PLANT KINGDOM

Taxonomy (means, "arrangement law") is the science of classifying organisms in order to build universally agreed categorisation systems in which each creature is grouped into increasingly inclusive categories.

A hierarchical system refers to the grouping of bigger to smaller, more specialised categories. Carolus Linnaeus classified plants based on their vegetative characteristics or the androecium structure. Such systems were artificial Due to the fact that they were based on some morphological features, they differentiated closely related species. Furthermore, the artificial systems provided equal weightage to vegetative and sexual qualities; this is unacceptable because we know that vegetative features are frequently more easily modified by the environment.

In contrast, natural categorisation systems arose. which were based on natural affinities among species and took into account not only surface but also interior aspects such as ultrastructure, anatomy, embryology, and phytochemistry. George Bentham and Joseph Dalton Hooker proposed such a categorisation for flowering plants.

Phylogenetic System of Classification

The phylogenetic system of classification is based on evolutionary relation between various organisms. It was constructed with the help of cues from evolutionary links and ancestry and is used to depict the genetic links between creatures. It is represented by cladograms, which are groupings of organisms that include an ancestral species and its descendants.

This suggests that species from the same taxon have a common ancestor. We now use information from a variety of additional sources to assist us in resolving categorisation Issues. When there is no supporting fossil evidence, these become much more significant.

Numerical Taxonomy

Numerical taxonomy deals with the numerical grouping of taxonomic entities and is based on their characteristics. It seeks to construct a taxonomy via the use of numerical methods such as cluster analysis rather than a review of their characteristics.

Numerical Taxonomy is based on visible features and has bioinformatics programs dedicated to it. All characters are allocated numbers and codes, and the data is subsequently processed. Each character is given equal weightage in this manner, and hundreds of characters can be considered at the same time.

Cytotaxonomy

Cytotaxonomy is a discipline of taxonomy that classifies organisms based on their cellular structures. The chromosomal layout of an organism is most commonly used for this method. It is used to infer the connection between two organisms. The inference of species connections is based on the theory that closely related species have comparable chromosomal configurations called karyotypes. The similarities and differences in chromosomes are later used to reconstruct karyotype and species evolution.

Chemotaxonomy

Chemotaxonomy (or chemosystematics). is the taxonomic discipline that categorises and identifies organisms based on differences in their biochemical makeup. Plant selection based on chemotaxonomy is required for effective research of natural products. Taxonomists use chemical ingredients of plants to resolve confusion.

Classification of the Plant Kingdom

The plant kingdom is divided into subgroups. This classification is dependent on a few characteristics. namely:

(1) Plant body: The presence of a distinct plant body and parts such as root, stem, and leaves.

(2) Vascular system: The presence of a system for transportation in the plant body (a vascular system) such as xylem or phloem.

(3) Reproductive organs: Flowers and seeds, and whether the seeds are bare or wrapped in fruit, all contribute to seed production.

ALGAE

Division Thallophyta (means- Undifferentiated plants) are the simplest form of plants as they possess undifferentiated or thallus-like structures. The plant body cannot be differentiated into true roots, stems and leaves. Reproductive organs are single-celled non-jacketed structures called gametangia. Asexual reproduction occurs through spores. Currently, it includes only Algae.

Algae (sing: Alga-sea weed), are chlorophyll containing thallophytes creatures that are simple. autotrophic, and mostly aquatic. Only a few algae occur in moist terrestrial habitats like tree trunks, wet rocks, moist soil, etc.

Algae may be found symbiotically in the presence of fungus, such as in lichen. Algae, like other aquatic plants, are covered by a mucilage. Mucilage protects the algae from epiphyte growth and decaying effect of water. Algae vary greatly in appearance. Some examples are tabulated as follows:

Characteristics of Algae

The plant body is called a thallus, and it can be:

(1) Unicellular

(2) Colonial

(3) Filamentous

Vascular tissues are absent but mechanical tissues are present. Reproduction in algae is primarily vegetative. It may occur by fragmentation.

