Kingdom Plantae – Class 11 Biology

In earlier systems of classification, only habit or external morphological characters were considered the sole basis of classification. But later on, organisms were classified on the basis of their natural affinities and finally on the basis of phylogeny (evolutionary tendencies). The living organisms from the beginning have been grouped into different groups/kingdoms to classify them. 

Two Kingdom System: Linnaeus (1758) in the 18th century proposed a two-kingdom system of classification and divided all organisms into two kingdoms viz. Plantae and Animalia on the basis of some structural and functional characteristics like locomotion, response to stimuli; mode of nutrition and cell wall. The animal kingdom contains motile heterotrophic organisms. In the plant kingdom, static/fixed organisms which fed autotrophically by photosynthesis were kept. Microorganisms were included in both kingdoms. 

Five Kingdom System: It was developed by American taxonomist Robert H. Whittaker (1969). It is a phylogenetic system based on three main criteria:

1. The complexity of cell structure (prokaryotes and eukaryotes).
2. The complexity of organisms, i.e., thallus organisation (unicellular or multicellular organism).
3. Mode of nutrition autotrophic (holophytic) or heterotrophic [absorptive (saprozoic or parasitic) or ingestive (holozoic)]. The mode of nutrition is a major criterion of classification in this system. Two other criteria used in this system are:
4. The ecological role of organisms was also considered as one of the criteria and accordingly, organisms were called producers, consumers and decomposers.
5. Phylogenetic relationship showing the direction of evolution.

The five kingdoms are Monera – Protista – Plantae, Mycota (Fungi) – Animalia.

Kingdom Plantae

Characteristics of Kingdom Plantae

• Plantae includes multicellular organisms except for some earliest relatives of algae.
• They are eukaryotes, i.e., a eukaryotic cell has a nucleus and membrane-bound cellular organelles.
• Cellulose-containing cell wall occurs around the cell.
• A mature plant commonly maintains a single large central vacuole bound by a tonoplast (membrane).
• Starch and lipids (oil/fat) is the reserve food of plants.
• In all plants, cells occur double membrane-covered cell organelles, called plastids. Some plastids possess photosynthetic pigments (chlorophylls). They are called chloroplasts.
• Autotrophic nutrition, in which plants make their own food with the help of photosynthesis.
• Indefinite growth in plants is mainly because of the presence of growing points.
• The irregular body form of the plants is due to the presence of branches.

Classification of Kingdom Plantae

Classification of Kingdom Plantae

Kingdom Plantae is further divided into several divisions based on several criteria. Foremost first classification among plants depends on the well-differentiated plant body or different components. The next level of classification is based on whether the differentiated plant body has special tissues (vascular tissues-the xylem and phloem) for the transport of water and other substances within the plant body. Depending on many criteria, the plant kingdom is classified into divisions described below:

Algae

• Most primitive and simple plants. The plant body does not evolve into a stem, root and leaves, but it is in the form of a complete thallus.
• Most algae are aquatic, (both marine and freshwater); some are terrestrial, that is, live on land near moist places.
• They are autotrophic, i.e., synthesise their own food. 
• Asexual reproduction generally takes place by spores.
• Example: Green algae – Ulothrix, Cladophora, Spirogyra, Ulva and Chara; Red algae – Batra, Polysiphonia; Brown algae (Laminaria, Fucus, Sargassum).

Classification of Algae

The algae are classified (into three groups i.e. Red, Brown and Green algae, according to the five-kingdom system) on the basis of pigment colour, nature of stored food material and cell organisation.

