Classification of Plants: Plants are living organisms found in almost every part of the world. They differ greatly in their size, structure, method of reproduction, uses and length of life. For example, algae are simple plants that can live in water, while trees such as mango and coconut have well-developed roots, stems and leaves.
Because there are many different types of plants, scientists and students need a way to group them according to their similarities and differences. Classification of plants is the systematic grouping of plants based on features such as their body structure, vascular tissues, method of reproduction, seed formation, uses and life cycle.
In agriculture, plants can be classified in three important ways: botanical classification, agricultural classification and classification based on life cycle.
About This Lesson
This lesson explains the major ways plants are classified and gives the characteristics and examples of the main groups. It also compares important plant groups such as bryophytes and spermatophytes, and gymnosperms and angiosperms.
Learning Objectives
At the end of this lesson, students should be able to:
- Explain the meaning of plant classification.
- Describe the major groups in botanical classification.
- State the characteristics and examples of major plant groups.
- Explain the agricultural classification of plants.
- Classify plants according to their life cycle.
- Differentiate between important groups of plants.
Classification of Plants
Plants can be classified using three major methods:
- Botanical classification
- Agricultural classification
- Classification based on life cycle
Botanical Classification of Plants
Botanical classification groups plants according to their structural and reproductive features. In traditional school-level classification, the plant kingdom is divided into groups such as Thallophyta, Bryophyta and Tracheophyta, with Tracheophyta containing Pteridophyta and Spermatophyta.
This traditional classification is useful for understanding the major differences between simple and more complex plants.
Thallophyta
Thallophyta is a traditional group used for simple plant-like organisms, especially algae. Algae may be found in freshwater, marine environments and other moist places.
The major groups of algae commonly studied include:
- Chlorophyta – green algae
- Rhodophyta – red algae
- Phaeophyta – brown algae
Characteristics of Thallophyta
- They have a simple body that is not differentiated into true roots, stems and leaves.
- Some are unicellular, while others are multicellular.
- Many live in aquatic or moist environments.
- Most algae contain chlorophyll and manufacture their own food by photosynthesis.
- They may reproduce sexually or asexually.
- Their bodies may occur as single cells, colonies or filaments.
Examples: Chlamydomonas, Spirogyra and Volvox.
Bryophyta
Bryophytes are small, non-vascular plants commonly found in damp and shady places. They do not have true roots, stems and leaves. Instead, they possess simpler structures that perform similar functions.
Characteristics of Bryophyta
- They are small multicellular plants.
- They lack true vascular tissues.
- They do not have true roots, stems and leaves.
- They are commonly found in moist and shady environments.
- They reproduce by spores.
- They have structures called rhizoids that help them attach to surfaces and absorb water.
- Water is important in their sexual reproduction.
Examples: Mosses and liverworts.
Tracheophyta
Tracheophyta refers to vascular plants. They possess specialised tissues for transporting water, minerals and manufactured food around the plant.
In traditional school classification, Tracheophyta is divided into Pteridophyta and Spermatophyta.
Pteridophyta
Pteridophytes are vascular plants that reproduce by spores rather than seeds. They have true roots, stems and leaves.
Characteristics of Pteridophyta
- They are multicellular plants.
- They possess vascular tissues.
- They have true roots, stems and leaves.
- They do not produce seeds.
- They reproduce mainly by spores.
- Most are terrestrial and commonly grow in moist environments.
Examples: Ferns and horsetails.
Spermatophyta
Spermatophytes are seed-producing plants. They have well-developed vascular tissues and true roots, stems and leaves. In traditional classification, they are divided into gymnosperms and angiosperms.
Gymnosperms
Gymnosperms are seed-producing plants whose seeds are not enclosed inside a fruit. Their seeds are commonly borne on structures such as cones.
Characteristics of Gymnosperms
- They are vascular plants.
- They produce seeds.
- Their seeds are not enclosed in fruits.
- They generally do not produce true flowers.
- Many produce cones.
- They have well-developed roots, stems and leaves.
Examples: Pine, cycad and ginkgo.
Angiosperms
Angiosperms are flowering plants. They produce seeds enclosed within fruits and make up the largest group of living plants.
Characteristics of Angiosperms
- They are vascular plants.
- They produce flowers.
