids in their dispersal.
7. What is 'alternation of generations' and why is this concept important in understanding plants?
Alternation of generations describes a plant's life cycle that alternates between two distinct, multicellular forms: a haploid gametophyte (which produces gametes) and a diploid sporophyte (which produces spores). This concept is crucial because it highlights the evolutionary trend in plants. In simpler plants like algae and bryophytes, the gametophyte is the dominant phase. In more advanced plants like pteridophytes, gymnosperms, and angiosperms, the sporophyte is the dominant phase, an adaptation that provides greater protection against harsh terrestrial conditions.
8. What evolutionary advantage did the development of vascular tissues provide to plants?
The development of vascular tissues, xylem and phloem, was a major evolutionary leap for plants. This innovation provided two key advantages:
- Efficient Transport: It allowed for the efficient transport of water and minerals from the soil to all parts of the plant, and the distribution of sugars from the leaves to where they are needed.
- Structural Support: The rigid nature of vascular tissues, particularly lignin in xylem, provided structural support, enabling plants to grow much taller, compete more effectively for sunlight, and colonise a wider range of terrestrial habitats.
9. Are all photosynthetic organisms classified under the Plant Kingdom? Explain briefly.
No, not all photosynthetic organisms belong to the Plant Kingdom. While photosynthesis is a key characteristic, classification also depends on other features like cellular structure and body organisation. For example, cyanobacteria (blue-green algae) are photosynthetic but are prokaryotes and belong to Kingdom Monera. Similarly, some photosynthetic organisms like diatoms and dinoflagellates are unicellular eukaryotes classified under Kingdom Protista.