Asexual reproduction occurs by spore formation (zoospores). Zoospores are flagellated (motile) and on germination give a size to a new plant Sexual reproduction is also seen, sometimes by fusion of two gametes which can be:

(1) Isogamous: Male and female gamete have similar morphology. In Chlamydomonas, gametes can be flagellated and similar in size but in Spirogyra, gametes are similar and nonmotile in nature.

(2) Anisogamous: Male and female gametes have different morphology. In some species of Chlamydomonas, there is a fusion of two dissimilar gametes is seen.

(3) Oogamous: Male and female gametes have different morphology with female gamete significantly larger than male gamete. In Volvox and Fucus, fusion of one large, non-motile (female) gamete with smaller, motile (male) gamete.

Classification of Algae

Algae are divided in to three types basically:

(1) Chlorophyceae

(2) Phaeophyceae

(3) Rhodophyceae

Chlorophyceae (Green Algae)

Green algae can occur in all types of habitats. Only 10% of green algae are marine and majority of the species are freshwater.

Photosynthetic pigments are similar to higher plants chlorophyll a, chlorophyll b, carotenes and xanthophylls. Chloroplasts can be round, flat. filamentous, glass-shaped, spiral, or ribbon-shaped in several species.

Chloroplasts contain storage bodies called pyrenoids which store carbohydrates and protein. Some algae may be capable of storing food in the form of droplets of fat. Green algae frequently have a rigid cell wall made up of an internal lining comprising cellulose and an outer covering of pectose.

Vegetative reproduction is often accomplished by fragmentation. In asexual reproduction, different, spores like zoospores, aplanospores, hypnospores. akinetes, autospores, etc. are seen. Flagellated zoospores generated in zoosporangia are used for asexual reproduction. Sexual reproduction differs greatly and it can be isogamous, anisogamous, or oogamous.

Examples: Volvox, Ulothrix, Chlamydomonas, Spirogyra and Chara.

Phaeophyceae (Brown Algae)

Brown Algae comprises about 2000 species. The body consists of branched, filamentous forms (Ectocarpus) heavily branched forms (Kelps), and parenchymatous structures in higher forms (Fucus laminaria) They contain chlorophyll a and c, as well as carotenoids and xanthophylls. The quantity of fucoxanthin found in them determines their colour, which ranges from olive green to brown. Food is stored in the form of laminarin or mannitol (complex carbohydrates). The vegetative cells are covered by a cellulosic wall that is normally coated on the exterior by an algin gelatinous covering. The plant body is normally held to the surfaces using a holdfast and consists of Stalk, Stipe, and Frond (leaf-like photosynthetic organ).

Most brown algae reproduce asexually via biflagellate, pear-shaped zoospores and have two unequal laterally attached flagella. Isogamous, anisogamous, or oogamous sexual reproduction is also possible. Union of gametes can occur inside or outside the oogonium.

Examples: Ectocarpus, Sargassum Laminaria Dictyota and Fucus.

Rhodophyceae (Red Algae)

Red algae are defined as eukaryotic algae and have approx. 5000 living species. It is the most ancient group of algae. They are marine except for a few freshwater species (e.g. Batrachospermum). They contain pigments like chlorophyll a, d, and phycoerythrin. Cell wall is made up of cellulose, pectin and mucopolysaccharides called phycocolloids (e.g. agar, carrageenin, etc.). Food is stored in the form of floridean starch, structurally identical to amylopectin and glycogen.

Red algae often proliferate vegetatively by fragmentation. Asexual reproduction takes place variety of spores like neutral, monospores, tetraspores, carpospores and gammae. Sexual reproduction is oogamous. The male sex organ is called spermatangium or antheridium which produces a non-flagellated male gamete. The female sex organ is a flask-shaped structure called carpogonium. Examples: Polysiphonia, Porphyra, Gracilaria and Gelidium.

