Plant Kingdom – Types, Classification, Characteristics and Differences between Plants and Animals

The Biology Topics of biotechnology involve using living organisms to develop new products or solve problems.

Kingdom Plantae: Definition, Classification and Examples

Kingdom Plantae is further divided into various divisions based on various criteria. The first level of classification among plants depends on whether or not the plant body has well-differentiated, distinct 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. Further classification of plants involves criteria, such as the ability to bear seeds and whether the seeds are enclosed within fruits.

Classification of Algae

(L. alga = seaweed)

• Most primitive and simple plants. The plant body is not differentiated into stem, root, and leaves, but it is in the form of an undivided thallus.
• Most algae are water-growing or aquatic, (both marine and freshwater); some are terrestrial, i.e., live on land near moist places.
• Usually contain green pigment for photosynthesis; some algae have other photosynthetic pigments such as red, brown, and purple. These pigments form the basis of further classification of algae.
• They are autotrophic, i.e., manufacture their own food. Reserve food is generally starch.
• They have a cellulose cell wall around their cells.
• Mechanical and conducting tissues are absent (i.e., there is no vascular system).
• Asexual reproduction generally takes place by spores.
• Sex organs are simple, single-celled and there is no embryo formation after fertilization.
• In their life-cycle, the gamete-producing haploid phase called the gametophytic phase is dominant.
• The short spore-bearing diploid phase, the sporophytic phase, does not remain attached to the gametophyte.

Examples: Green algae – Ulothrix, Cladophora, Spirogyra, Ulva, and Chara; red algae – Batra, Polysiphonia; brown algae (Laminaria, Fucus, Sargassum).

Major Divisions of Bryophytes

(Gr., Bryon – a moss, a liverwort)

• Bryophytes are small multicellular green land plants. These simple land plants are confined to shady damp places. They are also called 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 them.
• Gametophyte is attached to a substratum by means of hair-like outgrowths, the rhizoids, which absorb water and minerals from the substratum. Sporophytes live as a parasite over gametophytes.
• The sex organs are multicellular.
• An embryo is formed upon fertilization.

Examples: Riccia, Marchantia, Anthoceros, Funaria, Barbula

Differences between Bryophyta and Pteriodophyta

Bryophyta	Pteridophyta
1. Plant body is gametophytic.	1. Plant body is sporophytic.
2. Plant body is either thallose and/or foliose. However, real stems and leaves are always absent.	2. Real stems and leaves are present.
3. Fixation of the plant body is carried out by rhizoids.	3. Fixation of the plant body is carried out by roots.
4. Sporophyte is parasitic over the gametophytic plant body throughout its life.	4. The gametophyte is small and independent.
5. Bryophytes are non-vascular in nature.	5. Pteridophytes are vascular plants.

Differences between Pteridophytes and Phanerogams (Spermatophytes)

Pteridophytes	Phanaerogams/Spermatophytes
1. They are seedless plants.	1. They are seed-bearing plants.
2. Gametophytes are small but independent.	2. Gametophytes are nutritionally dependent on the sporophyte.
3. Their reproductive organs are inconspicuous.	3. Their reproductive organs are quite conspicuous.
4. An external water source is required for fertilization.	4. Fertilization does not require an external water source.

Classification of Pteridophyta

(Gr., Pteris, – idos fern)

• They are found mainly in shady or damp places.
• The plant body is made up of root, stem, and leaves.
• They have well developed vascular system (xylem and phloem) for the conduction of water and other substances, from one part of the plant body to another.
• These plants have no flowers and do not produce seeds.
• Sex organs are multicellular and jacketed by sterile cells.
• Fertilised egg develops into an embryo.

Examples: Club mosses-Selaginella, Lycopodium (“ground pine”); horsetails-Eguzsefwm; and fems-Marsilea, Azolla, Adiantum, Dryopteris, Pteris and Pteridium.

Cryptogamae and Phanerogamae
Two subkingdoms of the kingdom Plantae according to the old classification system
The plant kingdom, according to Eichler (1883), includes all those organisms which possess clearly defined cell walls. This kingdom is subdivided into two sub-kingdoms.