Red Algae – Rhodophyta

• They are an ancient group of algae.
• They are marine except for a few freshwater species (e.g., Batrachospermum or frog spawn alga).
• Red algae are autotrophic with the exception of a few like Harveyella which are colourless and parasitic on other red algae.
• A motile stage is absent.
• The body form varies from unicellular (e.g., Porphyridium), filamentous (e.g., Asterocystis and Spermathamnion), parenchymatous sheets (e.g., Porphyra), ribbons (e.g., Chondrus) to lace-like seaweeds (e.g., Gelidium and Gracilaria).
• They are seldom very large. The size varies from microscopic forms to about half a metre.
• The cell wall possesses cellulose, pectic compounds and mucopolysaccharides called phycocolloids (usually sulphated). The important phycocolloids of rhodophytes are agar, carrageenan and funori.
• Some of them have a layer of calcium carbonate over their walls.
•  The photosynthetic organelles are called chromatophores. They have single thylakoids.
• Photosynthetic pigments are chlorophyll a, carotenoids and phycobilins. Chlorophyll d is seen in some cases. Phycobilins are water-soluble pigments of two types, red-coloured phycoerythrin and blue-coloured phycocyanin and allophycocyanin.
• The red colour is due to phycoerythrin. It is able to absorb blue-green light. The red algae living in shallower waters do not appear reddish due to the lesser synthesis of phycoerythrin. They are greenish, violet or purplish e.g., species of Batrachospermum found in shallow water.
• Vegetative reproduction takes place through fragmentation and regeneration of holdfast.
• Asexual reproduction occurs through a variety of spores- neutral spores, monospores, tetraspores, and carpospores.
• Sexual reproduction is specialized. 

Economic Importance

• Food: A number of red algae are edible, e.g. Porphyra, Chondrus (Irish Moss); Rhodymenia (also called sheep’s weed) is used as fodder.
• Phycocolloids: Agar is used in solidifying laboratory culture media and is added as a thickener in the preparation of jellies, puddings, cheese, bakery, etc. It is obtained from Gelidium and Gracilaria. Carrageenan is used as a clearing agent in liquors, and leather finishing and as an emulsifier in chocolates, ie-creams, toothpaste, etc. It is extracted from Chondrus. Funori is a glue used as an adhesive. It is got from Gloiopeltis.
• Bromine: It is obtained from Rhodomela
• Medicines: Corallina cures worm infections. Polysiphonia has antibacterial properties. Agar is a laxative. Carrageenan can coagulate blood.

Brown Algae – Phaeophyta

• Except for a few freshwater forms, all are marine. They occur in both tidal and subtidal regions of colder seas.
• Unicellular forms are absent. The body branched filamentous structure in lower forms (e.g., Ectocarpus) and parenchymatous structure in higher forms (e.g., Laminaria, Macrocystis).
• They include the largest algae. The giant brown algae are called kelps. The largest kelps are Macrocystis (40-60m) and Nereocystis (20-30m).
• The body is generally differentiated into holdfast, stipe and lamina or frond, which is a leaf-like photosynthetic organ.
• The large forms have air vesicles or bladders for buoyancy.
• Lamina of brown algae may be simple or divided variously. Despite its size and complexity, the lamina of kelp is annual.
• Chromatophores possess 3-thylakoid lamellae.
• Photosynthetic pigments are chlorophyll a, chlorophyll c and carotenoids (carotenes and xanthophylls). The brown colour is due to xanthophyll called fucoxanthin.
• Food reserve is laminarin or mannitol (both carbohydrates) and lipids.
• Cells possess refractile vesicles called fucoidan vesicles which have a phenolic chemical named fucosan.
• Conducting tubes or trumpet hyphae are seen in the kelps. The tubes possess sieva septa They take part in the conduction of food materials.
• Asexual reproduction occurs with the help of both motile and nonmotile spores (e.g., neutral spores, tetraspores, monospores). The motile spores or zoospores have heterokont flagellation with one smooth flagellum and the other of tinsel type.
• Sexual reproduction varies from isogamy, anisogamy to oogamy. Fucus shows oogamy.

Economic Importance

• Food: e.g., Laminaria (Devil’s apron), Alaria, Macrocystis, Sargassum.
• Fouling of ships: Some get attached to hulls of ships, e.g., Ectocarpus.
• lodine: Fucus, Laminaria and Kelps are rich sources of iodine. Macrocystis and Nereocystis are rich sources of potash.
• Medicines: Sodium laminarin sulphate is a blood anticoagulant. 
• Alginic Acid: It is phycocolloid, obtained from many brown algae (e.g., Laminaria, Macrocystis, Nereocystis, Fucus, Sargassum). Alginic acid and its salts are used in obtaining emulsions (ice creams, toothpaste, ointments, creams, cosmetics, shampoos, etc), flame-proof plastics, security glass, surgical threads and coating of medicinal pills.

