Plant Kingdom

Introduction

The living organisms found on the earth are different in their structures, habit, habitat, mode of nutrition and physiology. The estimated number of species on the earth is 8.7 million. Among them 6.5 million (1 million =10 lacks) species are living on land, 2.2 million species in the ocean.

In these 4, 00,000 species are flowering plants. The living organisms show lot of similarities and differences so that they can be arranged into many groups systematically.

The plant kingdom includes thallophytes, bryophytes, pteridophytes, gymnosperms and angiosperms.

1. Taxonomy

Taxonomy is the branch of biology that deals with the study of identification, classification, description and nomenclature of living organisms. The word taxonomy is derived from two Greek words (Taxis: arrangement and Nomos: laws.) The word ‘Taxonomy’ was first coined by Augustin-Pyramus de Candolle.

Classification:

Plants are arranged into different groups and categories on the basis of similarities and differences are called classification.

Types of classification:

There are four types of classification.

1. Artificial system of classification

2. Natural system of classification

3. Phylogenetic system of classification

4. Modern system of classification

1.1 Artificial system of classification

This is the earliest system of classification in plants. Plants are classified on the basis of one or few morphological characters. The most famous artificial system of classification is Linnaeus classification which was proposed by Carolus Linnaeus in Species plantarum.

1.2 Natural system of classification

In this system, plants are classified on the basis of several characters. Bentham and Hooker’s classification is an example of Natural System of Classification. This system of classification is based on morphological and reproductive characters of the seeded plants. This classification is widely used in many Herbaria and botanical gardens all over the world.

2. Outline Of Bentham And Hooker’s System of Classification

The division spermatophyta are divided into 3 classes:

Class I - Dicotyledonae

· Seed has two cotyledons.

· Leaves have reticulate venation

· Tap root system is present.

· Flowers are tetramerous or pentamerous.

Class II - Gymnospermae (Naked seed plants)

· Plants of this class have no fruit.

· It has three families, they are

1. Cycadaceae

2. Coniferae

3. Gnetaceae

Class III - Monocotyledonae

· Seed has single cotyledon.

· Leaves have parallel venation.

· Fibrous root system is present

· Flowers are Trimerous

3. Binomial Nomenclature

The naming of an organisms with two words are known as Binomial Nomenclature. For example, the binomial name of mango is Mangifera indica. Here the first word Mangifera refers to the genus name and the second word indica to the species name.

The system of naming the plants on scientific basis is known as Botanical nomenclature. Binomial name was first introduced by Gaspard Bauhin in the year of 1623.

4. Salient features of Algae

· Algae are chlorophyll bearing simple, primitive plants and are autotrophs.

· Algae belongs to thallophyta, and the plant body of algae are called thallus. i.e. the plant body is not differentiated into root, stem and leaf.

· Most of the algae are living in aquatic region. It may be fresh water or marine water. Very few algae can survive in terrestrial conditions.

· Some algae are very minute and float on the surface of the water. These algae are called Phytoplankton.

· Some of the algae are symbionts (algae living with fungi and they both are mutually benefitted.)

o E.g. Lichen.

· A few species of them are epiphytes (growing on another plants).

Various forms of Algae:

· Plant body of the algae are unicellular or multicellular

· Unicellular motile (Chlamydomonas), nonmotile. (Chlorella)

· Multicellular unbranched filaments (Spirogyra) and branched filaments (Cladophora).

· Some algae are giant kelp – Macrocystis.

· Some algae are living as colonial form – Volvox.

· Alga like Chara resembles largest plant body and it possess well developed sex organs.

Reproduction of Algae:

· Three types of reproduction are seen in algae.

· Vegetative reproduction by fragmentation e.g. Spirogyra.

· Asexual reproduction by spore formation e.g. Chlamydomonos.

· Sexual reproduction by means of fusion of gametes e.g. Spirogyra, Chara

4.1  Classification of algae based on pigments (Fritsch – 1935)

4.2 Economic Importance of algae:

i. Food:

· Algae are consumed as food by the people in Japan, England and also in India. e.g. Ulva, Spirulina, Chlorella etc..

· Some algae are used as a food for domestic animals. e.g. Laminaria, Ascophyllum.

ii. Agriculture

· Some of the blue green algae are essential for the fixing of atmospheric nitrogen into the soil, which increases the fertility of the soil.

E.g. Nostoc, Anabaena.

iii. Agar Agar Agar

· Agar is extracted from some red algae, namely Gelidium, Gracillaria, etc., which is used to prepare growth medium in laboratories.

iv. Iodine

· Iodine is obtained from brown algae like Laminaria (kelp).

v. Algae in space Travel

· Chlorella pyrenoidosa is used in spacew travel to get rid of CO2 and decompose human wastes.

vi. SCP (Single Cell protein)

· Some of the single cell algae and blue green algae are used to produce protein.

E.g. Chlorella, Spirulina.

5. Fungi

5.1 General characters of fungi

Fungi (singular – fungus) belongs to thallophyta because the plant body is not differentiated into root, stem, and leaves.