Subkingdom Cryptogamae
(Gr., Crypto-hidden; gamous-marriage).
This subkingdom includes those plants which do not produce external flowers or seeds. Thus, they are considered to bear hidden reproductive organs. The common means of reproduction of cryptogam is by spores. The cryptogams are, therefore, also known as flowerless plants, seedless plants or lower plants. The subkingdom cryptogamae is further divided into three divisions: Thallophyta, Bryophyta, and Pteridophyta.

Division Thallophyta
(Gr. thallus-plant-body without root, stem, and leaves; phyton a plant)

• This division includes most simple, prokaryotic, or simple eukaryotic plants.
• The plant body is in the form of undivided thallus i.e., the plant body is not differentiated into stem, root, and true leaves.
• The vascular tissues (xylem and phloem) are absent i.e., there is no vascular system.
• The reproductive organs are simple one-celled (unicellular).
• There is no embryo formation after fertilization.

The division Thallophyta is divided into three distinct subdivisions: algae (including cyanobacteria or blue-green algae), fungi (including bacteria, slime moulds, and true fungi), and lichens.

Subkingdom Phanerogamae

• Phanerogamae includes higher plants that bear flowers and seeds. Seeds are the result of the reproductive process. They contain an embryo along with stored food, which serves for the initial growth of the embryo during germination.
• The plant body is sporophytic and differentiated into root, stem, and leaves.
• The vascular system (xylem and phloem) is well developed.
• Sex organs are multicellular.
• An embryo develops from a fertilized egg.

On the basis of the absence or presence of fruits, the group of seed-bearing plants is further divided into two subgroups: Gymnospermae and Angiospermae.

On the basis of naked or protected (covered) ovules and the absence or presence of fruits, the subkingdom Phanerogamae is further divided into subdivisions: Gymnospermae and Angiospermae (Both sub-divisions belong to division spermophytic).

Differences between Cryptogamae and Phanaerogamae

Cryptogamae	Phanaerogamae
1. It contains seedless plants.	1. It contains plants with seeds.
2. It includes both vascular and non-vascular plants.	2. It includes only vascular plants.
3. An external water (source) is required for fertilization.	3. An external water (source) is not required for fertilization.

Differences between Algae and Fungi

Algae	Fungi
1. They contain photosynthetic pigments.	1. Photosynthetic pigments are absent in them.
2. Algae are autotrophic.	2. Fungi are heterotrophic.
3. Most of the algae are aquatic in their habitat.	3. Most of the fungi are terrestrial in their habitat.
4. The cell wall is made of cellulose.	4. The cell wall is made of chitin.
5. Algae contain starch as a stored food material.	5. Fungi contain glycogen and oil as the stored food materials.

Characteristics and Classification of Gymnosperms

(Gr., gymno- naked; Sperma- seed)

• They are the most primitive and simple seed plants.
• The seeds produced by these plants are naked and are not enclosed within fruits.
• Usually perennial, evergreen, and woody plants.
• Sporophylls are aggregated to form cones. There are separate male and female cones.
• Xylem lacks vessels and the phloem lacks companion cells.

Gymnospermae includes the following two groups:

• Cycadae. e.g., Cycas, etc.
• Coniferae. e.g., Pinus (pines), Cedrus (deodar), Ginkgo, etc.

Differences between Gymnosperms and Angiosperms

Gymnosperms	Angiosperms
1. Sporophylls are aggregated to form cones.	1. Sporophylls are aggregated to form flowers.
2. The seeds are naked.	2. The seeds are enclosed by a fruit wall.
3. The microspores and megaspores are produced by male and female cones.	3. Microspores and megaspores are produced in the same or two different types of flowers.
4. Vascular tissues such as the xylem lacks vessels and the phloem lacks companion cells.	4. Vascular tissues such as the xylem contain vessels and the phloem contains companion cells.
5. The ovules are not contained within an ovary.	5. The ovules are enclosed within an ovary.
6. Endosperm cells are haploid.	6. Endosperm cells are triploid.