Economic Importance of Algae

(1) As Food: Some of the species of marine algae are used as food. Examples: Porphyra, Laminaria, Sargassum and Ulva.

(2) As Food Supplement: Green algae like Chlorella and blue-green algae like Spirulina are rich in proteins. They can be used as food supplements even by space travellers.

(3) For Photosynthesis: About 50% of carbon dioxide is fixed by algae in the world.

(4) Primary Producer: Algae are primary producers of food in large bodies of fresh. brackish and sea waters.

(5) Phycocolloid (Hydrocolloids): These are:

(i) Carrageenin from Chondrus is an emulsifier and clearing agent.

(ii) Agar from Gelidium and Gracilaria Is used as culture medium, canning fish and meat.

(iii) Algin from Laminaria, Fucus, and Sargassum is used in stabilising emulsions.

BRYOPHYTES

Bryophytes are also known as amphibians of plant kingdom as they need soil as well as water (sexual reproduction) to complete their life cycle. The plant body of bryophytes is more differentiated than algae.

Bryophytes include wide variety of mosses and liverworts found in wet, shaded areas.

Characteristics of Bryophytes

Bryophytes usually grow during the rainy season on damp soil, rocks, and walls. Vegetative reproduction occurs by fragmentation of tubers, gemmae, buds, and so on.

Gametophyte: Constitutes primary plant body, free living, haploid, produces gametes, roots are absent but there are rhizoids. Multicellular jacketed sex organs - antheridium (male sex organ) producing biflagellate antherozoids that fuse with flask-shaped archegonium (female sex organ) producing a zygote that does not immediately begin reduction division (meiosis).

Sporophyte: Multicellular body produced after fusion of gametes, not free-living, completely dependent on gametophyte for nutrition, some cells of the sporophyte undergo meiosis to produce haploid spores that germinate to produce gametophyte.

Classification of Bryophytes

Bryophytes can be divided into:

1) Liverworts

2) Mosses

Liverworts

Liverworts are often present in wet, shady habitats such as stream banks, marshy terrain, damp soil, tree barks, and deep woods. A liverwort's plant body (e.g. Marchantia) is a thalloid. The thallus is dorsoventrally placed due to which it adheres to the substrate tightly. The leafy members feature small leaf-like appendages on the stem-like structures in two rows.

Asexual reproduction in liverworts occurs through thalli fragmentation. It can also occur via formation of specialised structures known as gemmae. Gemmae are green, multicellular, asexual buds that grow in small receptacles on the thalli called gemma cups.

Caution:

Students usually get confused between gemmае and gemma cups. Gemmae and Gemma cups are only slightly different from each other. Gemma cups are cup-like structures that contain gemmae. The gemmае are tiny discs of haploid tissue that give birth to new gametophytes directly. Rainfall disperses them from gemma cups.

The gemmae separate from the parent body and germinate, resulting in the formation of new individuals. Male and female sex organs are produced on the same or different thalli during sexual reproduction. The sporophyte can be differentiated into foot. seta and capsule. Examples of liverworts are Riccia, Porella and Marchantia.

Mosses

The Life cycle of mosses is possibly the most important aspect of them. The most important stage of moss life cycle, Le, gametophyte stage consists of further two stages:

(1) The protonema stage is the first stage, which develops directly from a spore. It is a creeping stage that is green, branched, and usually filamentous.

(2) The second stage is the leafy stage, which develops as a lateral bud from the secondary protonema They are made up of upright, slender axes with spirally arranged leaves They are connected to the soil via rhizoids that are multicellular and branching. The sex organs are present in this stage.

Mosses reproduce vegetatively by fragmentation and budding in the secondary protonema. The sex organs, antheridia (male) and archegonia (female) are present at the top of the leafy branches during sexual reproduction. Zygote developed after fertilisation forms a sporophyte, consisting of a foot, seta and capsule. The capsule carries spores that are formed after meiosis. Mosses generally have a more elaborated mechanism of spore dispersal.