· The plant body of fungus consists of filament like structures called as hyphae. Several hyphae arranged in the form of network called mycelium.

· There are two types of mycelium found in fungi, namely septate mycelium and aseptate mycelium.

· If the cross wall is seen between the cell, it is called septate mycelium. If the cross wall is not seen, it is called aseptate mycelium.

· When aseptate mycelium contains many nuclei it is called as coenocytic mycelium.

· The cells of fungi are multicellular and eukaryotic organisation.

· Some species of fungi like yeast is unicellular and eukaryotic cell. Cell wall of fungi is made up of a chemical substance called chitin.

· Heterotrophs are of three types called parasites, saprophytes and symbionts.

The reserve food materials of fungi are glycogen and oil. They have no starch because they have no chlorophyll pigments. So, they are heterotrophs.

Parasites

Ø Parasites absorbs food from the living organisms with the help of special root called haustoria. E.g. Cercospora personata.

Ø It affects groundnut plants and cause Tikka disease.

Saprophytes:

Saprophytes grow up on the dead and decay matters and get food from them. E.g. Rhizopus.

Symbionts:

Ø Some species of fungi living with algae and are mutually benefitted. E.g. Lichen.

Ø Some fungi live symbiotically with higher plants roots called Mycorrhizae.

5.2 Classification of fungi (Martin 1961)

5.3 Economic Importance of Fungi:

i. Antibiotic:

Penicillin (Penicillium notatum), Neomycin, Gentamycin, Erythromycin are some antibiotics obtained from fungi, which cure variable diseases.

ii. Food:

Mushroom contains rich protein and minerals. The most common edible mushroom is Agaricus. (Button mushroom).

iii. Vitamins:

Fungus like Ashbya gospii and E r y m o t h e c i u m ashbyii are used to produce vitamin B2 (riboflavin).

iv. Alcohol:

Fungus like yeast contain enzymes invertase and zymase, which ferment the sugar molasses into alcohol.

5.4 Harmful Effects of Fungi

Plant Diseases:

These are incited by different agents — bacteria, viruses, cell-worms and fungi; of these the fungi cause the most severe losses. They destroy field crops, forage crops, fruit and nut crops, vegetable crops, drug plant crops and ornamental crops.

Disease causing fungi are found in class Phycomycetes, Ascomycetes, Basidiomycetes and Fungi Imperfecti. No species of Myxomycetes are known to cause disease in plants, except mushrooms.

Human Diseases:

Several fungi are responsible formycoses and tropical diseases of man and animals. Some of the important diseases caused by fungi are given in the related table.

6. Bryophytes

6.1 General Characters of Bryophytes

· Bryophytes are the primitive and simplest group of land plants.

· These are terrestrial and non-vascular cryptogams (they have no vascular tissues like xylem, phloem).

· Water is essential to complete their life cycle, so these plants are called amphibians of the Plant Kingdom.

· The gametophytic plant can be either thalloid (liverworts) or leafy (mosses).

· The plant remains fixed to the substratum with the help of root like structure called rhizoid.

· Sexual reproduction is oogamous type

· They have well developed sex organs like antheridia and archegonia.

· The male sex organ is antheridium, which produces antherozoid. The female sex organ is archegonium which contains an egg.

· Antherozoid swims and reaches the archegonium, fertilizes the egg and form zygote (2n).

· Zygote is the first cell which develops into sporophytic generation and produce haploid spore (n) by meiosis.

· Spore is the first cell of the gametophytic generation.

Bryophytes have distinct alternation of generation. Gametophytic is dominant and sporophytic generation is small and depends on the gametophytic generation.

6.2 Classification of Bryophytes

Class I Hepaticae (e.g. Riccia)

· These are lower forms of bryophytes. They are simple in structure than moss.

· Protonemal stage is absent. Sporophyte is very simple and short lived.

Class–II Anthocerotae (e.g. Anthoceros)

· Gametophyte is undifferentiated thallus, rhizoids are unicellular and unbranched.

· Protonemal stage is absent. Sporophyte is differentiated into foot and capsule only.

Class-III Musci (e.g. Funaria)

· These are higher forms in which the gametophytes is differentiated into stem like, leaf like parts.

· Protonemal stage is present.

· Sporophytes is differentiated into foot, seta, and capsule.

6.3 Economic Importance of Bryophytes:

· Bryophytes prevent the soil erosion.

· Sphagnam can absorb large amount of water. Hence, it is used by the gardeners in nursery.

· Peat is a valuable fuel like coal obtained from Sphagnum.

7. Pteridophytes

7.1 General Characters of Pteridophyte:

· Pteridophytes are the first true land plants with xylem and phloem. Hence it is called vascular cryptogams.

· Pteridophytes also exhibit alternation of generation. The diploid sporophytic phase alternates with the haploid gametophytic phase.

· The main plant body is sporophytes, which is the dominant phase, differentiated into true root, stem and leaves.

· Sporophytes reproduce by means of spores. Spores are produced in sporangium.

