CLASSIFICATION OF PLANTS

Plants are generally classified based on three major criteria. These are:

1. Botanical classification.
2. Agricultural classification.
3. Classification based on life cycle.

 

BOTANICAL CLASSIFICATION OF PLANTS

Plants are generally classified through the botanical method and the use of binomial system. The botanical classification has been discussed below, where the plant kingdom is divided into: Schizophyta, Thallophyta, Bryophyta, Pteridophyta and Spermatophyta. Read the characteristics and examples of these groups below under the sub-topic: “Kingdom plantae.”

 

Kingdom: Plantae

The plant kingdom consists of three main divisions (Phyla). These are:

1. Thallophyta (e.g. Green brown, red algae).
2. Bryophyta (Liverworts and mosses).
3. Tracheophyta (Vascular plants).

 

Thallophyta

This group can further be subdivided into three groupings. These are:

• Rhodophyta (Red algae).
• Chlorophyta (Green algae).
• Phaecophyta (Brown algae).

 

Characteristics

• These are simple microscopic plants.
• Some are unicellular, e.g. chlamydomonas, while others are multicellular, e.g. Spirogyra.
• They are simple aquatic plants.
• They have no true roots, stems and leaves.
• They have cellular cell walls.
• Algae are mainly autotrophic plants, i.e ., they can synthesize their own food.
• Algae are filamentous and the cells are not differentiated into tissues.
• They have no specialised reproductive organs or cells but can exhibit sexual and asexual means of reproduction.
• Examples are the single free living algae like chlamydomonas or in form of filaments, e.g. spirogyra or in colonies e.g. volvox.

 

Bryophyta

Characteristics

• They are complex, multicellular green plants.
• Their cells are differentiated into tissues.
• They lack true roots, stems and leaves but have structures resembling roots, stems and leaves.
• They are non-vascular plants.
• They are usually found growing in moist places.
• Some bryophytes are terrestrial while others are aquatic.
• They exhibit asexual reproduction by spores in which there is alteration of generation and sexually by gametes.
• Examples are mosses and liverworts.

 

Tracheophyta

This division is made up of vascular plants. This division is grouped into two subdivisions to include:

1. Pteridophyta.
2. Spermatophyta.

 

Pteridophyta

Characteristics

• They are multicellular and vascular green plants.
• They are non-flowering plants.
• They have true roots, stems and leaves.
• They are mainly terrestrial plants while few are aquatic.
• They are non-seed producing plants.
• They reproduce sexually by spores.
• Example is the ferns and it includes dryopteris, felimas and water ferns.

 

Spermatophyta

Characteristics

• They are multicellular, seed producing flowering plants.
• They are vascular plants and have well developed vascular tissues.
• They have true roots, stems and leaves.
• They reproduce sexually and do not need water for reproduction.
• They are mainly terrestrial green plants.

 

Differences Between Spermatophytes and Bryophytes

 

Spermatophytes

• They have well developed vascular bundles.
• Stems are present.
• They have true leaves.
• They reproduce by flowers (seeds)
• They have well developed roots.

 

Bryophytes

• Vascular bundles are absent.
• Stems are absent.
• They have leaf-like structures or no true leaves.
• They reproduce by spores.
• They have rhizoids, i.e ., no true roots.

 

Spermatophyta can be, divided into two main classes: These are Gymnosperms and Angiosperms.

 

(a) Gymnosperms

Characteristics

• These are plants with naked seeds.
• They do not bear flowers.
• They have true roots, stems and leaves.
• The seeds are borne on special structures called cones.
• They are vascular green plants.
• Examples are pine and cycads, gingkos and conifers.

 

(b) Angiosperms

Characteristics

• They are the most complex green flowering plants.
• They are vascular plants.
• They have well developed and complete flowers.
• They are seed plants with seeds enclosed in the fruit.
• They are mainly terrestrial plants.
• They show more specialised reproductive mechanism involving pollination and fertilization.

 

Differences Between Gymnosperm and Angiosperm

 

Gymnosperm

• They do not bear flowers.
• Seeds are naked.
• Seeds are borne on cones.

 

Angiosperm

• They bear flowers.
• Seeds are enclosed.
• Seeds develop from ovules and are enclosed in the ovary.