Examples of mosses are Funaria, Polytrichum and Sphagnum.

Economic Importance of Bryophytes:

(1) Sphagnum moss species provide peat, which has long been utilised as fuel Sphagnum may also be used as packing material for the shipment of living materials due to its ability to hold water.

(2) Mosses and lichens are also the first species to colonise rocks and thus old in ecological succession. They break down rocks, preparing the substrate for increased plant development.

(3) Mosses can also form a dense mat on upper layer of soil and reduces the impact of raln and prevent soil erosion.

PTERIDOPHYTES

Pteridophytes are the first terrestrial plant that has vascular tissue (xylem and phloem). They do not produce flowers or seeds; hence, they are frequently referred to as "cryptogams”.

They have sporophytic plant bodies inconspicuous gametophytes containing small sessile antheridia and partially embedded archegonia with a 4-rowed neck Vascular tissue develops for the first time in pteridophyte. They occur throughout the plant body.

Characteristics of Pteridophytes

(1) Meiospores are formed inside sporangia by sporic meiosis. The leaves bear sporangia are known as sporophylls.

(2) Spores may be similar (homosporous) as in most of the pteridophytes (E.g. Pteris and Adiantum). Some plants are heterosporous, i.e., with two types of spores, microspores and megaspores. Species that bear the heterospores are Marsilea, Salvinia and Selaginella.

(3) Sperms can be biflagellate or multiflagellated. They require an external water supply or water body to reach archegonia.

(4) Pteridophytes are generally present in damp, cool shady place Some of them can live in sandy soil Azolla, Salvinia and Marsilea are some examples of aquatic pteridophytes.

Pteridophytes are said to be the earliest plants to develop on land. It is thought that life started in the waters and gradually adapted to dry land over millions of years of development. They are cryptogams, without seeds, and are the first terrestrial plants to possess vascular tissues xylem and Phloem. Pteridophytes are seedless plants and reproduce by spores. They feature a distinct plant body that is divided into true root, stem, and leaves. The leaves are either small called microphylls (as in Selaginella) or large called macrophylls (as in ferns). The main plant body of pteridophytes is a sporophyte bearing sporangia subtended by leaf-like appendages called sporophylls. To safeguard the sensitive growth regions, the leaf tips curl inwards. In some cases, Like in Selaginella and Equisetum, sporophylls form distinct compact structures called strobili or cones. Spores are formed in spore mother cells by meiosis in sporangia.

Reproduction in pteridophytes is described as follows:

(1) The spores germinate and give rise to prothallus, which is tiny, free-living, primarily photosynthetic thalloid gametophytes.

(2) These gametophytes require cool wet, shaded conditions to thrive. Because of this very restricted need, as well as the necessity for water for fertilisation, the expansion of living pteridophytes is limited and geographically confined.

(3) Male and female sex organs, known as antheridia and archegonia, are found in gametophytes.

(4) Water is essential for the transmission of antherozoids-male gametes discharged by antheridia-to the archegonium's mouth.

(5) The zygote is formed when a male gamete fuses with an egg in the archegonium.

(6) After that, the zygote develops into a multicellular, well-differentiated sporophyte.

(7) When the spores of pteridophytes are of the same kind, the plants are known as homosporous whereas genera like Selaginella and Salvinia are heterosporous that produce two types of spores- macro (large) and micro (small).

(8) Megaspores and microspores both germinate. generating female and male gametophytes respectively.

(9) Female gametophytes are retained mostly on parent sporophytes for varied durations of time.

(10) Female gametophytes are the sites for transforming zygotes into young embryos. This event serves as a precursor to the seed pattern. which is regarded as a critical step in evolution.

Psilopsida (Psilophyta)

(1) They are the most primitive vascular pteridophytes.

(2) Roots are absent. Instead, rhizoids are present.