- Their seeds are enclosed within fruits.
- They have well-developed roots, stems and leaves.
- They reproduce through pollination and fertilisation.
- They include many food, fibre, fruit and cash crops.
Examples: Maize, rice, mango, orange, cowpea and groundnut.
Differences Between Gymnosperms and Angiosperms
| Feature | Gymnosperms | Angiosperms |
|---|---|---|
| Flowers | Usually do not produce true flowers | Produce flowers |
| Seeds | Naked or exposed | Enclosed in fruits |
| Cones | Commonly present | Not used to bear seeds |
| Examples | Pine, cycad | Maize, mango, orange |
Monocotyledonous and Dicotyledonous Plants
Angiosperms are traditionally divided into monocotyledonous plants (monocots) and dicotyledonous plants (dicots) based mainly on the number of cotyledons in the seed.
Monocotyledonous Plants
Monocotyledonous plants have one cotyledon in their seeds.
Characteristics of Monocots
- They have one cotyledon.
- Their leaves usually have parallel veins.
- They generally have fibrous root systems.
- Their floral parts are commonly arranged in threes or multiples of three.
- Their vascular bundles are scattered in the stem.
- Most do not show typical secondary thickening.
Examples: Maize, rice, oil palm and grasses.
Dicotyledonous Plants
Dicotyledonous plants traditionally refer to flowering plants with two cotyledons.
Characteristics of Dicots
- They have two cotyledons.
- Their leaves commonly have branching or net-like veins.
- They usually have a tap root system.
- Their floral parts are commonly arranged in fours or fives.
- Their vascular bundles are generally arranged in a ring in the stem.
- Many can undergo secondary growth.
Examples: Mango, orange, cowpea and groundnut.
Agricultural Classification of Plants
Agricultural classification groups plants according to their uses and products. This type of classification is especially important to farmers because it helps identify the purpose of different crops.
| Crop group | Examples |
|---|---|
| Cereal crops | Maize, rice, wheat, millet |
| Grain legumes | Cowpea, soybean, groundnut, pigeon pea |
| Root and tuber crops | Cassava, yam, sweet potato, cocoyam |
| Vegetable crops | Tomato, okra, spinach, amaranthus |
| Fruit crops | Mango, orange, banana, pineapple |
| Beverage crops | Cocoa, coffee, tea |
| Spice crops | Ginger, pepper |
| Oil crops | Oil palm, soybean, groundnut, coconut |
| Fibre crops | Cotton, sisal, kenaf |
| Latex crops | Rubber |
Some crops may belong to more than one useful category depending on the part being considered and how the crop is used. For example, groundnut is both a grain legume and an important oil crop.
Classification of Plants Based on Life Cycle
Plants can also be classified according to the length of time they take to complete their life cycle.
The three major groups are annuals, biennials and perennials.
Annual Plants
Annual plants complete their life cycle within one growing season or year. They germinate, grow, produce flowers and seeds, and then die.
Examples: Maize, rice, cowpea, millet and groundnut.
Biennial Plants
Biennial plants normally complete their life cycle over two growing seasons. During the first year, they mainly develop vegetative structures. They flower and produce seeds during the second year before completing their life cycle.
Examples: Carrot, onion and some varieties of cabbage.
Perennial Plants
Perennial plants live and produce for more than two years. Some can remain productive for many years under suitable environmental conditions.
Examples: Mango, orange, cocoa, rubber and oil palm.
Summary
The classification of plants makes it easier to study the enormous variety of plants and understand their similarities and differences. In school biology and agriculture, plants are commonly classified botanically, according to their agricultural uses, and according to their life cycle.
Botanical classification considers features such as vascular tissues, seeds and reproductive structures. Agricultural classification groups crops according to their uses, while life-cycle classification groups plants as annuals, biennials or perennials.
Revision Questions
- What is plant classification?
- State the three major methods of classifying plants.
- Mention four characteristics of Bryophyta.
- What are vascular plants?
- State three characteristics of Pteridophyta.
- Differentiate between gymnosperms and angiosperms.
- State four characteristics of monocotyledonous plants.
- Give four examples of dicotyledonous plants.
- Explain agricultural classification of plants and give five examples of crop groups.
- Differentiate between annual, biennial and perennial plants.