 

Divisions of Angiosperm

Angiosperms can be sub-divided into two classes according to the number of seed leaves (cotyledons). These are:

1. Dicotyledonous plants.
2. Monocotyledonous plants.

 

Dicotyledonous Plants

Characteristics

• They bear seeds which have two seed leaves or cotyledons.
• The vascular bundles of each stem are arranged in a regular pattern.
• Their floral parts exist in groups of four or five.
• The leaves have veins arranged in branched network.
• They have tap root system.
• They usually undergo secondary growth.
• Examples are mango, orange, cowpea, groundnut, balsam plant.

 

Monocotyledonous Plants

Characteristics

• They bear seeds which have only one seed leaf (cotyledon).
• The vascular bundles of the stem are scattered.
• Their floral parts exist in groups of three or multiples of three.
• Their leaves have veins running parallel to one another.
• They have fibrous root system.
• They do not undergo secondary growth.
• Examples are maize plant, rice, oil palm trees and guinea grass.

 

Differences Between Monocotyledonous and Dicotyledonous plants

Monocotyledonous plants

• They possess only one seed leaf or cotyledon.
• They have scattered vascular bundles of stem.
• They have fibrous root system.
• They exhibit hypogeal germination.
• Floral parts exist in groups of three or multiples of three.
• They possess parallel venation.
• There is presence of large pith, ring of vascular bundle in the centre of ste.
• They do not undergo secondary growth.

 

Dicotyledonous plants

• They possess two seed leaves or cotyledons.
• Vascular bundles of stem are arranged in regular pattern.
• They have tap root system,
• They exhibit epigeal germination.
• The floral parts exist in groups of four or five.
• They possess net venation.
• There is presence of xylem (water conducting)
• They undergo secondary growth.

 

AGRICULTURAL CLASSIFICATION OF PLANTS

Agricultural classification of plants is the type of classification based on the uses of plants. In this classification, crops or plants are grouped into the following categories based on their uses. some of these crops are:

1. Cereal plants: These plants belong to the grass family and they provide carbohydrate, e.g. maize, rice, millet, guinea corn, wheat, barley and oats.
2. Pulses (grain legumes): Pulses are crops which provide proteins for man and animals when eaten.e.g. cowpea, soyabeans, groundut, lima beans and pigeon pea.
3. Roots and tuber crops: These crops produce tubers under the ground and they provide carbohydrate to human and animals when eaten, e.g. cassava, yam, cocoyam, sweet potato, Irish potato, beets and carrot.
4. Vegetable crops: Vegetable crops provide vitamins and minerals to human and animals when consumed, e.g. tomatoes, amaranthus, onion, okra, cauliflower, spinach, bitter leaf and water leaves.
5. Fruit plants: Fruit plants also provide vitamins and minerals to human and animals when consumed, e.g. orange, banana, pineapple, mango, pawpaw and cashew.
6. Beverage plants: These crop plants provide food drinks when processed into finished products like bournvita, ovaltine, pronto, etc. Examples of beverage crops are cocoa, coffee, tea and kola.
7. Spices: These crop plants provide vitamins and minerals to man and animals when consumed, e.g. ginger, pepper, and onion.
8. Oil plants: Oil plants can provide oil when processed both for domestic and industrial uses, e.g. oil palm, groundnut, melon, coconut, soyabean and cotton.
9. Fibre crops: These are crop plants used for making clothing materials, ropes and bags, e.g. cotton, sisal, hemp, kenaf, and hibiscus.
10. Latex crops: These are crops which provide some white, sticky liquid (latex) used in plastic industries, e.g. rubber.

 

CLASSIFICATION OF PLANTS BASED ON LIFE CYCLE

In the classification based on life cycle, plants are grouped into three categories based on their life cycle or the life span of the crop plants, or the number of years a plant is able to grow, mature and produce fruit. the groups are:

1. Annuals: Annuals are plants which complete their life cycles in one season. in other words, the plants grow, mature, produce fruits and die within one year. Examples of annual plants are maize, rice, cowpea, millet, vegetable, cotton and groundnut.
2. Biennials: These are plans which complete their life cycles within two years. These plants develop their vegetative parts during the first year and produce fruits and die during the second years. Examples of biennial plants are pepper, carrot, onion and ginger.
3. Perennials: Perennial plants grow, mature and produce fruits for more than two years. In this case, some plants can life for three, five, ten or even over 20 years. Examples of perennial plants are cocoa, banana, orange, oil palm, rubber and mango.