Characteristics of Angiosperms

(Gr., angeion-case; sperma-seed)

• Angiosperms are highly evolved plants and they produce seeds that are enclosed within the fruit.
• The reproductive organs (sporophylls) are aggregated in a flower. Since these plants have flowers, they are called flowering plants.
• Plant embryos in seeds have structures, called cotyledons. Cotyledons are called ‘seed leaves’ because in many cases they emerge and become green when the seed germinates. Thus, cotyledons represent a bit of a pre-designed plant in the seed.
• Endosperm has triploid cells. It supplies nutrients for the developing embryo in the seed.

On the basis of the number of cotyledons (fleshy embryonic leaves), the angiosperms are divided into two groups: dicotyledons and monocotyledons.

Dicotyledonae (Dicots)

• The seeds produced by these plants have embryos with two fleshy leaves, the cotyledons.
• Their leaves have reticulate venation, with a network of veins.
• The root system has a prominent tap root.
• The flowers have five or multiple five petals.
• The vascular bundles are arranged in a ring. They are open (i.e., have cambium) and undergo secondary growth.

Examples: Pea (Pisum sativum), potato (Solanum tuberosum), sunflower (Helianthus annuus), rose (Rosa Indica), banyan (Ficus religiosa), margosa or neem (Azadirachta indica), apple (Malus silvestris), mustard, mango, etc.

Monocotyledonae (Monocots)

• The seeds of these plants have only one cotyledon.
• Their leaves have parallel venation.
• The root system consists of similar fibrous roots.
• The flowers are trimerous, i.e., have three or multiple three petals.
• The vascular bundles are scattered and closed (i.e., lack cambium). Secondary growth does not occur.

Examples: Maize (Zea mays), wheat (Triticum vulgare), rice (Oryza sativa), onion (Allium cepa), sugarcane (Saccharum officinarum), barley (Hordeum vulgare), banana (Musa paradisiaca), Coconut (Cocos nucifera), bamboo and grasses.

Differences between Dicotyledonae and Monocotyledonae

Dicotyledonae	Monocotyledonae
1. In the seed, the embryo bears two cotyledons.	1. In the seeds, the embryo bears one cotyledon.
2. Leaves of these plants have reticulate venation.	2. Leaves of these plants have parallel venation.
3. Vascular bundles of the stem are open and arranged in a ring.	3. Vascular bundles of the stem are closed and scattered in the ground tissue.
4. Secondary growth occurs.	4. Secondary growth does not occur.
5. The plants have a tap root system.	5. The plants have an adventitious root system.
6. Flowers are pentamerous (have five of each floral part) or tetramerous.	6. Flowers are trimerous (have three of each floral part).

Differences between Plants and Animals

Plants	Animals
1. They have less definite shapes and sizes.	1. They have definite shapes and sizes.
2. They are usually branched.	2. They are unbranched except for the sponges.
3. Plant organs are generally external, e.g., root, stem, leaf, flower, etc.	3. Animal organs are generally internal, e.g., liver, heart, kidney, lungs, brain, stomach, etc.
4. The growth of the plant body is often unlimited and continues till death. The growth regions are localized at the tips.	4. The growth of an animal’s body is limited and it stops long before death. The growth regions are not localized.
5. Plants are fixed and cannot perform locomotion. (Exceptions include Chlamydomonas, Volvox, etc.)	5. They can move bodily from one place to another. (Exceptions are sponges and corals (which remain fixed but can move their body parts e.g., tentacles in corals).
6. They have an autotrophic mode of nutrition (i.e., photosynthesis), because they have green pigment, the chlorophyll.	6. They lack chlorophyll and are heterotrophic in their mode of nutrition.
7. Reserve food of plants is starch and oil.	7. Reserve food of animals is glycogen and fat.
8. Plants do not contain sense organs and a nervous system.	8. Animals have sense organs and a nervous system.
9. Response to external stimuli is slow.	9. Response to external stimuli is quick.
10. Each plant cell typically has a cell wall, plastids, and large-sized vacuoles. It lacks the centrosome.	10. Each animal cell typically has no cell wall and plastids. It contains a centrosome.
11. Plants do not contain excretory organs.	11. Animals have distinct excretory organs.
12. asexual reproduction or vegetative reproduction is common in plants.	12. The asexual reproduction occurs only in the lower animals.