· The sporangia bearing leaves are called sporophyll.

· Most of the plants produce only one type of spore, it may be either microspore or megaspore (homosporous).

· In some plants two types of spores are produced. They are microspore and megaspore (heterosporous).

· Spores give rise to gametophytic generation called prothallus, which is short lived and independent.

· The gametophytes produce the multicellular sex organs, Antheridium which produces antherozoid (male gamete) and archegonium which contains an egg. (female gamete)

· The antherozoid fertilizes with egg and form diploid zygote. It develops into an embryo which grow differentiate into sporophyte.

7.2 Classification of Pteridophytes:

7.3 Economic Importance of Pteridophytes:

· Ferns are used as ornamental plants.

· The rhizome and petioles of the Dryopteris yield the vermifuge drug.

· The sporocarp of Marsilea (water fern) is used as food by tribal people.

8. Differences between Bryophytes and Pteridophytes

S.NO	Bryophytes	Pteridophytes
1	Plant body cannot be differentiated into root, stem and leaf.	Plant body can be differentiated into root, stem and leaf.
2	Bryophytes are amphibians.	Pteridophytes are land plants.
3	Vascular tissues are absent.	Vascular tissues are present.
4	The dominant phase of the plant body is gametophyte.	The dominant phase of the plant body is sporophyte.
5	Sporophytic generation depends on the gametophytic generation. e.g. Riccia	Gametophytic generation does not depend on sporophytic generation. Eg. Selaginella

9. Gymnosperms

9.1 General Characters of Gymnosperms

· Gymnosperm are naked seed plant, i.e. the ovule is not enclosed by ovary.

· Gymnosperms have two phases in its life cycle. (Sporophytic and Gametophytic)

· Plant body is sporophyte dominant which is differentiated into root, stem and leaf.

· They have well developed vascular tissues. (xylem and phloem)

· The water conducting tissue is tracheid. Food conducting tissue is sieve cell.

· They have cone on which sporangia and spores are produced.

9.2 Economic Importance of Gymnosperms

· Woods of many conifers are used in the paper industries. e.g. Pinus, Agathis

· Conifers are the sources of soft wood for construction, packing and plywood industry e.g. Cedrus, Agathis

· Turpentine is an essential oil used for paint preparation extracted from the resin of Pinus. It is also used medicinally to get relief from pain and bronchitis etc.,

· Seeds of Pinus gerardiana are edible.

· Ephedrine is an alkaloid extracted from Ephedra. It cures asthma and respiratory problems.

· Araucaria bidwillii is an ornamental plant.

9.3 Classification of Gymnosperms

10. Angiosperms (Closed seeded plants)

10.1 General Characters of Angiosperms

· Angiosperms are called flowering plants. In this group more than 4, 00,000 living species are found.

· They occupy every habitat on earth except extreme environment. (Extreme hot and cold conditions).

· Habit of the plants may be herb, (Solanaum melongena) shrub, (Hibiscus rosasinensis) and tree – Mangifera indica (Mango)

· They have well developed conducting tissues. (Vascular bundles)

· Xylem contains vessel, tracheid, and xylem parenchyma and xylem fibre.

· Phloem contains sieve tubes, phloem parenchyma, companion cells and phloem fibres.

10.2 Classification of Angiosperms

Angiosperms are divided into two classes, they are:

· Monocotyledons

· Dicotyledons

10.3 Characteristic features of monocotyledons

· Seed has only one cotyledon.

· Plants have fibrous root system, leaves with parallel venation.

· Flowers are trimerous and not differentiated in to calyx and corolla.

· Pollination occurs mostly by wind.

· E.g. Grass, Paddy, Banana.

10.4 Characteristic features of Dicotyledons

· Seed has two cotyledons.

· Plants have tap root system, leaves with reticulate venation.

· Flowers are tetramerous or pentamerous. Calyx and corolla are well differentiated.

· Pollination occurs mostly by insects.

· E.g. Bean, Mango, Neem

11. Uses of Medicinal plants

11.1 Acalypha indica

· It belongs to the family Euphorbiaceae.

· The paste obtained from the leaves of this plant is used to cure the burns on the skin.

· The juice of this plant leaves is mixed with lemon juice to cure ringworm.

11.2 Aegle marmelos

· It belongs to the family Rutaceae.

· The unripe fruit of this tree is used to treat indigestion.

· It is used to cure chronic, diarrhoea and dysentery.

11.3 Solanum trilobatum

· It belongs to the family Solanaceae.

· The leaves and fruits of this plant cure cough and cold.

· It is widely used in the treatment of tuberculosis and bronchial asthma.

11.4 Phyllanthus amarus

· It belongs to the family Euphorbiaceae.

· The entire plant is used for the treatment of jaundice.

· It gives additional strength to human liver and used to treat other liver disorders.

11.5 Aloe vera

· It belongs to the family Liliaceous.

· Leaves of this plant is used to cure piles and inflammations on the skin.

· It cures peptic ulcer.