Green Algae – Chlorophyta

• They occur in all habitats. Only ten per cent are marine. The majority are fresh water. Many are sub-aerial. They grow on moist soils, walls, rocks and tree trunks.
• They may be epiphytic, endophytic, epizoic or endozoic. Zoochlorella is associated with sponges. Characium occurs on crustaceans, Cladophora on molluscan shells, while Trichophilus occurs on sloths (a mammal). Some are constituents of lichens. It reduces the yield of tea (red rust of tea), coffee, pepper and Citrus fruits.
• The thallus is of different types – unicellular flagellate (e.g., Chlamydomonas), unicellular non-flagellate (e.g., Chlorella Acetabularia or umbrella plant which is several centimetres in length and is differentiated into uninucleate holdfast, an elongated stalk and umbrella-like cap), flagellate colonies (e.g., Volvox), nonflagellate colonies i.e., the thallus is not divided by septa (e.g., Scenedesmus), coenocytic and siphonaceous (e.g., Caulerpa) heterotrichous (with prostrate and vertical branches, e.g., Drapamaldia), and parenchymatous (e.g., Ulva). The colony of volvox is called coenobium. The number of cells in this colony can be as low as 500 and as high as 60,000. The alga rotates during swimming. It is, therefore, also called rolling alga. Chara or aquatic horsetail or stonewort is fixed to the substratum by means of rhizoids.
• The cell wall contains cellulose with a few exceptions. Cellulose forms an inner layer and there is an outer layer of pectose.
• Chloroplasts have 2-20 thylakoid lamellae. Chloroplasts have pyrenoids for the storage of starch. Pyrenoids contain protein besides starch. In flagellate forms, an eyespot occurs in the chloroplasts.
• A reserved form of food is starch.
• Asexual reproduction occurs by both mitospores and meiospores. The asexual spores are zoospores, aplanospores, hypnospores, akinetes, autospores, etc. Autospores (e.g.. Chlorella) are quite similar to parents but are comparatively smaller in size.
• Volvox shows oogamy.
• Three types of life cycle occur – haplontic, diplontic and diplohaplontic.

Economic Importance

• Antibiotics: These are extracted from Chlorella and Caulerpa.
• Cephaleuros: It reduces the yield of tea, coffee, pepper, citrus, etc.
• Sewage Oxidation: Sewage oxidation ponds contain green algae, e.g., Chlamydomonas, and Chlorella.

Bryophyta

• Bryophytes are small multicellular green land plants. These simple land plants are limited to shady damp places. They are also known as amphibians of the plant kingdom.
• Their plant body is a flat, green thallus in liverworts (Riccia, Marchantia) and leafy, erect structures in mosses (Funaria, Sphagnum). They lack real roots, stems and leaves and have no flowers.
• A true vascular system is absent in bryophytes.
• The sex organs are multicellular.
• An embryo is formed upon fertilisation.
• Examples: Riccia, Marchantia, Anthoceros, Funaria, Barbula.
• The dominant phase is a free-living gametophyte.
• They show heteromorphic alternation of generation.

Liverworts	Mosses
The leaves are without a midrib.	The leaves generally have a nonvascular midrib.
Branching is dichotomous.	Branching is lateral.
Rhizoids are unicellular.	Rhizoids are multicellular and branched.
They have a dorsiventral symmetry. The thallus is closely appressed to the substrate.	Mossee possesses radial symmetry, though it may be erect, hanging or creeping.
Examples: Riccia, Marchantia.	Examples: Funaria, Sphagnum.

Economic Importance

• Prevention of Soil Erosion: Specially mosses form dense mats over the soil and prevent soil erosion.
• Soil Formation: They take part in building soil in rocks and crevices formed by lichens.
• Water Retention: This property is employed to keep seedlings and cut plants moist during transportation and propagation. In older times, Sphagnum was used in place of absorbent cotton.
• Peat: Sphagnum (Bog moss) often grows in acidic marshes. The dead parts of moss and other plants are slowly carbonised, compressed and fossilised over thousands of years to produce a dark spongy mass called peat. The peat blocks are used as fuel. Peat is also good manure. It overcomes soil alkalinity and increases its water retention and aeration.
• Other Uses: They are a good source of animal food in rocky and ice-clad areas.