(3) Stem is dichotomously branched.

(4) It has two parts, aerial and rhizomatous. Aerial stems are green and photosynthetic.

(5) Leaves may be present or absent.

(6) Sporangia develop over the aerial stem either terminally or axially.

(7) Two primitive forms found in fossil state are Cooksonia and Rhynia. Living forms are known as living fossils.

Examples: Psilotum and Tmesipterus.

Lycopsida (Lycopods)

(1) Primitive vascular plants which have differentiated root, stem and leaves.

(2) Leaves are microphyllous; i.e., they do not produce a leaf gap in a vascular strand of the stem.

(3) Sporophylls form sporangiferous spikes or strobili.

(4) Sporangia develop either axially or adaxially.

(5) Branching Is dichotomous or pseudo dichotomous.

Examples: Lycopodium, Selaginella

Sphenopsida

(1) Also called "horsetails", these plants have photosynthesising. "segmented," hollow stems that are sometimes filled with pith.

(2) A whorl of leaves forms the junction between each section.

(3) Plants' subsurface sections are made up of jointed rhizomes from which roots and aerial axes arise.

(4) Intercalary meristems sprout in each segment of the stem and rhizome as the plant grows taller. In contrast, most seed plants develop from an apical meristem, which means that new growth originates solely from growing points (and widening of stems).

(5) Some horsetails have cones (strobili) at the terminals of their stems. These cones are made up of spirally organised sporangiophores with sporangia on their edges.

Example: Equisetum.

Pteropsida

(1) The Pteropsida are the most developed group of lower vascular plants. Ferns are the most extensively spread pteridophytes.

(2) The subterranean rhizomatous stem of the sporophyte can be elongated or tuberous. In certain circumstances, the rhizome is coated with hairs known as ramenta.

(3) The leaves are aerial and megaphyllous, while the remainder of the plant Is underground. Roots, like those of other pteridophytes, are always adventitious.

Examples: Adiantum, Pteris and Dryopteris.

Economic Importance of Pteridophytes

(1) Food: Like other plants, pteridophytes contain a decent source of food for animals. Sporocarps of Marsilea, a water fern, yield starch that is cooked and consumed by some tribes.

(2) Soil Binding: By their growth, Pteridophytes bind the soil even along hill slopes. They protect soil from soil erosion.

(3) Scouring: Equisetum stems have been used in scouring (utensils cleaning) and polishing of metals. Equisetum species are also known as scouring rushes.

(4) Nitrogen Fixation: A water fern named Azolla has a symbiotic association with cyanobacteria which carry out nitrogen fixation. E.g. Anabaena azollae used to be inoculated in the paddy fields to work as biofertilizers.

(5) Medicines: An anthelmintic drug is obtained from rhizome of Dryopteris.

(6) Ornamental: Ferns are grown as ornamental plants for their delicate and graceful leaves.

PHANEROGAMAE

GYMNOSPERMS

Phanerogamae are plants that bear seeds thus, also known as seed-bearing plants. These plants have visual sex organs and also known as spermatophytes. They are the most advanced plants possessing true roots, leaves, stems and well-developed vascular bundles. There are two types of phanerogams named as Gymnosperms and Angiosperms.

Pinus, Cedrus and Cycas are examples of gymnosperms and these are found in gardens of homes, parks and hotels as ornamental plants.

Gymnosperms are the plants in which the ovules are not enclosed by the ovary wall and thus, remain exposed and naked both pre and post-fertilisation. Developing seeds are naked. It includes a variety of trees of all sizes from shrubs to medium -sized trees or tall trees.

Important

The giant redwood tree Sequoia is one of the tallest tree species.

Plant Body of Gymnosperms

Root system

Generally, tap root system is found, fungal association in the form of mycorrhiza can be seen in Pinus, and specialised roots called coralloid roots are found in Cycas which are associated with nitrogen-fixing cyanobacteria that help to fix atmospheric nitrogen into the soil.