Pteridophyta

• The root, stem and leaves made up the plant body.
• Pteridophyta has well developed vascular system (xylem and phloem) for the transport of water and other substances, from one part of the plant body to another.
• These are non-flowering plants and do not produce seeds.
• Multicellular sex- organs covered by sterile cells.
• A fertilised egg develops into an embryo.
• Examples: Club mosses – Selaginella, Lycopodium; horsetails – Equisetum; and ferns – Marsilea, Azolla, Adiantum, Dryopteris, Pteris and Pteridium.
• Sperms are flagellate.
• Heteromorphic generation of alternation is present.
• An embryo stage is present.
• The most conspicuous of the pteridophytes are the ferns(Pteropsida).

Ferns

• They are the largest and most advanced group of vascular cryptogams.
• Ferns are plants in humid tropics and temperate areas. Some live under sub-arctic conditions as well.
• The stem is generally an underground rhizome.
• Vegetative reproduction occurs by fragmentation of rhizome, adventitious buds and bulbils, etc.

Gymnospermae

• They are the earliest and most simple seed plants.
• Usually perennial, evergreen and woody plants.
• The seeds produced by these plants are naked and are not enclosed within fruits.
• The two types of sporophylls are usually aggregated to form distinct cones or strobili pollen cones and seed cones.
• Seeds lie exposed on the surface of megasporophylls i.e. naked seeds.
• Gymnosperms include the following two groups: cycads and conifers.

Cycade 

• They are perennial slow-growing small trees found in tropical and sub-tropical regions
• The plant has a life of about 1000 years. 
• Also called the Sago plant.
• They have palm-like habits and fern-like foliage.
• Plants are dioecious.
• The sporophylls aggregate to form spores.
• Example: Cycas, etc.

Conifers

• They are evergreen with massive vascular tissue and non-motile gametes.
• Conifers are monoecious.
• Cones are compact and woody.
• Unlike cycads, they are not produced at the tips of main branches.
• Example: Pinus(pines), Cedrus(deodar), Ginkgo, etc.

Angiospermae

• Angiosperms are highly yielding plants and they produce seeds that are covered within the fruit.
• The reproductive organs (sporophylls) are combined in a flower. They are called flowering plants because these plants have flowers.
• Plant embryos in seeds have structures, called cotyledons. Cotyledons are called ‘seed leaves’ because in numerous cases they emerge and become green when the seed germinates.
• The endosperm has triploid cells.
• Pollination is through several agencies but the most prominent is by animals.
• Archegonia are absent.
• Examples: Maize, Wheat, rice, onion, etc.
• Angiosperms are divided into two sub-groups – dicotyledonous (dicots) and monocotyledonous (monocots) plants mainly on the basis of a number of embryonic leaves or cotyledons.

FAQs on Kingdom Plantae

Question 1: Which division do ferns belong to?

Answer:

Ferns belong to division pteridophyta.

Question 2: What are the major divisions in the Plantae? 

Answer: 

Kingdom plantae includes the following five divisions:

• Thallophyta(Algae)
• Bryophyta
• Pteridophyta
• Gymnospermae
• Angiospermae

Question 3: How are the criteria for deciding divisions in plants different from the criteria for deciding the sub-groups among animals?

Answer:

Because the basic designs of their body is not same. This is due to the fact that plants are autotrophic and non-mobile, while animals are heterotrophic and they can move. The other characteristics such as presence or absence of skeleton, etc., are used to make subgroups among animals.

Question 4: How are pteridophytes different from phanerogams?

Answer: 

The plants belonging to pteridophytes do not produce seeds whereas those belonging to phanerogams produce seeds.

Question 5: How do gymnosperms and angiosperms differ from each other?

Answer:

The gymnosperms have naked seeds(i.e., seeds are not enclosed within the fruits) whereas the angiosperms have seeds inside the fruits.

Question 6: Which plant group is called ‘amphibians’ of the plant world?

Answer:

Bryophyta is known as the amphibians of the plant world.