Stem

The stems may be unbranched (Cycas) or branched (Pinus and Cedrus).

Leaves

Leaves may be simple or compound leaves. The pinnate leaves of Cycas can last for several years. Gymnosperm leaves are well-adapted to hold out against the extremes of temperature, humidity, and wind. Their needle-like leaves reduce surface area, as well as their thick cuticle and sunken stomata helps to reduce transpiration (water loss) rate.

Reproduction in Gymnosperms

They produce two types of spores, Le. haploid microspores and megaspores (both are haploid in nature). therefore known as heterosporous. Spores are produced in sporangia that are present on sporophylls. Sporophylls are spirally arranged along an axis to form compact strobili or cones.

Strobili which bear microsporophylls and microsporangia are known as male strobili or microsporangiate. Microspores develop into the male gametophyte (highly reduced), known as pollen grains, their development takes place inside the microsporangia.

Strobili that bears megasporophylls or megasporangia is known as megasporangiate or the female strobili. Megaspore mother cell (MMC) is differentiated from one of the cells of nucellus, it is protected by envelopes and forms a composite structure called an ovule. Ovules are found on megasporophylls which are aggregated to form the female strobili or cone. MMC undergoes meiotic division to produce four megaspores enclosed within the megasporangium. One of the megaspores enclosed within the megasporangium, develops into multicellular female gametophyte, it possesses two or more archegonia or female sex organs. This multicellular female gametophyte is retained within the megasporangium.

Important

The male or female cones or strobili may be borne on the same tree (Pinus). However, in Cycas male cones and megasporophylls are borne on different trees.

In male and female gametophytes, they do not have an independent free-living existence in this environment, instead, it remains within the sporangia and is retained on sporophyte. Pollen grains are released from the microsporangium, carried by the wind, and come into contact with the opening of the ovule produced on megasporophylls. Pollen tube is developed, which grows towards archegonia in the ovules it carries the male gametes near the archegonia's opening where fertilisation occurs, zygote is formed, zygote develops into an embryo, and ovules mature into seeds. Seeds can be either bare or uncovered.

Economic Importance of Gymnosperms

Gymnosperms are economically very significant. Conifers are employed in paper. furniture, and lumbering industries. White spruce is used in the music industry to make instruments like violins. For example, Ginkgo, Pinus, Cycas, and some others are used as a good sources of food. They are also commonly utilised in the pharmaceutical industries to make a variety of drugs to treat infectious diseases and allergies such as cold, cough, asthma, and bronchitis. They are also utilised as ornamental plants and trees and are planted in gardens, parks, and other locations because of their beautiful leaves.

ANGIOSPERMS

Unlike the gymnosperms where the ovules are naked, in the angiosperms or flowering plants, the pollen grains and ovules are developed in specialised structures called flowers. In angiosperms, the seeds are enclosed in fruits. The angiosperms are an exceptionally large group of plants occurring in wide range of habitats. They range in size from the smallest Wolffia to tall trees of Eucalyptus (over 100 metres). They provide us with food, fodder, fuel, medicines and several other commercially important products. They are divided into two classes: the dicotyledons and the monocotyledons.

DOWNLAOD THE ASSIGNMENT HERE:

FOLLOW THE INSTRUCTIONS FOR DOWNLOAD THIS ASSIGNMENT:

1. SEARCH WWW.SCIENCEARENA.IN

2. OPEN EDUCATION AND RESOURCES IN MENU BAR.

3. SINGLE CLICK DOWNLOAD AVAILABLE IN DOWNLAOD SECTION.

https://www.sciencearena.in/p/education-resources.html

DOWNLAOD THE ASSIGNMENT HERE:

https://www.sciencearena.in/p/education-resources.html

11TH CLASS NOTES:

THE LIVING WORLD:

https://www.sciencearena.in/2025/08/the-living-world.html

BIOLOGICAL CLASSIFICATION: